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Sample records for oxygen vacancies vo

  1. Oxygen vacancies: The origin of n -type conductivity in ZnO

    Science.gov (United States)

    Liu, Lishu; Mei, Zengxia; Tang, Aihua; Azarov, Alexander; Kuznetsov, Andrej; Xue, Qi-Kun; Du, Xiaolong

    2016-06-01

    Oxygen vacancy (VO) is a common native point defect that plays crucial roles in determining the physical and chemical properties of metal oxides such as ZnO. However, fundamental understanding of VO is still very sparse. Specifically, whether VO is mainly responsible for the n -type conductivity in ZnO has been still unsettled in the past 50 years. Here, we report on a study of oxygen self-diffusion by conceiving and growing oxygen-isotope ZnO heterostructures with delicately controlled chemical potential and Fermi level. The diffusion process is found to be predominantly mediated by VO. We further demonstrate that, in contrast to the general belief of their neutral attribute, the oxygen vacancies in ZnO are actually +2 charged and thus responsible for the unintentional n -type conductivity as well as the nonstoichiometry of ZnO. The methodology can be extended to study oxygen-related point defects and their energetics in other technologically important oxide materials.

  2. Ultrathin FeOOH nanolayers with abundant oxygen vacancies on BiVO{sub 4} photoanodes for efficient water oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Beibei [State Key Laboratory for Oxo Synthesis and Selective Oxidation, National Engineering Research Center for Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou (China); State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou (China); Wang, Lei; Zhang, Yajun; Bi, Yingpu [State Key Laboratory for Oxo Synthesis and Selective Oxidation, National Engineering Research Center for Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou (China); Ding, Yong [State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou (China)

    2018-02-19

    Photoelectrochemical (PEC) water splitting is a promising method for storing solar energy in the form of hydrogen fuel, but it is greatly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, a facile solution impregnation method is developed for growing ultrathin (2 nm) highly crystalline β-FeOOH nanolayers with abundant oxygen vacancies on BiVO{sub 4} photoanodes. These exhibited a remarkable photocurrent density of 4.3 mA cm{sup -2} at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G), which is approximately two times higher than that of amorphous FeOOH fabricated by electrodeposition. Systematic studies reveal that the excellent PEC activity should be attributed to their ultrathin crystalline structure and abundant oxygen vacancies, which could effectively facilitate the hole transport/trapping and provide more active sites for water oxidation. (copyright 2018 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Oxygen vacancy effects in HfO2-based resistive switching memory: First principle study

    Directory of Open Access Journals (Sweden)

    Yuehua Dai

    2016-08-01

    Full Text Available The work investigated the shape and orientation of oxygen vacancy clusters in HfO2-base resistive random access memory (ReRAM by using the first-principle method based on the density functional theory. Firstly, the formation energy of different local Vo clusters was calculated in four established orientation systems. Then, the optimized orientation and charger conductor shape were identified by comparing the isosurface plots of partial charge density, formation energy, and the highest isosurface value of oxygen vacancy. The calculated results revealed that the [010] orientation was the optimal migration path of Vo, and the shape of system D4 was the best charge conductor in HfO2, which effectively influenced the SET voltage, formation voltage and the ON/OFF ratio of the device. Afterwards, the PDOS of Hf near Vo and total density of states of the system D4_010 were obtained, revealing the composition of charge conductor was oxygen vacancy instead of metal Hf. Furthermore, the migration barriers of the Vo hopping between neighboring unit cells were calculated along four different orientations. The motion was proved along [010] orientation. The optimal circulation path for Vo migration in the HfO2 super-cell was obtained.

  4. The effect of carbon and boron on the accumulation of vacancy-oxygen complexes in silicon

    International Nuclear Information System (INIS)

    Akhmetov, V.D.; Bolotov, V.V.

    1980-01-01

    By means of IR-absorption measurements the dose dependencies of the concentrations of vacancy-oxygen complexes (VO), interstitial oxygen atoms (Osub(I)), substitutional carbon atoms (Csub(S)) and interstitial carbon-oxygen complexes (Csub(I)Osub(I)) in n- and p-type silicon irradiated with 1.1 MeV electrons have been investigated. The observed increase of the production rate of VO-complexes with the rise of carbon and boron atoms concentrations (these impurities act as sinks for silicon interstitial atoms) has been explained in terms of annihilation of the vacancies and interstitials on the oxygen atoms. The results obtained show that boron atoms are more effective sinks than carbon atoms for the interstitial silicon atoms. That seems to be connected not only with the higher probability of boron injection into interstitial position but also with the further capture of interstitial silicon atoms on the interstitial boron, i.e. with the interstitial cluster formation. (author)

  5. Manipulating multiple order parameters via oxygen vacancies: The case of E u0.5B a0.5Ti O3 -δ

    Science.gov (United States)

    Li, Weiwei; He, Qian; Wang, Le; Zeng, Huizhong; Bowlan, John; Ling, Langsheng; Yarotski, Dmitry A.; Zhang, Wenrui; Zhao, Run; Dai, Jiahong; Gu, Junxing; Shen, Shipeng; Guo, Haizhong; Pi, Li; Wang, Haiyan; Wang, Yongqiang; Velasco-Davalos, Ivan A.; Wu, Yangjiang; Hu, Zhijun; Chen, Bin; Li, Run-Wei; Sun, Young; Jin, Kuijuan; Zhang, Yuheng; Chen, Hou-Tong; Ju, Sheng; Ruediger, Andreas; Shi, Daning; Borisevich, Albina Y.; Yang, Hao

    2017-09-01

    Controlling functionalities, such as magnetism or ferroelectricity, by means of oxygen vacancies (VO) is a key issue for the future development of transition-metal oxides. Progress in this field is currently addressed through VO variations and their impact on mainly one order parameter. Here we reveal a mechanism for tuning both magnetism and ferroelectricity simultaneously by using VO. Combining experimental and density-functional theory studies of E u0.5B a0.5Ti O3 -δ , we demonstrate that oxygen vacancies create T i3 +3 d1 defect states, mediating the ferromagnetic coupling between the localized Eu 4 f7 spins, and increase an off-center displacement of Ti ions, enhancing the ferroelectric Curie temperature. The dual function of Ti sites also promises a magnetoelectric coupling in the E u0.5B a0.5Ti O3 -δ .

  6. Vacancy identification in Co+ doped rutile TiO2 crystal with positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Ma Minyang; Qin Xiubo; Wang Baoyi; Wu Weiming

    2013-01-01

    Background: Room temperature Diluted Magnetic Semiconductor (DMS) is a critical path in the study of spin-electronic devices, but there are many disputes in the intrinsic properties and origin of the room temperature ferromagnetism. Positron annihilation spectroscopy (PAS) is a powerful technique for evaluating vacancy-type defects. Purpose: We aim to establish the relationship between the defect structure and ferromagnetism of the materials by analyzing the parameters of positron annihilation. Methods: Co-doped rutile TiO 2 films were synthesized by ion implantation and extensively studied by variable energy positron annihilation Doppler broadening spectroscopy (DBS) and coincidence Doppler broadening (CDB) measurements with variable energy slow positron beam for identification of the vacancies. Results: The results of DBS showed that a newly formed type of vacancy could be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy (Vo) complex Ti-Co-Vo and/or Ti-Vo were formed with Co ions implantation and the vacancy concentration increased with increasing dopant dose. Conclusion: We identify that the generation of Ti-Vo and/or Ti-Co-Vo vacancy complex are induced by the existence of excess Ti 3d electrons around the oxygen vacancy. (authors)

  7. Vacancy identification in Co+ doped rutile TiO2 crystal with positron annihilation spectroscopy

    Science.gov (United States)

    Qin, X. B.; Zhang, P.; Liang, L. H.; Zhao, B. Z.; Yu, R. S.; Wang, B. Y.; Wu, W. M.

    2011-01-01

    Co-doped rutile TiO2 films were synthesized by ion implantation. Variable energy positron annihilation Doppler broadening spectroscopy and coincidence Doppler broadening measurements were performed for identification of the vacancies. A newly formed type of vacancy can be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy (VO) complex Ti-Co-VO and/or Ti-VO are formed with Co ions implantation and the vacancy concentration is increased with increase of dopant dose.

  8. Electric-Field Control of Oxygen Vacancies and Magnetic Phase Transition in a Cobaltite/Manganite Bilayer

    Science.gov (United States)

    Cui, B.; Song, C.; Li, F.; Zhong, X. Y.; Wang, Z. C.; Werner, P.; Gu, Y. D.; Wu, H. Q.; Saleem, M. S.; Parkin, S. S. P.; Pan, F.

    2017-10-01

    Manipulation of oxygen vacancies (VO ) in single oxide layers by varying the electric field can result in significant modulation of the ground state. However, in many oxide multilayers with strong application potentials, e.g., ferroelectric tunnel junctions and solid-oxide fuel cells, understanding VO behavior in various layers under an applied electric field remains a challenge, owing to complex VO transport between different layers. By sweeping the external voltage, a reversible manipulation of VO and a corresponding fixed magnetic phase transition sequence in cobaltite/manganite (SrCoO3 -x/La0.45Sr0.55MnO3 -y ) heterostructures are reported. The magnetic phase transition sequence confirms that the priority of electric-field-induced VO formation or annihilation in the complex bilayer system is mainly determined by the VO formation energies and Gibbs free-energy differences, which is supported by theoretical analysis. We not only realize a reversible manipulation of the magnetic phase transition in an oxide bilayer but also provide insight into the electric-field control of VO engineering in heterostructures.

  9. Stoichiometric and Oxygen-Deficient VO2 as Versatile Hole Injection Electrode for Organic Semiconductors.

    Science.gov (United States)

    Fu, Keke; Wang, Rongbin; Katase, Takayoshi; Ohta, Hiromichi; Koch, Norbert; Duhm, Steffen

    2018-03-28

    Using photoemission spectroscopy, we show that the surface electronic structure of VO 2 is determined by the temperature-dependent metal-insulator phase transition and the density of oxygen vacancies, which depends on the temperature and ultrahigh vacuum (UHV) conditions. The atomically clean and stoichiometric VO 2 surface is insulating at room temperature and features an ultrahigh work function of up to 6.7 eV. Heating in UHV just above the phase transition temperature induces the expected metallic phase, which goes in hand with the formation of oxygen defects (up to 6% in this study), but a high work function >6 eV is maintained. To demonstrate the suitability of VO 2 as hole injection contact for organic semiconductors, we investigated the energy-level alignment with the prototypical organic hole transport material N, N'-di(1-naphthyl)- N, N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB). Evidence for strong Fermi-level pinning and the associated energy-level bending in NPB is found, rendering an Ohmic contact for holes.

  10. Oxygen vacancy chain and conductive filament formation in hafnia

    Science.gov (United States)

    Xue, Kan-Hao; Miao, Xiang-Shui

    2018-04-01

    The stability and aggregation mechanisms of oxygen vacancy chains are studied for hafnia using self-energy corrected density functional theory. While oxygen vacancies tend not to align along the c-axis of monoclinic HfO2, oxygen vacancy chains along a-axis and b-axis are energetically favorable, with cohesive energies of 0.05 eV and 0.03 eV per vacancy, respectively. Nevertheless, with an increase of the cross section area, intensive oxygen vacancy chains become much more stable in hafnia, which yields phase separation into Hf-clusters and HfO2. Compared with disperse single vacancy chains, intensive oxygen vacancy chains made of 4, 6, and 8 single vacancy chains are energetically more favorable by 0.17, 0.20, and 0.30 eV per oxygen vacancy, respectively. On the other hand, while a single oxygen vacancy chain exhibits a tiny electronic energy gap of around 0.5 eV, metallic conduction emerges for the intensive vacancy chain made of 8 single vacancy chains, which possesses a filament cross section area of ˜0.4 nm2. This sets a lower area limit for Hf-cluster filaments from metallic conduction point of view, but in real hafnia resistive RAM devices the cross section area of the filaments can generally be much larger (>5 nm2) for the sake of energy minimization. Our work sets up a bridge between oxygen vacancy ordering and phase separation in hafnia, and shows a clear trend of filament stabilization with larger dimensions. The results could explain the threshold switching phenomenon in hafnia when a small AFM tip was used as the top electrode, as well as the undesired multimode operation in resistive RAM cells with 3 nm-thick hafnia.

  11. Controlled manipulation of oxygen vacancies using nanoscale flexoelectricity

    Energy Technology Data Exchange (ETDEWEB)

    Das, Saikat [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Wang, Bo [Pennsylvania State Univ., University Park, PA (United States).Dept. of Materials Science and Engineering; Cao, Ye [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Inst. for; Rae Cho, Myung [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Jae Shin, Yeong [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Mo Yang, Sang [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Sookmyung Women' s Univ., Seoul (Republic of Korea). Dept. of Physics; Wang, Lingfei [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Kim, Minu [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Kalinin, Sergei V. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Inst. for Functional Imaging of Materials; Chen, Long-Qing [Pennsylvania State Univ., University Park, PA (United States).Dept. of Materials Science and Engineering; Noh, Tae Won [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy

    2017-09-20

    Oxygen vacancies, especially their distribution, are directly coupled to the electromagnetic properties of oxides and related emergent functionalities that have implications for device applications. Here using a homoepitaxial strontium titanate thin film, we demonstrate a controlled manipulation of the oxygen vacancy distribution using the mechanical force from a scanning probe microscope tip. By combining Kelvin probe force microscopy imaging and phase-field simulations, we show that oxygen vacancies can move under a stress-gradient-induced depolarisation field. When tailored, this nanoscale flexoelectric effect enables a controlled spatial modulation. In motion, the scanning probe tip thereby deterministically reconfigures the spatial distribution of vacancies. Finally, the ability to locally manipulate oxygen vacancies on-demand provides a tool for the exploration of mesoscale quantum phenomena and engineering multifunctional oxide devices.

  12. Tracking Oxygen Vacancies in Thin Film SOFC Cathodes

    Science.gov (United States)

    Leonard, Donovan; Kumar, Amit; Jesse, Stephen; Kalinin, Sergei; Shao-Horn, Yang; Crumlin, Ethan; Mutoro, Eva; Biegalski, Michael; Christen, Hans; Pennycook, Stephen; Borisevich, Albina

    2011-03-01

    Oxygen vacancies have been proposed to control the rate of the oxygen reduction reaction and ionic transport in complex oxides used as solid oxide fuel cell (SOFC) cathodes [1,2]. In this study oxygen vacancies were tracked, both dynamically and statically, with the combined use of scanned probe microscopy (SPM) and scanning transmission electron microscopy (STEM). Epitaxial films of La 0.8 Sr 0.2 Co O3 (L SC113) and L SC113 / LaSrCo O4 (L SC214) on a GDC/YSZ substrate were studied, where the latter showed increased electrocatalytic activity at moderate temperature. At atomic resolution, high angle annular dark field STEM micrographs revealed vacancy ordering in L SC113 as evidenced by lattice parameter modulation and EELS studies. The evolution of oxygen vacancy concentration and ordering with applied bias and the effects of bias cycling on the SOFC cathode performance will be discussed. Research is sponsored by the of Materials Sciences and Engineering Division, U.S. DOE.

  13. Molecular dynamics simulations of ferroelectric domain formation by oxygen vacancy

    Science.gov (United States)

    Zhu, Lin; You, Jeong Ho; Chen, Jinghong; Yeo, Changdong

    2018-05-01

    An oxygen vacancy, known to be detrimental to ferroelectric properties, has been investigated numerically for the potential uses to control ferroelectric domains in films using molecular dynamics simulations based on the first-principles effective Hamiltonian. As an electron donor, an oxygen vacancy generates inhomogeneous electrostatic and displacement fields which impose preferred polarization directions near the oxygen vacancy. When the oxygen vacancies are placed at the top and bottom interfaces, the out-of-plane polarizations are locally developed near the interfaces in the directions away from the interfaces. These polarizations from the interfaces are in opposite directions so that the overall out-of-plane polarization becomes significantly reduced. In the middle of the films, the in-plane domains are formed with containing 90° a 1/a 2 domain walls and the films are polarized along the [1 1 0] direction even when no electric field is applied. With oxygen vacancies placed at the top interface only, the films exhibit asymmetric hysteresis loops, confirming that the oxygen vacancies are one of the possible sources of ferroelectric imprint. It has been qualitatively demonstrated that the domain structures in the imprint films can be turned on and off by controlling an external field along the thickness direction. This study shows qualitatively that the oxygen vacancies can be utilized for tuning ferroelectric domain structures in films.

  14. Interplay of Cu and oxygen vacancy in optical transitions and screening of excitons in ZnO:Cu films

    International Nuclear Information System (INIS)

    Darma, Yudi; Rusydi, Andrivo; Seng Herng, Tun; Marlina, Resti; Fauziah, Resti; Ding, Jun

    2014-01-01

    We study room temperature optics and electronic structures of ZnO:Cu films as a function of Cu concentration using a combination of spectroscopic ellipsometry, photoluminescence, and ultraviolet-visible absorption spectroscopy. Mid-gap optical states, interband transitions, and excitons are observed and distinguishable. We argue that the mid-gap states are originated from interactions of Cu and oxygen vacancy (Vo). They are located below conduction band (Zn4s) and above valence band (O2p) promoting strong green emission and narrowing optical band gap. Excitonic states are screened and its intensities decrease upon Cu doping. Our results show the importance of Cu and Vo driving the electronic structures and optical transitions in ZnO:Cu films

  15. Interplay of Cu and oxygen vacancy in optical transitions and screening of excitons in ZnO:Cu films

    Science.gov (United States)

    Darma, Yudi; Seng Herng, Tun; Marlina, Resti; Fauziah, Resti; Ding, Jun; Rusydi, Andrivo

    2014-02-01

    We study room temperature optics and electronic structures of ZnO:Cu films as a function of Cu concentration using a combination of spectroscopic ellipsometry, photoluminescence, and ultraviolet-visible absorption spectroscopy. Mid-gap optical states, interband transitions, and excitons are observed and distinguishable. We argue that the mid-gap states are originated from interactions of Cu and oxygen vacancy (Vo). They are located below conduction band (Zn4s) and above valence band (O2p) promoting strong green emission and narrowing optical band gap. Excitonic states are screened and its intensities decrease upon Cu doping. Our results show the importance of Cu and Vo driving the electronic structures and optical transitions in ZnO:Cu films.

  16. Introduction of oxygen vacancies and fluorine into TiO2 nanoparticles by co-milling with PTFE

    International Nuclear Information System (INIS)

    Senna, Mamoru; Šepelák, Vladimir; Shi, Jianmin; Bauer, Benjamin; Feldhoff, Armin; Laporte, Vincent; Becker, Klaus-Dieter

    2012-01-01

    Solid-state processes of introducing oxygen vacancies and transference of fluorine to n-TiO 2 nanoparticles by co-milling with poly(tetrafluoroethylene) (PTFE) powder were examined by diffuse reflectance spectroscopy (DRS) of UV, visual, near- and mid-IR regions, thermal analyses (TG-DTA), energy-dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The broad absorption peak at around 8800 cm −1 (1140 nm) was attributed to the change in the electronic states, viz. electrons trapped at the oxygen vacancies (Vo) and d–d transitions of titanium ions. Incorporation of fluorine into n-TiO 2 was concentrated at the near surface region and amounted to ca. 40 at% of the total fluorine in PTFE, after co-milling for 3 h, as confirmed by the F1s XPS spectrum. The overall atomic ratio, F/Ti, determined by EDXS was 0.294. By combining these analytical results, a mechanism of the present solid state processes at the boundary between PTFE and n-TiO 2 was proposed. The entire process is triggered by the partial oxidative decomposition of PTFE. This is accompanied by the abstraction of oxygen atoms from the n-TiO 2 lattices. Loss of the oxygen atoms results in the formation of the diverse states of locally distorted coordination units of titania, i.e. TiO 6−n Vo n , located at the near surface region. This leads subsequent partial ligand exchange between F and O, to incorporate fluorine preferentially to the near surface region of n-TiO 2 particles, where local non-crystalline states predominate. - Graphical abstract: Scheme of the reaction processes: (a) pristine mixture, (b) oxygen abstraction from TiO 2 and (c) fluorine migration from PTFE to TiO 2 . Highlights: Transfer of fluorine from PTFE to n-TiO 2 in a dry solid state process was confirmed. ► 40% of F in PTFE was incorporated to the near surface region of n-TiO 2 nanoparticles. ► The transfer process is

  17. Formation and Migration of Oxygen Vacancies in SrCoO3 and their effect on Oxygen Evolution Reactions

    KAUST Repository

    Tahini, Hassan A.; Tan, Xin; Schwingenschlö gl, Udo; Smith, Sean C.

    2016-01-01

    Perovskite SrCoO3 is a potentially useful material for promoting the electrocatalytic oxygen evolution reaction, with high activities predicted theoretically and observed experimentally for closely related doped perovskite materials. However, complete stoichiometric oxidation is very difficult to realize experimentally – in almost all cases there are significant fractions of oxygen vacancies present. Here, using first principles calculations we study oxygen vacancies in perovskite SrCoO3 from thermodynamic, electronic and kinetic points of view. We find that an oxygen vacancy donates two electrons to neighboring Co sites in the form of localized charge. The formation energy of a single vacancy is very low and estimated to be 1.26 eV in the dilute limit. We find that a vacancy is quite mobile with a migration energy of ~0.5 eV. Moreover, we predict that oxygen vacancies exhibit a tendency towards clustering which is in accordance with the material’s ability to form a variety of oxygen-deficient structures. These vacancies have a profound effect on the material’s ability to facilitate OER, increasing the overpotential from ~0.3 V for the perfect material to ~0.7 for defective surfaces. A moderate compressive biaxial strain (2%) is predicted here to increase the surface oxygen vacancy formation energy by ca. 30%, thus reducing the concentration of surface vacancies and thereby preserving the OER activity of the material.

  18. Formation and Migration of Oxygen Vacancies in SrCoO3 and their effect on Oxygen Evolution Reactions

    KAUST Repository

    Tahini, Hassan A.

    2016-07-18

    Perovskite SrCoO3 is a potentially useful material for promoting the electrocatalytic oxygen evolution reaction, with high activities predicted theoretically and observed experimentally for closely related doped perovskite materials. However, complete stoichiometric oxidation is very difficult to realize experimentally – in almost all cases there are significant fractions of oxygen vacancies present. Here, using first principles calculations we study oxygen vacancies in perovskite SrCoO3 from thermodynamic, electronic and kinetic points of view. We find that an oxygen vacancy donates two electrons to neighboring Co sites in the form of localized charge. The formation energy of a single vacancy is very low and estimated to be 1.26 eV in the dilute limit. We find that a vacancy is quite mobile with a migration energy of ~0.5 eV. Moreover, we predict that oxygen vacancies exhibit a tendency towards clustering which is in accordance with the material’s ability to form a variety of oxygen-deficient structures. These vacancies have a profound effect on the material’s ability to facilitate OER, increasing the overpotential from ~0.3 V for the perfect material to ~0.7 for defective surfaces. A moderate compressive biaxial strain (2%) is predicted here to increase the surface oxygen vacancy formation energy by ca. 30%, thus reducing the concentration of surface vacancies and thereby preserving the OER activity of the material.

  19. Localized versus itinerant states created by multiple oxygen vacancies in SrTiO3

    Science.gov (United States)

    Jeschke, Harald O.; Shen, Juan; Valentí, Roser

    2015-02-01

    Oxygen vacancies in strontium titanate surfaces (SrTiO3) have been linked to the presence of a two-dimensional electron gas with unique behavior. We perform a detailed density functional theory study of the lattice and electronic structure of SrTiO3 slabs with multiple oxygen vacancies, with a main focus on two vacancies near a titanium dioxide terminated SrTiO3 surface. We conclude based on total energies that the two vacancies preferably inhabit the first two layers, i.e. they cluster vertically, while in the direction parallel to the surface, the vacancies show a weak tendency towards equal spacing. Analysis of the nonmagnetic electronic structure indicates that oxygen defects in the surface TiO2 layer lead to population of Ti {{t}2g} states and thus itinerancy of the electrons donated by the oxygen vacancy. In contrast, electrons from subsurface oxygen vacancies populate Ti eg states and remain localized on the two Ti ions neighboring the vacancy. We find that both the formation of a bound oxygen-vacancy state composed of hybridized Ti 3eg and 4p states neighboring the oxygen vacancy as well as the elastic deformation after extracting oxygen contribute to the stabilization of the in-gap state.

  20. Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3

    International Nuclear Information System (INIS)

    Schie, Marcel; Marchewka, Astrid; Waser, Rainer; Müller, Thomas; De Souza, Roger A

    2012-01-01

    A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO 3 ). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO 3 was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

  1. Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3.

    Science.gov (United States)

    Schie, Marcel; Marchewka, Astrid; Müller, Thomas; De Souza, Roger A; Waser, Rainer

    2012-12-05

    A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO(3)). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO(3) was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

  2. Role of oxygen vacancies in anodic TiO2 thin films

    International Nuclear Information System (INIS)

    Tit, N.; Halley, J.W.

    1992-05-01

    Defects play an important role in the electronic and optical properties of amorphous solids in general. Here we present both experimental and theoretical investigations on the nature and origin of defect states in anodic rutile TiO 2 thin films (of thickness 5nm to 20nm). There is experimental evidence that the observed gap state at 0.7eV below the edge of conduction-band is due to an oxygen vacancy. For this reason, oxygen vacancies are used in our model. A comparison of the calculated bulk-photoconductivity to photospectroscopy experiment reveals that the films have bulk-like transport properties. On the other hand a fit of the surface density of states to the scanning tunneling microscopy (STM) on the (001) surfaces has suggested a surface defect density of 5% of oxygen vacancies. To resolve this discrepancy, we calculated the dc-conductivity where localization effects are included. Our results show an impurity band formation at about p c =9% of oxygen vacancies. We concluded that the gap states seen in STM are localized and the oxygen vacancies are playing the role of trapping centers (deep levels) in the studied films. (author). 15 refs, 5 figs

  3. Oxygen vacancies dependent phase transition of Y{sub 2}O{sub 3} films

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Pengfei; Zhang, Kan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Huang, Hao [Titanium Alloys Lab. Beijing Institute of Aeronautical Materials, Beijing 81-15 100095 (China); Wen, Mao, E-mail: Wenmao225@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Li, Quan; Zhang, Wei; Hu, Chaoquan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Zheng, Weitao, E-mail: WTZheng@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Automotive Simulation and Control and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China)

    2017-07-15

    Highlights: • Oxygen vacancies for Y{sub 2}O{sub 3} films increase monotonously with increasing T{sub s}. • Oxygen vacancies can promote the nucleation of monoclinic phase. • That monoclinic phase with oxygen deficiency is not thermodynamic stable at high temperature. • Phase transition from monoclinic to oxygen defective occurs at high concentrations of oxygen vacancies. • High hardness just appears in Y{sub 2}O{sub 3} films with mixed phase configurations. - Abstract: Y{sub 2}O{sub 3} films have great application potential in high-temperature metal matrix composite and nuclear engineering, used as interface diffusion and reaction barrier coating owing to their excellent thermal and chemical stability, high melting point and extremely negative Gibbs formation energy, and thus their structural and mechanical properties at elevated temperature are especially important. Oxygen vacancies exist commonly in yttrium oxide (Y{sub 2}O{sub 3}) thin films and act strongly on the phase structure and properties, but oxygen vacancies dependent phase transition at elevated temperature has not been well explored yet. Y{sub 2}O{sub 3} thin films with different oxygen vacancy concentrations have been achieved by reactive sputtering through varying substrate temperature (T{sub s}), in which oxygen vacancies increase monotonously with increasing T{sub s}. For as-deposited Y{sub 2}O{sub 3} films, oxygen vacancies present at high T{sub s} can promote the nucleation of monoclinic phase, meanwhile, high T{sub s} can induce the instability of monoclinic phase. Thus their competition results in forming mixed phases of cubic and monoclinic at high T{sub s}. During vacuum annealing at 1000 °C, a critical oxygen vacancy concentration is observed, below which phase transition from monoclinic to cubic takes place, and above which phase transfer from monoclinic to the oxygen defective phase (ICDD file no. 39-1063), accompanying by stress reversal from compressive to tensile and

  4. Interaction of oxygen vacancies in yttrium germanates

    KAUST Repository

    Wang, Hao

    2012-01-01

    Forming a good Ge/dielectric interface is important to improve the electron mobility of a Ge metal oxide semiconductor field-effect transistor. A thin yttrium germanate capping layer can improve the properties of the Ge/GeO 2 system. We employ electronic structure calculations to investigate the effect of oxygen vacancies in yttrium-doped GeO 2 and the yttrium germanates Y 2Ge 2O 7 and Y 2GeO 5. The calculated densities of states indicate that dangling bonds from oxygen vacancies introduce in-gap states, but the system remains insulating. However, yttrium-doped GeO 2 becomes metallic under oxygen deficiency. Y-doped GeO 2, Y 2Ge 2O 7 and Y 2GeO 5 are calculated to be oxygen substoichiometric under low Fermi energy conditions. The use of yttrium germanates is proposed as a way to effectively passivate the Ge/dielectric interface. This journal is © 2012 the Owner Societies.

  5. Improving the Accuracy of Predicting Maximal Oxygen Consumption (VO2pk)

    Science.gov (United States)

    Downs, Meghan E.; Lee, Stuart M. C.; Ploutz-Snyder, Lori; Feiveson, Alan

    2016-01-01

    Maximal oxygen (VO2pk) is the maximum amount of oxygen that the body can use during intense exercise and is used for benchmarking endurance exercise capacity. The most accurate method to determineVO2pk requires continuous measurements of ventilation and gas exchange during an exercise test to maximal effort, which necessitates expensive equipment, a trained staff, and time to set-up the equipment. For astronauts, accurate VO2pk measures are important to assess mission critical task performance capabilities and to prescribe exercise intensities to optimize performance. Currently, astronauts perform submaximal exercise tests during flight to predict VO2pk; however, while submaximal VO2pk prediction equations provide reliable estimates of mean VO2pk for populations, they can be unacceptably inaccurate for a given individual. The error in current predictions and logistical limitations of measuring VO2pk, particularly during spaceflight, highlights the need for improved estimation methods.

  6. Correlated lifetimes of free paraexcitons and excitons trapped at oxygen vacancies in cuprous oxide

    International Nuclear Information System (INIS)

    Koirala, Sandhaya; Naka, Nobuko; Tanaka, Koichiro

    2013-01-01

    We have studied transients of luminescence due to free excitons and excitons trapped at oxygen vacancies in cuprous oxide. We find that both trapped and free paraexcitons have lifetime dependent on temperature and on the oxygen concentration. By using samples containing much less copper vacancies relative to oxygen vacancies, we find out the direct correlation between the free paraexciton lifetime and trapped exciton lifetime. - Highlights: ► We have investigated trapping of free excitons at oxygen vacancies in cuprous oxide. ► Lifetimes of free and trapped excitons exhibit correlative temperature dependence. ► Four-level model with the activation energy of 33 meV well explains the observation. ► Comparison is made using the four samples with different vacancy concentrations. ► We clarified the crucial role of the oxygen vacancy in shortening the lifetimes.

  7. Spin-dependent recombination involving oxygen-vacancy complexes in silicon

    OpenAIRE

    Franke, David P.; Hoehne, Felix; Vlasenko, Leonid S.; Itoh, Kohei M.; Brandt, Martin S.

    2014-01-01

    Spin-dependent relaxation and recombination processes in $\\gamma$-irradiated $n$-type Czochralski-grown silicon are studied using continuous wave (cw) and pulsed electrically detected magnetic resonance (EDMR). Two processes involving the SL1 center, the neutral excited triplet state of the oxygen-vacancy complex, are observed which can be separated by their different dynamics. One of the processes is the relaxation of the excited SL1 state to the ground state of the oxygen-vacancy complex, t...

  8. Probing of O2 vacancy defects and correlated magnetic, electrical and photoresponse properties in indium-tin oxide nanostructures by spectroscopic techniques

    Science.gov (United States)

    Ghosh, Shyamsundar; Dev, Bhupendra Nath

    2018-05-01

    Indium-tin oxide (ITO) 1D nanostructures with tunable morphologies i.e. nanorods, nanocombs and nanowires are grown on c-axis (0 0 0 1) sapphire (Al2O3) substrate in oxygen deficient atmosphere through pulsed laser deposition (PLD) technique and the effect of oxygen vacancies on optical, electrical, magnetic and photoresponse properties is investigated using spectroscopic methods. ITO nanostructures are found to be enriched with significant oxygen vacancy defects as evident from X-ray photoelectron and Raman spectroscopic analysis. Photoluminescence spectra exhibited intense mid-band blue emission at wavelength of region of 400-450 nm due to the electronic transition from conduction band maxima (CBM) to the singly ionized oxygen-vacancy (VO+) defect level within the band-gap. Interestingly, ITO nanostructures exhibited significant room-temperature ferromagnetism (RTFM) and the magnetic moment found proportional to concentration of VO+ defects which indicates VO+ defects are mainly responsible for the observed RTFM in nanostructures. ITO nanowires being enriched with more VO+ defects exhibited strongest RTFM as compared to other morphologies. Current voltage (I-V) characteristics of ITO nanostructures showed an enhancement of current under UV light as compared to dark which indicates such 1D nanostructure can be used as photovoltaic material. Hence, the study shows that there is ample opportunity to tailor the properties of ITOs through proper defect engineering's and such photosensitive ferromagnetic semiconductors might be promising for spintronic and photovoltaic applications.

  9. The effect of electron localization on the electronic structure and migration barrier of oxygen vacancies in rutile.

    Science.gov (United States)

    Zhu, Linggang; Hu, Qing-Miao; Yang, Rui

    2014-02-05

    By applying the on-site Coulomb interaction (Hubbard term U) to the Ti d orbital, the influence of electron localization on the electronic structure as well as the transport of oxygen vacancies (VO) in rutile was investigated. With U = 4.5 eV, the positions of defect states in the bandgap were correctly reproduced. The unbonded electrons generated by taking out one neutral oxygen atom are spin parallel and mainly localized on the Ti atoms near VO, giving rise to a magnetic moment of 2 μB, in agreement with the experimental finding. With regard to the migration barrier of VO, surprisingly, we found that U = 4.5 eV only changed the value of the energy barrier by ±0.15 eV, depending on the diffusion path. The most probable diffusion path (along [110]) is the same as that calculated by using the traditional GGA functional. To validate the GGA + U method itself, a hybrid functional with a smaller supercell was used, and the trend of the more probable diffusion path was not changed. In this regard, the traditional GGA functional might still be reliable in the study of intrinsic-defect transportation in rutile. Analyzing the atomic distortion and density of states of the transition states for different diffusion paths, we found that the anisotropy of the diffusion could be rationalized according to the various atomic relaxations and the different positions of the valence bands relative to the Fermi level of the transition states.

  10. The interaction of impurity oxygen in silicon with vacancies

    International Nuclear Information System (INIS)

    Aslanyan, A.A.; Babayan, S.A.; Eritsyan, G.N.; Kholodar, G.A.; Melkonyan, R.A.; Vinetskij, V.L.

    1981-01-01

    Silicon specimens irradiated with 50 MeV electrons, containing along with isolated oxygen atoms more complicated oxy-quasi-molecules of SiOsub(n) (n=1,2,3,...) type are investigated. At isochronal and isothermal annealing in the temperature range 300-350 deg C, besides the reaction of vacancy capturing by oxygen atoms with formation of A-centres, there occur more complicated reactions with participation of vacancies, A-centres, oxygen containing quasi-molecules, and a variety of sinks. The kinetics of the processing taking place at irradiation and annealing was studied with respect to the measurement of IR absorption spectra in the region 1-16 μm. A model is suggested to describe the observed processes that differ qualitatively from those taking place in specimens containing completely dissociated oxygen [ru

  11. Oxygen vacancies in oxides studied by annihilation of mono-energetic positrons

    Energy Technology Data Exchange (ETDEWEB)

    Hugenschmidt, Christoph; Pikart, Philip [ZWE FRM II, Technische Universitaet Muenchen, Lichtenbergstrasse 1, 85747 Garching (Germany); Physik-Department E21, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching (Germany); Schreckenbach, Klaus [Physik-Department E21, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching (Germany)

    2009-07-01

    Oxygen vacancies play a fundamental role for the material properties of various oxides, e.g. charge carrier density in high-Tc superconductors, magnetic properties of diluted magnetic semiconductors or paramagnetic properties of SiO{sub 2}. In this study, open volume defects in (metal) oxides are investigated by Doppler-broadening spectroscopy (DBS) of the positron annihilation. More detailed information about the chemical surrounding at the positron annihilation site is gained by additional coincident DBS experiments, where a signature of positrons annihilating with electrons from oxygen is observed. The mono-energetic positron beam at NEPOMUC was used which allows depth dependent measurements, and hence the investigation of thin oxide layers. Recent results for metallic oxides such as ZnO are presented and compared with various non-metallic oxides such as amorphous and crystalline SiO{sub 2}, oxygen terminated Si-surface, and ice. The role of neutral and charged oxygen vacancies and the application of the positron annihilation technique to study oxygen vacancies will be discussed.

  12. Oxygen Vacancy-Mediated ZnO Nanoparticle Photocatalyst for Degradation of Methylene Blue

    Directory of Open Access Journals (Sweden)

    Qiuping Zhang

    2018-02-01

    Full Text Available ZnO nanoparticles (NPs are synthesized by deoxidizing ZnO powder in a vacuum drying process. This process reduces the size of the NPs and increases the concentration of oxygen vacancies on their surfaces. ZnO NPs with sufficient oxygen vacancies are highly effective for the photodecomposition of methylene blue (MB dye in water under ultraviolet irradiation. The MB degradation efficiency exceeds 99 percent after 50 min of light irradiation, and the catalytic property of the NPs remains stable over several complete degradation cycles. It is revealed that the concentration of oxygen vacancies on the surface, and the photocatalytic activity, are both higher for smaller NPs. Oxygen vacancies reduce the recombination rate of photo-generated charge carriers by capturing the electrons and hence, improve the efficiency of redox reactions. In addition, a smaller particle size leads to a larger specific surface area and a higher photonic efficiency for the ZnO NPs.

  13. Enhanced Photocatalytic Activity of Vacuum-activated TiO2 Induced by Oxygen Vacancies.

    Science.gov (United States)

    Dong, Guoyan; Wang, Xin; Chen, Zhiwu; Lu, Zhenya

    2018-05-01

    TiO 2 (Degussa P25) photocatalysts harboring abundant oxygen vacancies (Vacuum P25) were manufactured using a simple and economic Vacuum deoxidation process. Control experiments showed that temperature and time of vacuum deoxidation had a significant effect on Vacuum P25 photocatalytic activity. After 240 min of visible light illumination, the optimal Vacuum P25 photocatalysts (vacuum deoxidation treated at 330 °C for 3 h) reach as high as 94% and 88% of photodegradation efficiency for rhodamine B (RhB) and tetracycline, respectively, which are around 4.5 and 4.9 times as that of pristine P25. The XPS, PL and EPR analyses indicated that the oxygen vacancies were produced in the Vacuum P25 during the vacuum deoxidation process. The oxygen vacancy states can produce vacancy energy level located below the conduction band minimum, which resulting in the bandgap narrowing, thus extending the photoresponse wavelength range of Vacuum P25. The positron annihilation analysis indicated that the concentrations ratio of bulk and surface oxygen vacancies could be adjusted by changing the vacuum deoxidation temperature and time. Decreasing the ratio of bulk and surface oxygen vacancies was shown to improve photogenerated electron-hole pair separation efficiency, which leads to an obvious enhancement of the visible photocatalytic activities of Vacuum P25. © 2017 The American Society of Photobiology.

  14. Unraveling the oxygen vacancy structures at the reduced Ce O2(111 ) surface

    Science.gov (United States)

    Han, Zhong-Kang; Yang, Yi-Zhou; Zhu, Beien; Ganduglia-Pirovano, M. Verónica; Gao, Yi

    2018-03-01

    Oxygen vacancies at ceria (Ce O2 ) surfaces play an essential role in catalytic applications. However, during the past decade, the near-surface vacancy structures at Ce O2(111 ) have been questioned due to the contradictory results from experiments and theoretical simulations. Whether surface vacancies agglomerate, and which is the most stable vacancy structure for varying vacancy concentration and temperature, are being heatedly debated. By combining density functional theory calculations and Monte Carlo simulations, we proposed a unified model to explain all conflicting experimental observations and theoretical results. We find a novel trimeric vacancy structure which is more stable than any other one previously reported, which perfectly reproduces the characteristics of the double linear surface oxygen vacancy clusters observed by STM. Monte Carlo simulations show that at low temperature and low vacancy concentrations, vacancies prefer subsurface sites with a local (2 × 2) ordering, whereas mostly linear surface vacancy clusters do form with increased temperature and degree of reduction. These results well explain the disputes about the stable vacancy structure and surface vacancy clustering at Ce O2(111 ) , and provide a foundation for the understanding of the redox and catalytic chemistry of metal oxides.

  15. Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics.

    Science.gov (United States)

    Liu, Jianqiao; Gao, Yinglin; Wu, Xu; Jin, Guohua; Zhai, Zhaoxia; Liu, Huan

    2017-08-10

    The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

  16. Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics

    Directory of Open Access Journals (Sweden)

    Jianqiao Liu

    2017-08-01

    Full Text Available The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

  17. Understanding Oxygen Vacancy Formation, Interaction, Transport, and Strain in SOFC Components via Combined Thermodynamics and First Principles Calculations

    Science.gov (United States)

    Das, Tridip

    Understanding of the vacancy formation, interaction, increasing its concentration and diffusion, and controlling its chemical strain will advance the design of mixed ionic and electronic conductor (MIEC) materials via element doping and strain engineering. This is especially central to improve the performance of the solid oxide fuel cell (SOFC), an energy conversion device for sustainable future. The oxygen vacancy concentration grows exponentially with the temperature at dilute vacancy concentration but not at higher concentration, or even decreases due to oxygen vacancy interaction and vacancy ordered phase change. This limits the ionic conductivity. Using density functional theory (DFT), we provided fundamental understanding on how oxygen vacancy interaction originates in one of the typical MIEC, La1-xSrxFeO3-delta (LSF). The vacancy interaction is determined by the interplay of the charge state of multi-valence ion (Fe), aliovalent doping (La/Sr ratio), the crystal structure, and the oxygen vacancy concentration and/or nonstoichiometry (delta). It was found excess electrons left due to the formation of a neutral oxygen vacancy get distributed to Fe directly connected to the vacancy or to the second nearest neighboring Fe, based on crystal field splitting of Fe 3d orbital in different Fe-O polyhedral coordination. The progressively larger polaron size and anisotropic shape changes with increasing Sr-content resulted in increasing oxygen vacancy interactions, as indicated by an increase in the oxygen vacancy formation energy above a critical delta threshold. This was consistent with experimental results showing that Sr-rich LSF and highly oxygen deficient compositions are prone to oxygen-vacancy-ordering-induced phase transformations, while Sr-poor and oxygen-rich LSF compositions are not. Since oxygen vacancy induced phase transformations, cause a decrease in the mobile oxygen vacancy site fraction (X), both delta and X were predicted as a function of

  18. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT).

    Science.gov (United States)

    Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

    2016-11-22

    The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La 3+ donor-doped, Fe 3+ acceptor-doped and La 3+ /Fe 3+ -co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

  19. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT

    Directory of Open Access Journals (Sweden)

    Christoph Slouka

    2016-11-01

    Full Text Available The different properties of acceptor-doped (hard and donor-doped (soft lead zirconate titanate (PZT ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

  20. Significant room-temperature ferromagnetism in porous ZnO films: The role of oxygen vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Xue; Liu, Huiyuan [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Sun, Huiyuan, E-mail: huiyuansun@126.com [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Liu, Lihu; Jia, Xiaoxuan [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China)

    2015-10-15

    Graphical abstract: - Highlights: • Porous ZnO films were deposited on porous anodic alumina substrates. • Significant ferromagnetism (FM) has been observed in porous ZnO films (110 emu/cm{sup 3}). • The strong magnetic anisotropy was observed in the porous ZnO films. • The origin of FM is attributed to the oxygen vacancy with a local magnetic moment. - Abstract: Pure porous ZnO films were prepared by direct current reactive magnetron sputtering on porous anodic alumina substrates. Remarkably large room-temperature ferromagnetism was observed in the films. The highest saturation moment along the out-of-plane direction was about 110 emu/cm{sup 3}. Experimental and theoretical results suggested that the oxygen vacancies and the unique porous structure of the films are responsible for the large ferromagnetism. There are two modes of coupling between oxygen vacancies in the porous ZnO films: (i) exchange interactions directly between the oxygen vacancies and (ii) with the mediation of conduction electrons. In addition, it was found that the magnetic moment of ZnO films can be changed by tuning the concentration of oxygen vacancies. These observations may be useful in the development of ZnO-based spintronics devices.

  1. Anisotropic chemical strain in cubic ceria due to oxygen-vacancy-induced elastic dipoles.

    Science.gov (United States)

    Das, Tridip; Nicholas, Jason D; Sheldon, Brian W; Qi, Yue

    2018-06-06

    Accurate characterization of chemical strain is required to study a broad range of chemical-mechanical coupling phenomena. One of the most studied mechano-chemically active oxides, nonstoichiometric ceria (CeO2-δ), has only been described by a scalar chemical strain assuming isotropic deformation. However, combined density functional theory (DFT) calculations and elastic dipole tensor theory reveal that both the short-range bond distortions surrounding an oxygen-vacancy and the long-range chemical strain are anisotropic in cubic CeO2-δ. The origin of this anisotropy is the charge disproportionation between the four cerium atoms around each oxygen-vacancy (two become Ce3+ and two become Ce4+) when a neutral oxygen-vacancy is formed. Around the oxygen-vacancy, six of the Ce3+-O bonds elongate, one of the Ce3+-O bond shorten, and all seven of the Ce4+-O bonds shorten. Further, the average and maximum chemical strain values obtained through tensor analysis successfully bound the various experimental data. Lastly, the anisotropic, oxygen-vacancy-elastic-dipole induced chemical strain is polarizable, which provides a physical model for the giant electrostriction recently discovered in doped and non-doped CeO2-δ. Together, this work highlights the need to consider anisotropic tensors when calculating the chemical strain induced by dilute point defects in all materials, regardless of their symmetry.

  2. A Unifying Perspective on Oxygen Vacancies in Wide Band Gap Oxides.

    Science.gov (United States)

    Linderälv, Christopher; Lindman, Anders; Erhart, Paul

    2018-01-04

    Wide band gap oxides are versatile materials with numerous applications in research and technology. Many properties of these materials are intimately related to defects, with the most important defect being the oxygen vacancy. Here, using electronic structure calculations, we show that the charge transition level (CTL) and eigenstates associated with oxygen vacancies, which to a large extent determine their electronic properties, are confined to a rather narrow energy range, even while band gap and the electronic structure of the conduction band vary substantially. Vacancies are classified according to their character (deep versus shallow), which shows that the alignment of electronic eigenenergies and CTL can be understood in terms of the transition between cavity-like localized levels in the large band gap limit and strong coupling between conduction band and vacancy states for small to medium band gaps. We consider both conventional and hybrid functionals and demonstrate that the former yields results in very good agreement with the latter provided that band edge alignment is taken into account.

  3. Simulation of the Atomic and Electronic Structure of Oxygen Vacancies and Polyvacancies in ZrO2

    Science.gov (United States)

    Perevalov, T. V.

    2018-03-01

    Cubic, tetragonal, and monoclinic phases of zirconium oxide with oxygen vacancies and polyvacancies are studied by quantum chemical modeling of the atomic and electronic structure. It is demonstrated that an oxygen vacancy in ZrO2 may act as both an electron trap and a hole one. An electron added to the ZrO2 structure with an oxygen vacancy is distributed between two neighboring Zr atoms and is a bonding orbital by nature. It is advantageous for each subsequent O vacancy to form close to the already existing ones; notably, one Zr atom has no more than two removed O atoms related to it. Defect levels from oxygen polyvacancies are distributed in the bandgap with preferential localization in the vicinity of the oxygen monovacancy level.

  4. Interaction of light with the ZnO surface: Photon induced oxygen “breathing,” oxygen vacancies, persistent photoconductivity, and persistent photovoltage

    International Nuclear Information System (INIS)

    Gurwitz, Ron; Cohen, Rotem; Shalish, Ilan

    2014-01-01

    ZnO surfaces adsorb oxygen in the dark and emit CO 2 when exposed to white light, reminiscent of the lungs of living creatures. We find that this exchange of oxygen with the ambient affects the integrity of the ZnO surface. Thus, it forms a basis for several interesting surface phenomena in ZnO, such as photoconductivity, photovoltage, and gas sensing, and has a role in ZnO electrical conduction. Using x-ray photoelectron spectroscopy on ZnO nanowires, we observed a decomposition of ZnO under white light and formation of oxygen-depleted surface, which explains photoconductivity by the electron donation of oxygen vacancies. Our findings suggest that the observed decomposition of the ZnO lattice may only take place due to photon-induced reduction of ZnO by carbon containing molecules (or carbo-photonic reduction), possibly from the ambient gas, accounting in a consistent way for both the reduced demands on the energy required for decomposition and for the observed emission of lattice oxygen in the form of CO 2 . The formation of oxygen-vacancy rich surface is suggested to induce surface delta doping, causing accumulation of electrons at the surface, which accounts for both the increase in conductivity and the flattening of the energy bands. Using surface photovoltage spectroscopy in ultra high vacuum, we monitored changes in the deep level spectrum. We observe a wide optical transition from a deep acceptor to the conduction band, which energy position coincides with the position of the so called “green luminescence” in ZnO. This green transition disappears with the formation of surface oxygen vacancies. Since the oxygen vacancies are donors, while the green transition involves surface acceptors, the results suggest that the initial emission of oxygen originates at the defect sites of the latter, thereby eliminating each other. This suggests that the green transition originates at surface Zn vacancy acceptors. Removing an oxygen atom from a Zn vacancy completes

  5. Interaction of light with the ZnO surface: Photon induced oxygen “breathing,” oxygen vacancies, persistent photoconductivity, and persistent photovoltage

    Energy Technology Data Exchange (ETDEWEB)

    Gurwitz, Ron; Cohen, Rotem; Shalish, Ilan, E-mail: shalish@ee.bgu.ac.il [Ben Gurion University, Beer Sheva 84105 (Israel)

    2014-01-21

    ZnO surfaces adsorb oxygen in the dark and emit CO{sub 2} when exposed to white light, reminiscent of the lungs of living creatures. We find that this exchange of oxygen with the ambient affects the integrity of the ZnO surface. Thus, it forms a basis for several interesting surface phenomena in ZnO, such as photoconductivity, photovoltage, and gas sensing, and has a role in ZnO electrical conduction. Using x-ray photoelectron spectroscopy on ZnO nanowires, we observed a decomposition of ZnO under white light and formation of oxygen-depleted surface, which explains photoconductivity by the electron donation of oxygen vacancies. Our findings suggest that the observed decomposition of the ZnO lattice may only take place due to photon-induced reduction of ZnO by carbon containing molecules (or carbo-photonic reduction), possibly from the ambient gas, accounting in a consistent way for both the reduced demands on the energy required for decomposition and for the observed emission of lattice oxygen in the form of CO{sub 2}. The formation of oxygen-vacancy rich surface is suggested to induce surface delta doping, causing accumulation of electrons at the surface, which accounts for both the increase in conductivity and the flattening of the energy bands. Using surface photovoltage spectroscopy in ultra high vacuum, we monitored changes in the deep level spectrum. We observe a wide optical transition from a deep acceptor to the conduction band, which energy position coincides with the position of the so called “green luminescence” in ZnO. This green transition disappears with the formation of surface oxygen vacancies. Since the oxygen vacancies are donors, while the green transition involves surface acceptors, the results suggest that the initial emission of oxygen originates at the defect sites of the latter, thereby eliminating each other. This suggests that the green transition originates at surface Zn vacancy acceptors. Removing an oxygen atom from a Zn vacancy

  6. Understanding the presence of vacancy clusters in ZnO from a kinetic perspective

    Science.gov (United States)

    Bang, Junhyeok; Kim, Youg-Sung; Park, C. H.; Gao, F.; Zhang, S. B.

    2014-06-01

    Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (VZn - Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of VZn compared to VO, more VZn-abundant clusters are formed than VO-abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (VZn - Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to VO donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations.

  7. Modeling of the structure and properties of oxygen vacancies in amorphous silica

    International Nuclear Information System (INIS)

    Mukhopadhyay, Sanghamitra; Sushko, Peter V.; Stoneham, A. Marshall; Shluger, Alexander L.

    2004-01-01

    We used an embedded cluster method to predict and characterize possible structural types of neutral and positively charged oxygen vacancies in amorphous silica. Defects were treated at 70 different oxygen sites of continuous random network amorphous structure generated using classical molecular dynamics. The neutral vacancies are characterized by a wide distribution of formation energies and structural parameters. Our modeling predicts the two major structural types of positively charged vacancies (E ' centers): dimer and dangling bond centers. The local structure of both types of centers depends on the medium range structure of the surrounding amorphous network. The majority of the dangling bond centers are unpuckered. We used structural 'fingerprints' derived from similar calculations of oxygen vacancy type centers in quartz and from experiment to find two other structural types of dangling bond centers: the puckered configuration and the back-projected configuration of E ' centers. In each case we find a distribution of both structural and EPR parameters. However, the average values of the EPR parameters for all dangling bond configurations are very similar. The structural criteria which favor the formation of different types of centers in the original amorphous structure are formulated in terms of the average Si-O distance of oxygen ion with its two neighboring silicon ions

  8. Pinning by oxygen vacancies in high-Tc superconductors

    International Nuclear Information System (INIS)

    Chudnovsky, E.M.

    1990-01-01

    It is shown that recent data of Murray et al. on spatial correlations in flux lattices of Bi-Sr-Ca-Cu-O (BSCCO) may be explained if one assumes that 1% of oxygen atoms in CuO 2 layers are missing. This estimate, being in remarkable agreement with that deduced by Kes and van der Beek from ac-susceptibility measurements, provides strong confidence that oxygen vacancies are the major source of pinning in BSCCO

  9. Fabrication of Ni-doped BiVO_4 semiconductors with enhanced visible-light photocatalytic performances for wastewater treatment

    International Nuclear Information System (INIS)

    Regmi, Chhabilal; Kshetri, Yuwaraj K.; Kim, Tae-Ho; Pandey, Ramesh Prasad; Ray, Schindra Kumar; Lee, Soo Wohn

    2017-01-01

    Highlights: • Synthesis of a Ni-doped BiVO_4 semiconductor photocatalyst with reduced band gap energy. • Ni-doped BiVO_4 provided efficient photocatalytic activity for ibuprofen degradation and E. coli and green tide deactivation. • DFT calculation and thermodynamic modeling to understand the underlying mechanism. - Abstract: A visible-light-driven Ni-doped BiVO_4 photocatalyst was synthesized using a microwave hydrothermal method. The nominal Ni doping amount of 1 wt% provided excellent photoactivity for a variety of water pollutants, such as ibuprofen (pharmaceutical), Escherichia coli (bacteria), and green tides (phytoplankton). Each Ni-doped BiVO_4 sample exhibits better performance than pure BiVO_4. The degradation of ibuprofen reaches 80% within 90 min, the deactivation of Escherichia coli reaches around 92% within 5 h, and the inactivation of green tide (Chlamydomonas pulsatilla) reaches 70% upon 60 min of the visible light irradiation. The first principle calculation and thermodynamic modeling revealed that Ni doping in the vanadium site gives the most stable configuration of the synthesized samples with the formation of an in-gap energy state and oxygen vacancies. The in-gap energy state and the oxygen vacancies serve as an electron-trapping center that decreases the migration time of the photogenerated carrier and increases the separation efficiency of electron-hole pairs, which are responsible for the observed efficient photocatalytic, anti-bacterial and anti-algal activity of the samples. These properties thus suggest potential applications of Ni-doped BiVO_4 as a multifunctional material in the field of wastewater treatment.

  10. Effect of annealing ambience on the formation of surface/bulk oxygen vacancies in TiO2 for photocatalytic hydrogen evolution

    Science.gov (United States)

    Hou, Lili; Zhang, Min; Guan, Zhongjie; Li, Qiuye; Yang, Jianjun

    2018-01-01

    The surface and bulk oxygen vacancy have a prominent effect on the photocatalytic performance of TiO2. In this study, TiO2 possessing different types and concentration of oxygen vacancies were prepared by annealing nanotube titanic acid (NTA) at various temperatures in air or vacuum atmosphere. TiO2 with the unitary bulk single-electron-trapped oxygen vacancies (SETOVs) formed when NTA were calcined in air. Whereas, TiO2 with both bulk and surface oxygen vacancies were obtained when NTA were annealed in vacuum. The series of TiO2 with different oxygen vacancies were systematically characterized by TEM, XRD, PL, XPS, ESR, and TGA. The PL and ESR analysis verified that surface oxygen vacancies and more bulk oxygen vacancies could form in vacuum atmosphere. Surface oxygen vacancies can trap electron and hinder the recombination of photo-generated charges, while bulk SETOVs act as the recombination center. The surface or bulk oxygen vacancies attributed different roles on the photo-absorbance and activity, leading that the sample of NTA-A400 displayed higher hydrogen evolution rate under UV light, whereas NTA-V400 displayed higher hydrogen evolution rate under visible light because bulk SETOVs can improve visible light absorption because sub-band formed by bulk SETOVs prompted the secondary transition of electron excited.

  11. Fabrication of Ni-doped BiVO{sub 4} semiconductors with enhanced visible-light photocatalytic performances for wastewater treatment

    Energy Technology Data Exchange (ETDEWEB)

    Regmi, Chhabilal [Department of Environmental and Biochemical Engineering, Sun Moon University, Chungnam 31460 (Korea, Republic of); Kshetri, Yuwaraj K. [Department of Advanced Materials Engineering, Sun Moon University, Chungnam 31460 (Korea, Republic of); Kim, Tae-Ho [Division of Mechanics and ICT Convergence Engineering, Sun Moon University, Chungnam 31460 (Korea, Republic of); Pandey, Ramesh Prasad [Institute of Biomolecule Reconstruction, Department of BT-Convergent Pharmaceutical Engineering, Sun Moon University, Chungnam 31460 (Korea, Republic of); Ray, Schindra Kumar [Department of Environmental and Biochemical Engineering, Sun Moon University, Chungnam 31460 (Korea, Republic of); Lee, Soo Wohn, E-mail: swlee@sunmoon.ac.kr [Department of Environmental and Biochemical Engineering, Sun Moon University, Chungnam 31460 (Korea, Republic of)

    2017-08-15

    Highlights: • Synthesis of a Ni-doped BiVO{sub 4} semiconductor photocatalyst with reduced band gap energy. • Ni-doped BiVO{sub 4} provided efficient photocatalytic activity for ibuprofen degradation and E. coli and green tide deactivation. • DFT calculation and thermodynamic modeling to understand the underlying mechanism. - Abstract: A visible-light-driven Ni-doped BiVO{sub 4} photocatalyst was synthesized using a microwave hydrothermal method. The nominal Ni doping amount of 1 wt% provided excellent photoactivity for a variety of water pollutants, such as ibuprofen (pharmaceutical), Escherichia coli (bacteria), and green tides (phytoplankton). Each Ni-doped BiVO{sub 4} sample exhibits better performance than pure BiVO{sub 4}. The degradation of ibuprofen reaches 80% within 90 min, the deactivation of Escherichia coli reaches around 92% within 5 h, and the inactivation of green tide (Chlamydomonas pulsatilla) reaches 70% upon 60 min of the visible light irradiation. The first principle calculation and thermodynamic modeling revealed that Ni doping in the vanadium site gives the most stable configuration of the synthesized samples with the formation of an in-gap energy state and oxygen vacancies. The in-gap energy state and the oxygen vacancies serve as an electron-trapping center that decreases the migration time of the photogenerated carrier and increases the separation efficiency of electron-hole pairs, which are responsible for the observed efficient photocatalytic, anti-bacterial and anti-algal activity of the samples. These properties thus suggest potential applications of Ni-doped BiVO{sub 4} as a multifunctional material in the field of wastewater treatment.

  12. A theoretical study of stability and vacancy replenishing of MoO{sub 3}(0 1 0) surfaces in oxygen atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Lei, Yan-Hua; Chen, Zhao-Xu, E-mail: zxchen@nju.edu.cn

    2016-01-15

    Graphical abstract: - Highlights: • Under normal experimental conditions perfect surface of MoO{sub 3}(0 1 0) is favorable. • Line defects along asymmetric oxygen direction in lean oxygen condition are favored. • Vacancy replenishing occurs on vacancies formed by terminal and asymmetrical oxygen. - Abstract: Oxygen vacancies on transition metal oxide surfaces are catalytically very important. The stability, shape and replenishing process of the vacancies are critical to understanding reactions happening on the surfaces. In this paper we investigate the stability of various defective MoO{sub 3}(0 1 0) surfaces and examine the influence of environmental oxygen on the stability as well as the active sites for the replenishing process. Our calculations reveal that the line oxygen defect along a (asymmetric oxygen) direction is thermodynamically most favorable at higher defect concentration whereas point defect surfaces are unfavorable. Under normal experimental conditions the perfect surface dominates the MoO{sub 3}(0 1 0). We show that for stoichiometric surfaces of any oxides (A{sub x}O{sub y}) the formation energy per vacancy controls the favorable defect shape (line or point defects). Calculations indicate that O{sub 2} can dissociate readily on the surfaces that double vacancies share one Mo atom. The replenishing process of the oxygen vacancies through O{sub 2} dissociation most likely occurs on the double-vacancy containing one terminal and one asymmetrical oxygen vacancies.

  13. Segregation and Migration of the Oxygen Vacancies in the 3 (111) Tilt Grain Boundaries of Ceria

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Fenglin [Univ. of Tennessee, Knoxville, TN (United States); Liu, Bin [Univ. of Tennessee, Knoxville, TN (United States); Zhang, Yanwen [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Weber, William J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-03-01

    In nanocrystalline materials, defect-grain boundary (GB) interaction plays a key role in determining the structure stability, as well as size-dependent ionic, electronic, magnetic and chemical properties. In this study, we systematically investigated using density functional theory segregation and migration of oxygen vacancies at the Σ3 [110] / (111) grain boundary of ceria. Three oxygen layers near the GB are predicted to be segregation sites for oxygen vacancies. Moreover, the presence of oxygen vacancies stabilizes this tilt GB at a low Fermi level and/or oxygen poor conditions. An atomic strain model was proposed to rationalize layer dependency of the relaxation energy for +2 charged oxygen vacancy. The structural origin of large relaxation energies at layers 1 and 2 was determined to be free-volume space that induces ion relaxation towards the GB. Our results not only pave the way for improving the oxygen transport near GBs of ceria, but also provide important insights into engineering the GB structure for better ionic, magnetic and chemical properties of nanocrystalline ceria.

  14. Strain-induced oxygen vacancies in ultrathin epitaxial CaMnO3 films

    Science.gov (United States)

    Chandrasena, Ravini; Yang, Weibing; Lei, Qingyu; Delgado-Jaime, Mario; de Groot, Frank; Arenholz, Elke; Kobayashi, Keisuke; Aschauer, Ulrich; Spaldin, Nicola; Xi, Xiaoxing; Gray, Alexander

    Dynamic control of strain-induced ionic defects in transition-metal oxides is considered to be an exciting new avenue towards creating materials with novel electronic, magnetic and structural properties. Here we use atomic layer-by-layer laser molecular beam epitaxy to synthesize high-quality ultrathin single-crystalline CaMnO3 films with systematically varying coherent tensile strain. We then utilize a combination of high-resolution soft x-ray absorption spectroscopy and bulk-sensitive hard x-ray photoemission spectroscopy in conjunction with first-principles theory and core-hole multiplet calculations to establish a direct link between the coherent in-plane strain and the oxygen-vacancy content. We show that the oxygen vacancies are highly mobile, which necessitates an in-situ-grown capping layer in order to preserve the original strain-induced oxygen-vacancy content. Our findings open the door for designing and controlling new ionically active properties in strongly-correlated transition-metal oxides.

  15. Chemical strain engineering of magnetism in PrVO3 thin films

    Science.gov (United States)

    Prellier, Wilfrid; Copie, Olivier; Varignon, Julien; Rotella, Helene; Steciuk, Gwladys; Boullay, Philippe; Pautrat, Alain; David, Adrian; Mercey, Bernard; Ghosez, Philippe

    Transition metal oxides having a perovskite structure present a wide range of functional properties ranging from insulator-to-metal, ferroelectricity, colossal magnetoresistance, high-temperature superconductivity and multiferroicity. Such systems are generally characterized by strong electronic correlations, complex phase diagrams and competing ground states. In addition, small perturbation induced by external stimuli (electric or magnetic field, temperature, strain, pressure..) may change structure, and ultimately modify the physical properties. Here, we synthetize an orthorhombic perovskite praseodymium vanadate (PrVO3), which is grown on strontium titanate substrate. We show that the control of the content of oxygen vacancies, the so-called chemical strain, can indeed result in unexpected properties. We further demonstrate that the Néel temperature can be tuned using the same substrate in agreement with first-principles calculations, and demonstrate that monitoring the concentration of oxygen vacancies through the oxygen partial pressure or the growth temperature can produce a substantial macroscopic tensile strain of a few percents.

  16. Oxygen vacancy defects in Ta{sub 2}O{sub 5} showing long-range atomic re-arrangements

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yuzheng; Robertson, John [Engineering Department, Cambridge University, Cambridge CB2 1PZ (United Kingdom)

    2014-03-17

    The structure, formation energy, and energy levels of the various oxygen vacancies in Ta{sub 2}O{sub 5} have been calculated using the λ phase model. The intra-layer vacancies give rise to unusual, long-range bonding rearrangements, which are different for each defect charge state. The 2-fold coordinated intra-layer vacancy is the lowest cost vacancy and forms a deep level 1.5 eV below the conduction band edge. The 3-fold intra-layer vacancy and the 2-fold inter-layer vacancy are higher cost defects, and form shallower levels. The unusual bonding rearrangements lead to low oxygen migration barriers, which are useful for resistive random access memory applications.

  17. Electro-oxidation of water on hematite: Effects of surface termination and oxygen vacancies investigated by first-principles

    DEFF Research Database (Denmark)

    Hellman, Anders; Iandolo, Beniamino; Wickman, Bjorn

    2015-01-01

    The oxygen evolution reaction on hydroxyl- and oxygen-terminated hematite was investigated using first-principle calculations within a theoretical electrochemical framework. Both pristine hematite and hematite containing oxygen vacancies were considered. The onset potential was determined to be 1...... on hematite occurs on the oxygen-terminated hematite, containing oxygen vacancies. (C) 2015 Elsevier B.V. All rights reserved....

  18. In Situ Observation of Oxygen Vacancy Dynamics and Ordering in the Epitaxial LaCoO3 System.

    Science.gov (United States)

    Jang, Jae Hyuck; Kim, Young-Min; He, Qian; Mishra, Rohan; Qiao, Liang; Biegalski, Michael D; Lupini, Andrew R; Pantelides, Sokrates T; Pennycook, Stephen J; Kalinin, Sergei V; Borisevich, Albina Y

    2017-07-25

    Vacancy dynamics and ordering underpin the electrochemical functionality of complex oxides and strongly couple to their physical properties. In the field of the epitaxial thin films, where connection between chemistry and film properties can be most clearly revealed, the effects related to oxygen vacancies are attracting increasing attention. In this article, we report a direct, real-time, atomic level observation of the formation of oxygen vacancies in the epitaxial LaCoO 3 thin films and heterostructures under the influence of the electron beam utilizing scanning transmission electron microscopy (STEM). In the case of LaCoO 3 /SrTiO 3 superlattice, the formation of the oxygen vacancies is shown to produce quantifiable changes in the interatomic distances, as well as qualitative changes in the symmetry of the Co sites manifested as off-center displacements. The onset of these changes was observed in both the [100] pc and [110] pc orientations in real time. Additionally, annular bright field images directly show the formation of oxygen vacancy channels along [110]pc direction. In the case of 15 u.c. LaCoO 3 thin film, we observe the sequence of events during beam-induced formation of oxygen vacancy ordered phases and find them consistent with similar processes in the bulk. Moreover, we record the dynamics of the nucleation, growth, and defect interaction at the atomic scale as these transformations happen. These results demonstrate that we can track dynamic oxygen vacancy behavior with STEM, generating atomic-level quantitative information on phase transformation and oxygen diffusion.

  19. Controlled oxygen vacancy induced p-type conductivity in HfO{sub 2-x} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Hildebrandt, Erwin; Kurian, Jose; Mueller, Mathis M.; Kleebe, Hans-Joachim; Alff, Lambert [Institute of Materials Science, Technische Universitaet Darmstadt, 64287 Darmstadt (Germany); Schroeder, Thomas [IHP, 15236 Frankfurt/Oder (Germany)

    2011-09-12

    We have synthesized highly oxygen deficient HfO{sub 2-x} thin films by controlled oxygen engineering using reactive molecular beam epitaxy. Above a threshold value of oxygen vacancies, p-type conductivity sets in with up to 6 times 10{sup 21} charge carriers per cm{sup 3}. At the same time, the band-gap is reduced continuously by more than 1 eV. We suggest an oxygen vacancy induced p-type defect band as origin of the observed behavior.

  20. Spin-dependent recombination involving oxygen-vacancy complexes in silicon

    Science.gov (United States)

    Franke, David P.; Hoehne, Felix; Vlasenko, Leonid S.; Itoh, Kohei M.; Brandt, Martin S.

    2014-05-01

    Spin-dependent relaxation and recombination processes in γ-irradiated n-type Czochralski-grown silicon are studied using continuous wave (cw) and pulsed electrically detected magnetic resonance (EDMR). Two processes involving the SL1 center, the neutral excited triplet state of the oxygen-vacancy complex, are observed which can be separated by their different dynamics. One of the processes is the relaxation of the excited SL1 state to the ground state of the oxygen-vacancy complex, the other a charge transfer between 31P donors and SL1 centers forming close pairs, as indicated by electrically detected electron double resonance. For both processes, the recombination dynamics is studied with pulsed EDMR techniques. We demonstrate the feasibility of true zero-field cw and pulsed EDMR for spin-1 systems and use this to measure the lifetimes of the different spin states of SL1 also at vanishing external magnetic field.

  1. Hydrogen peroxide reduction in the oxygen vacancies of ZnO nanotubes

    International Nuclear Information System (INIS)

    Peyghan, Ali Ahmadi; Laeen, Shima Parizad; Aslanzadeh, Saeed Amir; Moradi, Morteza

    2014-01-01

    The adsorption of a H 2 O 2 molecule on the pristine and O-vacancy defected ZnO nanotubes was investigated by means of density functional calculations. It was found that the molecule prefers to attach to two zinc atoms of the tube from its two oxygen atoms with the adsorption energy of 254.1 kJ/mol. Attachment of the H 2 O 2 to the wall of the tube does not have any significant influence on its highest occupied molecular orbital/lowest unoccupied molecular orbital gap (E g ). The presence of oxygen vacancy defect causes a decrease in the E g of the tube and, as a consequence, may cause an increase in the conductivity of the tube. The zinc atoms of the defect are more reactive toward H 2 O 2 reduction to H 2 O than perfect ones with the adsorption energy of 617.4 kJ/mol. During the adsorption process, the H 2 O 2 was reoriented in such a way that its O atom has diffused into vacancy site, so that O-O and O-H bonds of the molecule were dissociated and an H 2 O is formed. Thus, we think that ZnO-NTs may be a candidate for electrochemical reduction and detection of H 2 O 2 . - Highlights: • H 2 O 2 adsorption on pristine and O-vacancy defected ZnO nanotubes was studied by DFT. • H 2 O 2 does not have any significant influence on the gap of the tube. • Presence of oxygen vacancy defect causes a decrease in the gap of the tube. • ZnO nanotubes may be a candidate for electrochemical reduction and detection of H 2 O 2

  2. Vacancy distribution in nonstoichiometric vanadium monoxide

    International Nuclear Information System (INIS)

    Gusev, A.I.; Davydov, D.A.; Valeeva, A.A.

    2011-01-01

    Graphical abstract: Display Omitted Research highlights: → A certain fraction of vanadium atoms in disordered cubic vanadium monoxide VO y and ordered tetragonal phase V 52 O 64 is located in tetrahedral positions of a basic cubic lattice. → These positions are never occupied by any atoms in other strongly nonstoichiometric carbides, nitrides and oxides. → Both disordered and ordered structures of vanadium monoxide are characterized by the presence of short-range order of displacements in the oxygen sublattice and short-range order of substitution in the metal sublattice. → The short-range order of displacement is caused by the local displacements of O atoms from V (t) atoms occupying tetrahedral positions. The short-range order of substitution appears because V (t) atoms in the tetrahedral positions are always in the environment of four vacancies □ of the vanadium sublattice. - Abstract: Structural vacancy distribution in the crystal lattice of the tetragonal V 52 O 64 superstructure which is formed on the basis of disordered superstoichiometric cubic vanadium monoxide VO y ≡V x O z is experimentally determined and the presence of significant local atomic displacements and large local microstrains in a crystal lattice of real ordered phase is established. It is shown that the relaxation of local microstrains takes place owing to the basic disordered cubic phase grain refinement and a formation of ordered phase domains. The ordered phase domains grow in the direction from the boundaries to the centre of grains of the disordered basic cubic phase. Isothermal evolution at 970 K of the average domain size in ordered VO 1.29 vanadium monoxide is established. It is shown that the short-range order presents in a metal sublattice of disordered cubic VO y vanadium monoxide. The character of the short-range order is such that vanadium atoms occupying tetrahedral positions are in the environment of four vacant sites of the vanadium sublattice. This means that the

  3. Control of oxygen vacancies and Ce+3 concentrations in doped ceria nanoparticles via the selection of lanthanide element

    International Nuclear Information System (INIS)

    Shehata, N.; Meehan, K.; Hudait, M.; Jain, N.

    2012-01-01

    The effect of lanthanides that have positive association energies with oxygen vacancies, such as samarium and neodymium, and the elements with negative association energies, such as holmium and erbium, on ionization state of cerium and, consequentially, the oxygen vacancy concentration in doped ceria nanoparticles are investigated in this article. Structural and optical characterizations of the doped and undoped ceria nanoparticles, synthesized using chemical precipitation, are carried out using transmission electron microscopy, X-ray diffractometry, optical absorption spectroscopy, and fluorescence spectroscopy. It is deduced that the negative association energy dopants decrease the conversion of Ce +4 into Ce +3 and, hence, scavenge the oxygen vacancies, evidenced by the observed increase in the allowed direct bandgap, decrease in the integrated fluorescence intensity, and increased the size of doped nanoparticles. The opposite trends are obtained when the positive association dopants are used. It is concluded that the determining factor as to whether a lanthanide dopant in ceria acts as a generator or scavenger of oxygen vacancies in ceria nanoparticles is the sign of the association energy between the element and the oxygen vacancies. The ability to tailor the ionization state of cerium and the oxygen vacancy concentration in ceria has applications in a broad range of fields, which include catalysis, biomedicine, electronics, and environmental sensing.

  4. First-principles studies on vacancy-modified interstitial diffusion mechanism of oxygen in nickel, associated with large-scale atomic simulation techniques

    International Nuclear Information System (INIS)

    Fang, H. Z.; Shang, S. L.; Wang, Y.; Liu, Z. K.; Alfonso, D.; Alman, D. E.; Shin, Y. K.; Zou, C. Y.; Duin, A. C. T. van; Lei, Y. K.; Wang, G. F.

    2014-01-01

    This paper is concerned with the prediction of oxygen diffusivities in fcc nickel from first-principles calculations and large-scale atomic simulations. Considering only the interstitial octahedral to tetrahedral to octahedral minimum energy pathway for oxygen diffusion in fcc lattice, greatly underestimates the migration barrier and overestimates the diffusivities by several orders of magnitude. The results indicate that vacancies in the Ni-lattice significantly impact the migration barrier of oxygen in nickel. Incorporation of the effect of vacancies results in predicted diffusivities consistent with available experimental data. First-principles calculations show that at high temperatures the vacancy concentration is comparable to the oxygen solubility, and there is a strong binding energy and a redistribution of charge density between the oxygen atom and vacancy. Consequently, there is a strong attraction between the oxygen and vacancy in the Ni lattice, which impacts diffusion

  5. Oxygen vacancy-induced ferromagnetism in un-doped ZnO thin films

    Science.gov (United States)

    Zhan, Peng; Wang, Weipeng; Liu, Can; Hu, Yang; Li, Zhengcao; Zhang, Zhengjun; Zhang, Peng; Wang, Baoyi; Cao, Xingzhong

    2012-02-01

    ZnO films became ferromagnetic when defects were introduced by thermal-annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films and provides possibly an alternative way to prepare ferromagnetic ZnO films.

  6. Evidence for oxygen vacancy or ferroelectric polarization induced switchable diode and photovoltaic effects in BiFeO3 based thin films

    International Nuclear Information System (INIS)

    Guo Yiping; Guo Bing; Dong Wen; Li Hua; Liu Hezhou

    2013-01-01

    The diode and photovoltaic effects of BiFeO 3 and Bi 0.9 Sr 0.1 FeO 3−δ polycrystalline thin films were investigated by poling the films with increased magnitude and alternating direction. It was found that both electromigration of oxygen vacancies and polarization flipping are able to induce switchable diode and photovoltaic effects. For the Bi 0.9 Sr 0.1 FeO 3−δ thin films with high oxygen vacancy concentration, reversibly switchable diode and photovoltaic effects can be observed due to the electromigration of oxygen vacancies under an electric field much lower than its coercive field. However, for the pure BiFeO 3 thin films with lower oxygen vacancy concentration, the reversibly switchable diode and photovoltaic effect is hard to detect until the occurrence of polarization flipping. The switchable diode and photovoltaic effects can be explained well using the concepts of Schottky-like barrier-to-Ohmic contacts resulting from the combination of oxygen vacancies and polarization. The sign of photocurrent could be independent of the direction of polarization when the modulation of the energy band induced by oxygen vacancies is large enough to offset that induced by polarization. The photovoltaic effect induced by the electromigration of oxygen vacancies is unstable due to the diffusion of oxygen vacancies or the recombination of oxygen vacancies with hopping electrons. Our work provides deep insights into the nature of diode and photovoltaic effects in ferroelectric films, and will facilitate the advanced design of switchable devices combining spintronic, electronic, and optical functionalities. (paper)

  7. Physiological background of the change point in VO2 and the slow component of oxygen uptake kinetics.

    Science.gov (United States)

    Zoładź, J A; Korzeniewski, B

    2001-06-01

    It is generally believed that oxygen uptake during incremental exercise--until VO2max, increases linearly with power output (see eg. Astrand & Rodahl, 1986). On the other hand, it is well established that the oxygen uptake reaches a steady state only during a low power output exercise, but during a high power output exercise, performed above the lactate threshold (LT), the oxygen uptake shows a continuous increase until the end of the exercise. This effect has been called the slow component of VO2 kinetics (Whipp & Wasserman, 1972). The presence of a slow component in VO2 kinetics implies that during an incremental exercise test, after the LT has been exceeded, the VO2 to power output relationship has to become curvilinear. Indeed, it has recently been shown that during the incremental exercise, the exceeding of the power output, at which blood lactate begins to accumulate (LT), causes a non-proportional increase in VO2 (Zoladz et al. 1995) which indicates a drop in muscle mechanical efficiency. The power output at which VO2 starts to rise non-proportionally to the power output has been called "the change point in VO2" (Zoladz et al. 1998). In this paper, the significance of the factors most likely involved in the physiological mechanism responsible for the change point in oxygen uptake (CP-VO2) and for the slow component of VO2 kinetics, including: increase of activation of additional muscle groups, intensification of the respiratory muscle activity, recruitment of type II muscle fibres, increase of muscle temperature, increase of the basal metabolic rate, lactate and hydrogen ion accumulation, proton leak through the inner mitochondrial membrane, slipping of the ATP synthase and a decrease in the cytosolic phosphorylation potential, are discussed. Finally, an original own model describing the sequence of events leading to the non-proportional increase of oxygen cost of work at a high exercise intensity is presented.

  8. Effects of oxygen vacancies on the structural and optical properties of β-Ga2O3.

    Science.gov (United States)

    Dong, Linpeng; Jia, Renxu; Xin, Bin; Peng, Bo; Zhang, Yuming

    2017-01-09

    The structural, electronic, and optical properties of β-Ga 2 O 3 with oxygen vacancies are studied by employing first-principles calculations based on density function theory. Based on the defects formation energies, we conclude the oxygen vacancies are most stable in their fully charge states. The electronic structures and optical properties of β-Ga 2 O 3 are calculated by Generalized Gradient Approximation + U formalisms with the Hubbard U parameters set 7.0 eV and 8.5 eV for Ga and O ions, respectively. The calculated bandgap is 4.92 eV, which is consistent with the experimental value. The static real dielectric constants of the defective structures are increased compared with the intrinsic one, which is attributed to the level caused by the Ga-4s states in the bandgap. Extra peaks are introduced in the absorption spectra, which are related to Ga-4s and O-2p states. Experimentally, β-Ga 2 O 3 films are deposited under different O 2 volume percentage with ratio-frequency magnetron sputtering method. The measured results indicate that oxygen vacancies can induce extra emission peaks in the photoluminescence spectrum, the location of these peaks are close to the calculated results. Extra O 2 can increase the formation energies of oxygen vacancies and thus reduce oxygen vacancies in β-Ga 2 O 3 .

  9. Oxygen vacancies as active sites for water dissociation on rutile TiO2(110)

    DEFF Research Database (Denmark)

    Schaub, R.; Thostrup, P.; Lopez, Nuria

    2001-01-01

    to dissociate H2O through the transfer of one proton to a nearby oxygen atom, forming two hydroxyl groups for every vacancy. The amount of water dissociation is limited by the density of oxygen vacancies present on the clean surface exclusively. The dissociation process sets in as soon as molecular water...

  10. High temperature thermoelectric properties of strontium titanate thin films with oxygen vacancy and niobium doping

    KAUST Repository

    Sarath Kumar, S. R.; Barasheed, Abeer Z.; Alshareef, Husam N.

    2013-01-01

    We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m-1 K-1, and the estimated figure of merit is 0.29 at 1000 K. © 2013 American Chemical Society.

  11. High temperature thermoelectric properties of strontium titanate thin films with oxygen vacancy and niobium doping

    KAUST Repository

    Sarath Kumar, S. R.

    2013-08-14

    We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m-1 K-1, and the estimated figure of merit is 0.29 at 1000 K. © 2013 American Chemical Society.

  12. Oxygen vacancy induced fast lithium storage and efficient organics photodegradation over ultrathin TiO{sub 2} nanolayers grafted graphene sheets

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Yu, E-mail: xieyu_121@163.com [Nanchang Hangkong University, Department of Material Chemistry, Nanchang, Jiangxi Province (China); Hu, Dongsheng [Nanchang Hangkong University, Department of Material Chemistry, Nanchang, Jiangxi Province (China); Liu, Lianjun, E-mail: liul@uwm.edu [University of Wisconsin-Milwaukee, Mechanical Engineering Department, Milwaukee, WI (United States); Zhou, Panpan; Xu, Jiangwei; Ling, Yun [Nanchang Hangkong University, Department of Material Chemistry, Nanchang, Jiangxi Province (China)

    2016-11-15

    Highlights: • Oxygen vacancy is tailored by adjusting the treatment conditions. • Unltrathin TiO{sub 2} nanolayers are grafted on the graphene sheets. • Oxygen vacancy is located on the surface of TiO{sub 2}/graphene treated by H{sub 2}. • Improved lithium storage and organic pollutants removal efficiency. - Abstract: In this work we have developed a unique structure of ultrathin (5 nm) TiO{sub 2} nanolayers grafted graphene nanosheets (TiO{sub 2}/G) and integrated oxygen vacancy (V{sub O}) into TiO{sub 2} to enhance its lithium storage and photocatalytic performances. The defective TiO{sub 2}/G was synthesized by a solvothermal and subsequent thermal treatment method. When treated in a H{sub 2} atmosphere, the resulting TiO{sub 2-x}/G(H{sub 2}) has lower crystallinity, smaller crystal size, richer surface V{sub O}, higher surface area, larger pore volume, and lower charge transfer resistance than that reduced by NaBH{sub 4} solid, i.e., TiO{sub 2-x}/G(NaBH{sub 4}). More importantly, the surface V{sub O} in the TiO{sub 2-x}/G(H{sub 2}) could remarkably inhibit the recombination of photogenerated electron-hole pairs compared with the bulk Vo in the TiO{sub 2-x}/G(NaBH{sub 4}). As a result, the combination of all the factors contributed to the superiority of TiO{sub 2-x}/G(H{sub 2}), which demonstrated not only 70% higher specific capacity, longer cycling performance (1000 cycles) and better rate capability for lithium-ion battery, but also higher photocatalytic activity and 1.5 times faster degradation rate for organic pollutants removal than TiO{sub 2-x}/G(NaBH{sub 4}). The findings in this work will benefit the fundamental understanding of TiO{sub 2}/G surface chemistry and advance the design and preparation of functional materials for energy storage and water treatment.

  13. Effect of germanium doping on the annealing characteristics of oxygen and carbon-related defects in Czochralski silicon

    International Nuclear Information System (INIS)

    Londos, C. A.; Andrianakis, A.; Sgourou, E. N.; Emtsev, V.; Ohyama, H.

    2010-01-01

    This paper is devoted to the annealing studies of defects produced in carbon-rich Ge-doped Czochralski-grown Si (Cz-Si) by 2 MeV electron irradiation. The annealing temperature of vacancy-oxygen (VO) complexes, carbon interstitial-oxygen interstitial (C i O i ), and carbon interstitial-carbon substitutional (C i C s ) pairs as well as the formation temperature of vacancy-two oxygen (VO 2 ) complexes are monitored as a function of Ge concentration. It has been established that the annealing of C i O i and C i C s defects remains practically unaffected by the Ge presence, whereas the annealing temperature of VO defects and the formation temperature of VO 2 complexes are substantially lowered at Ge concentrations larger than 1x10 19 cm -3 . The hydrostatic component of elastic strains introduced by Ge atoms in the Si crystal lattice was calculated. It appears to be very small, at least insufficient to exert a pronounced effect upon the annealing behavior of radiation-produced defects. This conclusion is in line with what is observed for the C i O i and C i C s species. In the case of VO, whose annealing process in Cz-Si is concurrently conducted by two reaction paths VO+O i →VO 2 and VO+Si I →O i , we suggest that the latter reaction in Ge-doped Cz-Si is enhanced by emitting self-interstitials (Si I ) from loosely bound self-interstitial clusters predominantly formed around Ge impurity atoms. As a result, the liberation of self-interstitials at lower annealing temperatures leads to an enhanced annealing of VO defects. An enhanced formation of VO 2 complexes at lower temperatures is also discussed in terms of other reactions running in parallel with the reaction VO+Si I →O i .

  14. Oxygen-vacancy defects on BaTiO3 (001) surface: a quantum chemical study

    International Nuclear Information System (INIS)

    Duque, Carlos; Stashans, Arvids

    2003-01-01

    A quantum-chemical study of technologically important BaTiO 3 crystal and oxygen-vacancy defects on its (001) surface is reported in the present work. The computations are made using a quantum-chemical method developed for periodic systems (crystals), which is based on the Hartree-Fock theory. The atomic rearrangement due to the surface creation is obtained for a pure BaTiO 3 by means of the periodic large unit cell (LUC) model and using an automated geometry optimisation procedure. The same technique is employed to study the electronic and structural properties of the material due to the presence of an O vacancy and F centre (two electrons trapped in an oxygen vacancy). The computations are carried out for both cubic and tetragonal lattices

  15. Oxygen vacancy doping of hematite analyzed by electrical conductivity and thermoelectric power measurements

    Science.gov (United States)

    Mock, Jan; Klingebiel, Benjamin; Köhler, Florian; Nuys, Maurice; Flohre, Jan; Muthmann, Stefan; Kirchartz, Thomas; Carius, Reinhard

    2017-11-01

    Hematite (α -F e2O3 ) is known for poor electronic transport properties, which are the main drawback of this material for optoelectronic applications. In this study, we investigate the concept of enhancing electrical conductivity by the introduction of oxygen vacancies during temperature treatment under low oxygen partial pressure. We demonstrate the possibility of tuning the conductivity continuously by more than five orders of magnitude during stepwise annealing in a moderate temperature range between 300 and 620 K. With thermoelectric power measurements, we are able to attribute the improvement of the electrical conductivity to an enhanced charge-carrier density by more than three orders of magnitude. We compare the oxygen vacancy doping of hematite thin films with hematite nanoparticle layers. Thereby we show that the dominant potential barrier that limits charge transport is either due to grain boundaries in hematite thin films or due to potential barriers that occur at the contact area between the nanoparticles, rather than the potential barrier within the small polaron hopping model, which is usually applied for hematite. Furthermore, we discuss the transition from oxygen-deficient hematite α -F e2O3 -x towards the magnetite F e3O4 phase of iron oxide at high density of vacancies.

  16. Deep vs shallow nature of oxygen vacancies and consequent n -type carrier concentrations in transparent conducting oxides

    Science.gov (United States)

    Buckeridge, J.; Catlow, C. R. A.; Farrow, M. R.; Logsdail, A. J.; Scanlon, D. O.; Keal, T. W.; Sherwood, P.; Woodley, S. M.; Sokol, A. A.; Walsh, A.

    2018-05-01

    The source of n -type conductivity in undoped transparent conducting oxides has been a topic of debate for several decades. The point defect of most interest in this respect is the oxygen vacancy, but there are many conflicting reports on the shallow versus deep nature of its related electronic states. Here, using a hybrid quantum mechanical/molecular mechanical embedded cluster approach, we have computed formation and ionization energies of oxygen vacancies in three representative transparent conducting oxides: In2O3 ,SnO2, and ZnO. We find that, in all three systems, oxygen vacancies form well-localized, compact donors. We demonstrate, however, that such compactness does not preclude the possibility of these states being shallow in nature, by considering the energetic balance between the vacancy binding electrons that are in localized orbitals or in effective-mass-like diffuse orbitals. Our results show that, thermodynamically, oxygen vacancies in bulk In2O3 introduce states above the conduction band minimum that contribute significantly to the observed conductivity properties of undoped samples. For ZnO and SnO2, the states are deep, and our calculated ionization energies agree well with thermochemical and optical experiments. Our computed equilibrium defect and carrier concentrations, however, demonstrate that these deep states may nevertheless lead to significant intrinsic n -type conductivity under reducing conditions at elevated temperatures. Our study indicates the importance of oxygen vacancies in relation to intrinsic carrier concentrations not only in In2O3 , but also in SnO2 and ZnO.

  17. Trapping of oxygen vacancies on twin walls of CaTiO3: a computer simulation study

    International Nuclear Information System (INIS)

    Calleja, Mark; Dove, Martin T; Salje, Ekhard K H

    2003-01-01

    We have studied the atomic structure of [001] 90 deg. rotation twin walls in orthorhombic CaTiO 3 (symmetry Pbnm) at low temperature (10 K) and their effects on oxygen vacancies. The wall thickness was found to be 2.3 nm at T || T c and it was found that it is energetically favourable for such vacancies to reside in the wall, particularly when bridging titania ions in the (001) plane. The binding energy of an oxygen vacancy in the wall with respect to the bulk is calculated to be ≤ 1.2 eV

  18. The synergistic effect of phase heterojunction and surface heterojunction to improve photocatalytic activity of VO •-TiO2: the co-catalytic effect of H3PW12O40

    Science.gov (United States)

    Li, Haiyan; Cai, Shengnan; Yang, Pengfei; Bai, Yan; Dang, Dongbin

    2018-06-01

    With nanotube titanic acid (abbreviated as NTA) and the 12-tungstophosphoric acid (H3PW12O40• xH2O, denoted as HPW) as start materials, respectively, according to a simple hydrothermal process in acid medium, we successfully prepared HPW modified VO •-TiO2 composite photocatalysts. During heat treatment companied by the transformation of NTA to TiO2, a kind of single-electron-trapped oxygen vacancy (VO •) could be formed contributing to the visible light absorption of catalysts. The morphology, phase and chemical structure, optical and electronic properties, and so on of the produced catalysts with various HPW loadings are characterized. The size range of synthesized photocatalyst nanoparticles are about 10 50 nm. Taking aqueous rhodamine B (RhB) dye as model pollutant, we carried out photocatalytic activity test of the achieved catalysts, revealing that the hybrid photocatalysts display significantly enhanced visible light-driven ( λ ≥ 420 nm) photocatalytic activity for degradation of RhB. Among various catalysts, HPWN-0.1-120 composite with nominal loading of 0.1 g HPW and heat treatment temperature of 120 °C possesses the highest photocatalytic performance in visible light, which is closely related to the co-effect of phase heterojunction of rutile/anatase, surface heterojunction of anatase/HPW, and oxygen vacancy (VO •). The two types of heterojunction promote greatly the separation efficiency of photoelectrons and photoholes and oxygen vacancy lures response of catalysts to visible light.

  19. Effects of hydration and oxygen vacancy on CO2 adsorption and activation on beta-Ga2O3(100).

    Science.gov (United States)

    Pan, Yun-xiang; Liu, Chang-jun; Mei, Donghai; Ge, Qingfeng

    2010-04-20

    The effects of hydration and oxygen vacancy on CO(2) adsorption on the beta-Ga(2)O(3)(100) surface have been studied using density functional theory slab calculations. Adsorbed CO(2) is activated on the dry perfect beta-Ga(2)O(3)(100) surface, resulting in a carbonate species. This adsorption is slightly endothermic, with an adsorption energy of 0.07 eV. Water is preferably adsorbed molecularly on the dry perfect beta-Ga(2)O(3)(100) surface with an adsorption energy of -0.56 eV, producing a hydrated perfect beta-Ga(2)O(3)(100) surface. Adsorption of CO(2) on the hydrated surface as a carbonate species is also endothermic, with an adsorption energy of 0.14 eV, indicating a slightly repulsive interaction when H(2)O and CO(2) are coadsorbed. The carbonate species on the hydrated perfect surface can be protonated by the coadsorbed H(2)O to a bicarbonate species, making the CO(2) adsorption exothermic, with an adsorption energy of -0.13 eV. The effect of defects on CO(2) adsorption and activation has been examined by creating an oxygen vacancy on the dry beta-Ga(2)O(3)(100) surface. The formation of an oxygen vacancy is endothermic, by 0.34 eV, with respect to a free O(2) molecule in the gas phase. Presence of the oxygen vacancy promoted the adsorption and activation of CO(2). In the most stable CO(2) adsorption configuration on the dry defective beta-Ga(2)O(3)(100) surface with an oxygen vacancy, one of the oxygen atoms of the adsorbed CO(2) occupies the oxygen vacancy site, and the CO(2) adsorption energy is -0.31 eV. Water favors dissociative adsorption at the oxygen vacancy site on the defective surface. This process is spontaneous, with a reaction energy of -0.62 eV. These results indicate that, when water and CO(2) are present in the adsorption system simultaneously, water will compete with CO(2) for the oxygen vacancy sites and impact CO(2) adsorption and conversion negatively.

  20. Ferromagnetism and half metallicity induced by oxygen vacancies in the double perovskite BaSrNiWO{sub 6}: DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Aharbil, Y. [Laboratoire de Chimie Physique des Matériaux LCPM, Faculté des Sciences Ben M' Sik, Casablanca (Morocco); Labrim, H. [Unité Science de la Matière/DERS/Centre National de l’Energie, des Sciences et des Techniques Nucléaires (CNESTEN), Rabat (Morocco); Benmokhtar, S.; Haddouch, M. Ait [Laboratoire de Chimie Physique des Matériaux LCPM, Faculté des Sciences Ben M' Sik, Casablanca (Morocco); Bahmad, L., E-mail: bahmad@fsr.ac.ma [Mohammed V University in Rabat, Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E. URAC-12, B.P. 1014, Rabat (Morocco); Belhaj, A. [LIRST, Département de Physique, Faculté Poly-disciplinaire, Université Sultan Moulay Slimane, Béni Mellal (Morocco); Ez-Zahraouy, H.; Benyoussef, A. [Mohammed V University in Rabat, Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E. URAC-12, B.P. 1014, Rabat (Morocco)

    2016-11-01

    Using the spin polarized density functional theory (DFT) and exploring the Plane-Wave Self-Consistent Field (PWscf) code implemented in Quantum-ESPRESSO package, we investigate the effect of the Oxygen vacancies (V{sub O}) and the Oxygen interstitial (O{sub i}) on the double perovskite BaSrNiWO{sub 6}. This deals with the magnetic ordering and the electronic structure in such a pure sample exhibiting the insulating anti-ferromagnetic (AFM) state. This study shows that the presence of oxygen deficient defects converts the insulating to half metal with ferromagnetic or anti-ferromagnetic states. The magnetic ordering in BaSrNiWO{sub 6−δ} depends on the position of the Oxygen vacancy in the unit cell. However, it has been shown that the Oxygen interstitial preserves the anti-ferromagnetic propriety. We have computed the formation energies of different positions of the Oxygen vacancy (V{sub O}) and the Oxygen interstitial (O{sub i}) in the BaSrNiWO{sub 6} compound. We showed that the formation of V{sub O} is easier and vice versa for the O{sub i} formation. The obtained results reveal(V{sub O}) and the Oxygen interstitial (O{sub i}) that the anti-ferromagnetic can be converted to ferromagnetic in the double perovskite BaSrNiWO{sub 6} induced by Oxygen vacancies V{sub O}. - Highlights: • We have studied the ferromagnetism and Half Metallicity in Double Perovskite BaSrNiWO{sub 6}. • We have applied the Ab-inito calculations using the DFT approach. • We showed the effects induced by Oxygen Vacancies and Oxygen interstitial. • We found that the magnetic ordering in BaSrNiWO{sub 6−δ} depends on the position of the Oxygen vacancy in the unit cell.

  1. First principle simulations on the effects of oxygen vacancy in HfO2-based RRAM

    Directory of Open Access Journals (Sweden)

    Yuehua Dai

    2015-01-01

    Full Text Available HfO2-based resistive random access memory (RRAM takes advantage of oxygen vacancy (V o defects in its principle of operation. Since the change in resistivity of the material is controlled by the level of oxygen deficiency in the material, it is significantly important to study the performance of oxygen vacancies in formation of conductive filament. Excluding effects of the applied voltage, the Vienna ab initio simulation package (VASP is used to investigate the orientation and concentration mechanism of the oxygen vacancies based on the first principle. The optimal value of crystal orientation [010] is identified by means of the calculated isosurface plots of partial charge density, formation energy, highest isosurface value, migration barrier, and energy band of oxygen vacancy in ten established orientation systems. It will effectively influence the SET voltage, forming voltage, and the ON/OFF ratio of the device. Based on the results of orientation dependence, different concentration models are established along crystal orientation [010]. The performance of proposed concentration models is evaluated and analyzed in this paper. The film is weakly conductive for the samples deposited in a mixture with less than 4.167at.% of V o contents, and the resistive switching (RS phenomenon cannot be observed in this case. The RS behavior improves with an increase in the V o contents from 4.167at.% to 6.25at.%; nonetheless, it is found difficult to switch to a stable state. However, a higher V o concentration shows a more favorable uniformity and stability for HfO2-based RRAM.

  2. Identification of the gallium vacancy-oxygen pair defect in GaN

    International Nuclear Information System (INIS)

    Son, N. T.; Hemmingsson, C. G.; Janzen, E.; Paskova, T.; Evans, K. R.; Usui, A.; Morishita, N.; Ohshima, T.; Isoya, J.; Monemar, B.

    2009-01-01

    Cation vacancies like V Ga , V Al and their complexes with oxygen are predicted to be abundant in III-nitrides and to play an important role in nonradiative recombination. Appearing in triple or double negatively charged states, they are not paramagnetic and have not so far been detected by magnetic resonance even under illumination. In this Brief Report, we demonstrate an efficient way to make cation vacancy defects in GaN detectable by electron paramagnetic resonance and present our identification of the V Ga O N pair in GaN which is the model material for the III-nitrides and their alloys.

  3. Microstructure evolution characteristics induced by oxygen vacancy generation in anatase TiO2 based resistive switching devices

    Science.gov (United States)

    Liu, Chen; Gao, Bin; Huang, Peng; Kang, Jinfeng

    2017-03-01

    In this work, first principle calculations are employed to study the microstructure characteristics of the anatase TiO2 resistive switching material associated with the generation of oxygen vacancy (V o) based nanofilaments during the switching process. The calculations indicate that both the magnéli phase Ti4O7 and V o-defect phase of anatase TiO2 may be formed with the generation of oxygen vacancies during the forming and SET processes. Based on the calculations, a new physical insight is proposed to clarify the microstructure evolution characteristics of the anatase TiO2 resistive switching material and the correlation with resistive switching behaviors. During the forming or SET process, the anatase TiO2 is first excited to a transition state with the generation of oxygen vacancies, then fully relaxes to a stable V o-defect state. This V o-defect state may either recover to the original state with the recombination of the oxygen vacancies, which causes the reversible resistive switching behavior, or further transform to a much more stable state—the magnéli phase Ti4O7, through a phase transition process with the generation of many more oxygen vacancies. The phase transition from V o- defective anatase phase to magnéli phase Ti4O7 causes the failure of the resistive switching due to the significantly reduced possibility of the reversible phase transition from the magnéli phase to the anatase phase, compared with the possibility of the recombination from the V o-defective anatase.

  4. Evidence of oxygen vacancy and possible intermediate gap state in layered α-MoO{sub 3} single-crystal nanobelts

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.Z., E-mail: tcccz@shu.edu.cn; Li, Y.; Tang, X.D.

    2016-01-15

    Multilayered meso-structured MoO{sub 3} nanobelts have been synthesized by thermally oxidizing a molybdenum chip in a reduced oxygen atmosphere, with a view to disclosing the existence of oxygen vacancy and understanding the mechanism behind the influence of oxygen vacancy on the electronic structure of molybdenum oxides. Based on the measurements from X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM), it is found that the as-grown sample is single-crystal α-MoO{sub 3} with a (001) preferred orientation, which shows an irregular belt-like morphology being composed of some ~20 nm single-crystal thin layers. The present sample includes a lot of oxygen vacancies in the lattice, as evidenced by the considerably reduced coordination number of the central Mo atoms from X-ray absorption spectra (XAS) as well as the red shift of the main Raman peaks. The existence of the oxygen vacancies are further tested by the photoluminescence (PL) results as the main emission peak shows an obvious red shift with the corresponding optical band gap reduced to 2.3 eV. Very importantly, an extra emission positioned at 738 nm (1.68 eV) is believed to originate from the recombination of the electrons from the intermediate band (IB) to the valence band (VB), and the formation of the IB in the gap is also caused by oxygen-ion vacancies.

  5. Effect of oxygen vacancies on the electronic and optical properties of tungsten oxide from first principles calculations

    Science.gov (United States)

    Mehmood, Faisal; Pachter, Ruth; Murphy, Neil R.; Johnson, Walter E.; Ramana, Chintalapalle V.

    2016-12-01

    In this work, we investigated theoretically the role of oxygen vacancies on the electronic and optical properties of cubic, γ-monoclinic, and tetragonal phases of tungsten oxide (WO3) thin films. Following the examination of structural properties and stability of the bulk tungsten oxide polymorphs, we analyzed band structures and optical properties, applying density functional theory (DFT) and GW (Green's (G) function approximation with screened Coulomb interaction (W)) methods. Careful benchmarking of calculated band gaps demonstrated the importance of using a range-separated functional, where results for the pristine room temperature γ-monoclinic structure indicated agreement with experiment. Further, modulation of the band gap for WO3 structures with oxygen vacancies was quantified. Dielectric functions for cubic WO3, calculated at both the single-particle, essentially time-dependent DFT, as well as many-body GW-Bethe-Salpeter equation levels, indicated agreement with experimental data for pristine WO3. Interestingly, we found that introducing oxygen vacancies caused appearance of lower energy absorptions. A smaller refractive index was indicated in the defective WO3 structures. These predictions could lead to further experiments aimed at tuning the optical properties of WO3 by introducing oxygen vacancies, particularly for the lower energy spectral region.

  6. Ultrafast atomic layer-by-layer oxygen vacancy-exchange diffusion in double-perovskite LnBaCo2O5.5+δ thin films.

    Science.gov (United States)

    Bao, Shanyong; Ma, Chunrui; Chen, Garry; Xu, Xing; Enriquez, Erik; Chen, Chonglin; Zhang, Yamei; Bettis, Jerry L; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qingyu

    2014-04-22

    Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln = Er, Pr; -0.5 atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism. The first principles density functional theory calculations indicate that hydrogen atoms are present in LnBCO as bound to oxygen forming O-H bonds. This unprecedented oscillation phenomenon provides the first direct experimental evidence of the layer by layer oxygen vacancy exchange diffusion mechanism.

  7. Factors determining the oxygen consumption rate (VO2) on-kinetics in skeletal muscles.

    Science.gov (United States)

    Korzeniewski, Bernard; Zoladz, Jerzy A

    2004-05-01

    Using a computer model of oxidative phosphorylation developed previously [Korzeniewski and Mazat (1996) Biochem. J. 319, 143-148; Korzeniewski and Zoladz (2001) Biophys. Chem. 92, 17-34], we analyse the effect of several factors on the oxygen-uptake kinetics, especially on the oxygen consumption rate (VO2) and half-transition time t(1/2), at the onset of exercise in skeletal muscles. Computer simulations demonstrate that an increase in the total creatine pool [PCr+/-Cr] (where Cr stands for creatine and PCr for phosphocreatine) and in glycolytic ATP supply lengthen the half-transition time, whereas increase in mitochondrial content, in parallel activation of ATP supply and ATP usage, in oxygen concentration, in proton leak, in resting energy demand, in resting cytosolic pH and in initial alkalization decrease this parameter. Theoretical studies show that a decrease in the activity of creatine kinase (CK) [displacement of this enzyme from equilibrium during on-transient (rest-to-work transition)] accelerates the first stage of the VO2 on-transient, but slows down the second stage of this transient. It is also demonstrated that a prior exercise terminated a few minutes before the principal exercise shortens the transition time. Finally, it is shown that at a given ATP demand, and under conditions where CK works near the thermodynamic equilibrium, the half-transition time of VO2 kinetics is determined by the amount of PCr that has to be transformed into Cr during rest-to-work transition; therefore any factor that diminishes the difference in [PCr] between rest and work at a given energy demand will accelerate the VO2 on-kinetics. Our conclusions agree with the general idea formulated originally by Easterby [(1981) Biochem. J. 199, 155-161] that changes in metabolite concentrations determine the transition times between different steady states in metabolic systems.

  8. First-Principles Study on the Structural and Electronic Properties of N Atoms Doped-Rutile TiO2 of Oxygen Vacancies

    Directory of Open Access Journals (Sweden)

    Zhong-Liang Zeng

    2015-01-01

    Full Text Available For the propose of considering the actual situation of electronic neutral, a simulation has been down on the basis of choosing the position of dual N and researching the oxygen vacancy. It is found that the reason why crystal material gets smaller is due to the emergence of impurity levels. By introducing the oxygen vacancy to the structure, the results show that while the oxygen vacancy is near the two nitrogen atoms which have a back to back position, its energy gets the lowest level and its structure gets the most stable state. From its energy band structure and density, the author finds that the impurity elements do not affect the migration of Fermi level while the oxygen vacancy has been increased. Instead of that, the conduction band of metal atoms moves to the Fermi level and then forms the N-type semiconductor material, but the photocatalytic activity is not as good as the dual N-doping state.

  9. Zinc vacancy and oxygen interstitial in ZnO revealed by sequential annealing and electron irradiation

    Science.gov (United States)

    Knutsen, K. E.; Galeckas, A.; Zubiaga, A.; Tuomisto, F.; Farlow, G. C.; Svensson, B. G.; Kuznetsov, A. Yu.

    2012-09-01

    By combining results from positron annihilation and photoluminescence spectroscopy with data from Hall effect measurements, the characteristic deep level emission centered at ˜1.75 eV and exhibiting an activation energy of thermal quenching of 11.5 meV is associated with the zinc vacancy. Further, a strong indication that oxygen interstitials act as a dominating acceptor is derived from the analysis of charge carrier losses induced by electron irradiation with variable energy below and above the threshold for Zn-atom displacement. We also demonstrate that the commonly observed green emission is related to an extrinsic acceptorlike impurity, which may be readily passivated by oxygen vacancies.

  10. Oxygen vacancy formation and migration in Sr- and Mg-doped LaGaO3: a density functional theory study

    International Nuclear Information System (INIS)

    Zhang Jie; Liang Er-Jun; Sun Qiang; Jia Yu

    2012-01-01

    Oxygen vacancy formation and migration in La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3−δ (LSGM) with various crystal symmetries (cubic, rhombohedral, orthorhombic, and monoclinic) are studied by employing first-principles calculations based on density functional theory (DFT). It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In our calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O 1 and O 2 oxygen sites. The migration energies along the migration pathway linking the two O 2 sites are obviously lower than those along the pathway linking the O 1 and O 2 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  11. The role of Ar plasma treatment in generating oxygen vacancies in indium tin oxide thin films prepared by the sol-gel process

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Deuk-Kyu [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seoul, 03722 (Korea, Republic of); Misra, Mirnmoy; Lee, Ye-Eun [Department of BioNano Technology, Gachon University, 1342 Seong-nam dae-ro, Seong-nam si, Gyeonggi-do, 13120 (Korea, Republic of); Baek, Sung-Doo [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seoul, 03722 (Korea, Republic of); Myoung, Jae-Min, E-mail: jmmyoung@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seoul, 03722 (Korea, Republic of); Lee, Tae Il, E-mail: t2.lee77@gachon.ac.kr [Department of BioNano Technology, Gachon University, 1342 Seong-nam dae-ro, Seong-nam si, Gyeonggi-do, 13120 (Korea, Republic of)

    2017-05-31

    Highlights: • Indium tin oxide thin film with about 41 nm thickness was obtained by the sol-gel process. • Thin film exhibited low resistivity. • Sheet resistance of thin film decreases with Ar plasma treatment time. • Ar plasma treatment on thin film does not alter the crystal structure and optical properties of the ITO thin-film. • There is no significant change in oxygen vacancies after 20 min of plasma treatment. - Abstract: Argon (Ar) plasma treatment was carried out to reduce the sheet resistance of indium tin oxide (ITO) thin films. The Ar plasma treatment did not cause any significant changes to the crystal structure, surface morphology, or optical properties of the ITO thin films. However, an X-ray photoelectron spectroscopy study confirmed that the concentration of oxygen vacancies in the film dramatically increased with the plasma treatment time. Thus, we concluded that the decrease in the sheet resistance was caused by the increase in the oxygen vacancy concentration in the film. Furthermore, to verify how the concentration of oxygen vacancies in the film increased with the Ar plasma treatment time, cumulative and continuous plasma treatments were conducted. The oxygen vacancies were found to be created by surface heating via the outward thermal diffusion of oxygen atoms from inside the film.

  12. The interplay between dopants and oxygen vacancies in the magnetism of V-doped TiO2

    KAUST Repository

    Grau-Crespo, Ricardo

    2011-08-03

    Density functional theory calculations indicate that the incorporation of V into Ti lattice positions of rutile TiO2 leads to magnetic V 4 + species, but the extension and sign of the coupling between dopant moments confirm that ferromagnetic order cannot be reached via low-concentration doping in the non-defective oxide. Oxygen vacancies can introduce additional magnetic centres, and we show here that one of the effects of vanadium doping is to reduce the formation energies of these defects. In the presence of both V dopants and O vacancies all the spins tend to align with the same orientation. We conclude that V doping favours the ferromagnetic behaviour of TiO2 not only by introducing spins associated with the dopant centres but also by increasing the concentration of oxygen vacancies with respect to the pure oxide. © 2001 IOP Publishing Ltd.

  13. The interplay between dopants and oxygen vacancies in the magnetism of V-doped TiO2

    KAUST Repository

    Grau-Crespo, Ricardo; Schwingenschlö gl, Udo

    2011-01-01

    Density functional theory calculations indicate that the incorporation of V into Ti lattice positions of rutile TiO2 leads to magnetic V 4 + species, but the extension and sign of the coupling between dopant moments confirm that ferromagnetic order cannot be reached via low-concentration doping in the non-defective oxide. Oxygen vacancies can introduce additional magnetic centres, and we show here that one of the effects of vanadium doping is to reduce the formation energies of these defects. In the presence of both V dopants and O vacancies all the spins tend to align with the same orientation. We conclude that V doping favours the ferromagnetic behaviour of TiO2 not only by introducing spins associated with the dopant centres but also by increasing the concentration of oxygen vacancies with respect to the pure oxide. © 2001 IOP Publishing Ltd.

  14. Relation of oxygen uptake to work rate in prepubertal healthy children - reference for VO2/W-slope and effect on cardiorespiratory fitness assessment.

    Science.gov (United States)

    Tompuri, Tuomo; Lintu, Niina; Laitinen, Tomi; Lakka, Timo A

    2017-08-09

    Exercise testing by cycle ergometer allows to observe the interaction between oxygen uptake (VO 2 ) and workload (W), and VO 2 /W-slope can be used as a diagnostic tool. Respectively, peak oxygen uptake (VO 2 PEAK ) can be estimated by maximal workload. We aim to determine reference for VO 2 /W-slope among prepubertal children and define agreement between estimated and measured VO 2 PEAK . A total of 38 prepubertal children (20 girls) performed a maximal cycle ergometer test with respiratory gas analysis. VO 2 /W-slopes were computed using linear regression. Agreement analysis by Bland and Altman for estimated and measured VO 2 PEAK was carried out including limits of agreement (LA). Determinants for VO 2 /W-slopes and estimation bias were defined. VO2/W-slope was in both girls and boys ≥9·4 and did not change with exercise level, but the oxygen cost of exercise was higher among physically more active children. Estimated VO 2 PEAK had 6·4% coefficient of variation, and LA varied from 13% underestimation to 13% overestimation. Bias had a trend towards underestimation along lean mass proportional VO 2 PEAK . The primary determinant for estimation bias was VO2/W-slope (β = -0·65; PW-slope among healthy prepubertal children were similar to those published for adults and among adolescents. Estimated and measured VO 2 PEAK should not be considered to be interchangeable because of the variation in the relationship between VO 2 and W. On other hand, variation in the relationship between VO 2 and W enables that VO 2 /W-slope can be used as a diagnostic tool. © 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

  15. Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films

    KAUST Repository

    Sarath Kumar, S. R.; Abutaha, Anas I.; Hedhili, Mohamed N.; Alshareef, Husam N.

    2012-01-01

    A detailed study of the role of oxygen vacancies in determining the effective mass and high temperature (300–1000 K) thermoelectricproperties of La-doped epitaxial SrTiO3 thin films is presented. It is observed that at intermediate temperatures, a transition from degenerate to non-degenerate behavior is observed in the Seebeck coefficient, but not electrical conductivity, which is attributed to heterogeneous oxygen non-stoichiometry. Heikes formula is found to be invalid for the films with oxygen vacancies. By fitting the spectroscopic ellipsometry (SE) data, obtained in the range 300–2100 nm, using a Drude-Lorentz dispersion relation with two Lorentz oscillators, the electrical and optical properties of the films are extracted. Using the excellent agreement between the transport properties extracted from SE modeling and direct electrical measurements, we demonstrate that an increase in concentration of oxygen vacancies results in a simultaneous increase of both carrier concentration and electron effective mass, resulting in a higher power factor.

  16. Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films

    KAUST Repository

    Sarath Kumar, S. R.

    2012-12-03

    A detailed study of the role of oxygen vacancies in determining the effective mass and high temperature (300–1000 K) thermoelectricproperties of La-doped epitaxial SrTiO3 thin films is presented. It is observed that at intermediate temperatures, a transition from degenerate to non-degenerate behavior is observed in the Seebeck coefficient, but not electrical conductivity, which is attributed to heterogeneous oxygen non-stoichiometry. Heikes formula is found to be invalid for the films with oxygen vacancies. By fitting the spectroscopic ellipsometry (SE) data, obtained in the range 300–2100 nm, using a Drude-Lorentz dispersion relation with two Lorentz oscillators, the electrical and optical properties of the films are extracted. Using the excellent agreement between the transport properties extracted from SE modeling and direct electrical measurements, we demonstrate that an increase in concentration of oxygen vacancies results in a simultaneous increase of both carrier concentration and electron effective mass, resulting in a higher power factor.

  17. Contributions of oxygen vacancies and titanium interstitials to band-gap states of reduced titania

    Science.gov (United States)

    Li, Jingfeng; Lazzari, Rémi; Chenot, Stéphane; Jupille, Jacques

    2018-01-01

    The spectroscopic fingerprints of the point defects of titanium dioxide remain highly controversial. Seemingly indisputable experiments lead to conflicting conclusions in which oxygen vacancies and titanium interstitials are alternately referred to as the primary origin of the Ti 3 d band-gap states. We report on experiments performed by electron energy loss spectroscopy whose key is the direct annealing of only the very surface of rutile TiO2(110 ) crystals and the simultaneous measurement of its temperature via the Bose-Einstein loss/gain ratio. By surface preparations involving reactions with oxygen and water vapor, in particular, under electron irradiation, vacancy- and interstitial-related band-gap states are singled out. Off-specular measurements reveal that both types of defects contribute to a unique charge distribution that peaks in subsurface layers with a common dispersive behavior.

  18. RGO/InVO4 hollowed-out nanofibers: Electrospinning synthesis and its application in photocatalysis

    International Nuclear Information System (INIS)

    Ma, Dong; Zhang, Yanxiang; Gao, Mengchun; Xin, Yanjun; Wu, Juan; Bao, Nan

    2015-01-01

    Graphical abstract: - Highlights: • RGO/InVO 4 hollow-out nanofibers were obtained by electrospinning method. • The properties of InVO 4 hollow-out nanofibers were deeply influenced by RGO. • RGO could reduce recombination of e − –h + pairs to improve photocatalytic activity. • Photo-induced h + and e − are the two main reactive species for RhB degradation. - Abstract: A composite of reduced graphene oxide (RGO) and InVO 4 nanofiber was successfully synthesized by an electrospinning technique. The as-collected fibers were calcined at 420 °C in air and then calcined at 550 °C in nitrogen gas to remove polyvinyl pyrrolidone (PVP), which could enable InVO 4 to crystallize and protect the RGO from oxidation. The InVO 4 in the composite illustrated a hollowed-out fibrous morphology and orthorhombic phase, and RGO nanosheets were nested in the InVO 4 nanofibers. The hybrid RGO could produce more hydroxyl groups and a higher oxygen vacancy density on the surface of RGO/InVO 4 composite. Compared with pure InVO 4 , the light absorption range of the as-prepared RGO/InVO 4 composite was expanded. In Rh B degradation, the RGO/InVO 4 hybrid nanofibers displayed a higher photocatalytic activity than pure InVO 4 nanofibers. The enhanced photocatalytic activity might be ascribed to the role of RGO as an electron transporter and acceptor in the composite, which could effectively inhibit the charge recombination and facilitate the charge transfer. The exported electron could attack an O 2 molecule to facilitate the generation of • O 2 − and • OH for the photodegradation process of Rh B.

  19. Roles of grain boundary and oxygen vacancies in Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} films for resistive switching device application

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xiaobing, E-mail: xiaobing-yan@126.com, E-mail: mseyanx@nus.edu.sg [Key Laboratory of Digital Medical Engineering of Hebei Province, College of Electron and Information Engineering, Hebei University, Baoding 071002 (China); Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore 117576 (Singapore); Li, Yucheng; Zhao, Jianhui; Li, Yan [Key Laboratory of Digital Medical Engineering of Hebei Province, College of Electron and Information Engineering, Hebei University, Baoding 071002 (China); Bai, Gang [College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Zhu, Siqi [Key Laboratory of Optoelectronic Information and Sensing Technologies of Guangdong Higher Education Institutes, Jinan University, Guangzhou 510632 (China)

    2016-01-18

    Oxygen vacancies are widely thought to be responsible for resistive switching (RS) effects based on polycrystalline oxides films. It is also well known that grain boundaries (GB) serve as reservoirs for accumulating oxygen vacancies. Here, Ar gas was introduced to enlarge the size of GB and increase the quantity of oxygen vacancies when the Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} (BST) films were deposited by pulse laser deposition technique. The experimental results indicate that the RS properties of the device exhibits better in the Ar-introduced BST films than in the O{sub 2}-grown BST films. High resolution transmission electron microscopy images show that an amorphous region GB with large size appears between two lattice planes corresponding to oxygen vacancies defects in the Ar-introduced BST. Fourier-transform infrared reflectivity spectroscopy results also reveal highly accumulated oxygen vacancies in the Ar-introduced BST films. And we propose that the conduction transport of the cell was dominantly contributed from not ions migration of oxygen vacancies but the electrons in our case according to the value of activation energies of two kinds of films.

  20. Identification and quantification of oxygen vacancies in CeO{sub 2} nanocrystals and their role in formation of F-centers

    Energy Technology Data Exchange (ETDEWEB)

    Jaffari, G.Hassnain, E-mail: hassnain@qau.edu.pk [Department of Physics, Quaid-i-Azam University Islamabad (Pakistan); Imran, Ali [Department of Physics, Quaid-i-Azam University Islamabad (Pakistan); Bah, M. [Department of Materials Science and Engineering, University of Delaware, 19716, Newark, DE (United States); Ali, Awais; Bhatti, Arshad S. [Centre for Micro and Nano Devices, Department of Physics, COMSATS Institute of Information Technology, Park Road, Islamabad, 44000 (Pakistan); Qurashi, Umar Saeed [Department of Physics, Quaid-i-Azam University Islamabad (Pakistan); Ismat Shah, S. [Department of Materials Science and Engineering, University of Delaware, 19716, Newark, DE (United States); Department of Physics, University of Delaware, 19716, Newark, DE (United States)

    2017-02-28

    Highlights: • Detail crystal and electronic structural analysis was employed to quantify oxygen vacancies. • The Raman F{sub 2g} mode shifted towards lower wave number, exhibiting mode softening with broader and asymmetric peak. • Observation of absorption edge revealed presence of 4f band within the band gap. • PL emission studies revealed presence of F-centers with corresponding energy level located below 4f band. • Transitions associated by the F-center are mainly associated with 4f{sup 0} to 4f{sup 1}, F{sup ++} to 4f{sup 1} and 4f{sup 0} to F{sup +}. - Abstract: In this work we present synthesis and extensive characterization of Cerium oxide (CeO{sub 2}) nanocrystals. Comparison between the properties of as-prepared and air annealed nanoparticles has been carried out, with a goal to clearly identify the effect of oxygen vacancies on crystal, electronic and band structure. Detail crystal and electronic structural analysis was employed to quantify oxygen vacancies. Structural analysis confirmed that the formation of single phase cubic Fluorite structure for both as-prepared and annealed samples. Crystal and electronic structural studies confirmed that Ce ions exists in two oxidation states, Ce{sup +3} and Ce{sup +4}. Concentration of oxygen vacancies was larger in as-synthesis nanocrystal. A drastic decrease in oxygen vacancy concentration was observed for the sample annealed in air at 550 °C. For the as-prepared sample, the Raman allowed F{sub 2g} mode shifted towards lower wavenumber, exhibiting mode softening with broader and asymmetric peak. Observation of absorption edge revealed presence of 4f band within the band gap. Absorption with different band edge, confirmed different energy position of 4f level for the sample possessing oxygen vacancies. Blue shift of the band edge for as-prepared sample has been discussed in terms of increase in lattice parameter, formation of Ce{sup +3} ions, quantum confinement effect etc. Photoluminescence emission

  1. Bonding of gold nanoclusters to oxygen vacancies on rutile TiO2(110)

    DEFF Research Database (Denmark)

    Lopez, Nuria; schaub, R.; Thostrup, P.

    2003-01-01

    Through an interplay between scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we show that bridging oxygen vacancies are the active nucleation sites for Au clusters on the rutile TiO2(110) surface. We find that a direct correlation exists between a decrease in...

  2. Factors determining the oxygen consumption rate (VO2) on-kinetics in skeletal muscles.

    OpenAIRE

    Korzeniewski, Bernard; Zoladz, Jerzy A

    2004-01-01

    Using a computer model of oxidative phosphorylation developed previously [Korzeniewski and Mazat (1996) Biochem. J. 319, 143-148; Korzeniewski and Zoladz (2001) Biophys. Chem. 92, 17-34], we analyse the effect of several factors on the oxygen-uptake kinetics, especially on the oxygen consumption rate (VO2) and half-transition time t(1/2), at the onset of exercise in skeletal muscles. Computer simulations demonstrate that an increase in the total creatine pool [PCr+/-Cr] (where Cr stands for c...

  3. Enhanced oxygen vacancy diffusion in Ta2O5 resistive memory devices due to infinitely adaptive crystal structure

    Science.gov (United States)

    Jiang, Hao; Stewart, Derek A.

    2016-04-01

    Metal oxide resistive memory devices based on Ta2O5 have demonstrated high switching speed, long endurance, and low set voltage. However, the physical origin of this improved performance is still unclear. Ta2O5 is an important archetype of a class of materials that possess an adaptive crystal structure that can respond easily to the presence of defects. Using first principles nudged elastic band calculations, we show that this adaptive crystal structure leads to low energy barriers for in-plane diffusion of oxygen vacancies in λ phase Ta2O5. Identified diffusion paths are associated with collective motion of neighboring atoms. The overall vacancy diffusion is anisotropic with higher diffusion barriers found for oxygen vacancy movement between Ta-O planes. Coupled with the fact that oxygen vacancy formation energy in Ta2O5 is relatively small, our calculated low diffusion barriers can help explain the low set voltage in Ta2O5 based resistive memory devices. Our work shows that other oxides with adaptive crystal structures could serve as potential candidates for resistive random access memory devices. We also discuss some general characteristics for ideal resistive RAM oxides that could be used in future computational material searches.

  4. Defective TiO2 with oxygen vacancies: synthesis, properties and photocatalytic applications

    Science.gov (United States)

    Pan, Xiaoyang; Yang, Min-Quan; Fu, Xianzhi; Zhang, Nan; Xu, Yi-Jun

    2013-04-01

    Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addition, we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial minireview would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the

  5. Using Dopants to Tune Oxygen Vacancy Formation in Transition Metal Oxide Resistive Memory.

    Science.gov (United States)

    Jiang, Hao; Stewart, Derek A

    2017-05-17

    Introducing dopants is an important way to tailor and improve electronic properties of transition metal oxides used as high-k dielectric thin films and resistance switching layers in leading memory technologies, such as dynamic and resistive random access memory (ReRAM). Ta 2 O 5 has recently received increasing interest because Ta 2 O 5 -based ReRAM demonstrates high switching speed, long endurance, and low operating voltage. However, advances in optimizing device characteristics with dopants have been hindered by limited and contradictory experiments in this field. We report on a systematic study on how various metal dopants affect oxygen vacancy formation in crystalline and amorphous Ta 2 O 5 from first principles. We find that isoelectronic dopants and weak n-type dopants have little impact on neutral vacancy formation energy and that p-type dopants can lower the formation energy significantly by introducing holes into the system. In contrast, n-type dopants have a deleterious effect and actually increase the formation energy for charged oxygen vacancies. Given the similar doping trend reported for other binary transition metal oxides, this doping trend should be universally valid for typical binary transition metal oxides. Based on this guideline, we propose that p-type dopants (Al, Hf, Zr, and Ti) can lower the forming/set voltage and improve retention properties of Ta 2 O 5 ReRAM.

  6. Understanding the presence of vacancy clusters in ZnO from a kinetic perspective

    International Nuclear Information System (INIS)

    Bang, Junhyeok; Zhang, S. B.; Kim, Youg-Sung; Park, C. H.; Gao, F.

    2014-01-01

    Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (V Zn  − Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of V Zn compared to V O , more V Zn -abundant clusters are formed than V O -abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (V Zn  − Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to V O donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations.

  7. First-principles simulations of the leakage current in metal-oxide-semiconductor structures caused by oxygen vacancies in HfO2 high-K gate dielectric

    International Nuclear Information System (INIS)

    Mao, L.F.; Wang, Z.O.

    2008-01-01

    HfO 2 high-K gate dielectric has been used as a new gate dielectric in metal-oxide-semiconductor structures. First-principles simulations are used to study the effects of oxygen vacancies on the tunneling current through the oxide. A level which is nearly 1.25 eV from the bottom of the conduction band is introduced into the bandgap due to the oxygen vacancies. The tunneling current calculations show that the tunneling currents through the gate oxide with different defect density possess the typical characteristic of stress-induced leakage current. Further analysis shows that the location of oxygen vacancies will have a marked effect on the tunneling current. The largest increase in the tunneling current caused by oxygen vacancies comes about at the middle oxide field when defects are located at the middle of the oxide. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Study of the movement of oxygen vacancies in the orthorhombic phase of YBa2Cu3O7-x by positron Doppler broadening spectroscopy

    International Nuclear Information System (INIS)

    Hong Zhang; Xiao-Gan Wang; Yao-Xian Fu

    1988-01-01

    The positron annihilation Doppler spectroscopy is used to monitor the movement of oxygen vacancy of YBa 2 Cu 3 O 7-x and an activation energy of (0.80 ± 0.10) eV for migration of oxygen vacancy in orthorhombic phase is obtained. (author)

  9. Defect chemistry modelling of oxygen-stoichiometry, vacancy concentrations, and conductivity of (La1-xSrx)(y)MnO3 +/-delta

    DEFF Research Database (Denmark)

    Poulsen, F.W.

    2000-01-01

    model, based on delocalised electrons, electron holes and all B-ions being trivalent is given in Appendix A. The sequential mathematical method allows us to calculate the high temperature oxygen partial pressure dependent properties of (La1-xSrx)(y)MnO3+/-delta in a unified manner irrespective...... are calculated by the small polaron model containing only ionic species - the B-ion may be Mn-B' (Mn2+), Mn-B(x) (Mn3+), and Mn-B(Mn4+). The A/B-ratio = y greatly influences the oxygen stoichiometry, oxygen ion vacancy- and cation vacancy concentrations and the total conductivity. Calculations are given...

  10. Ab Initio Metadynamics Study of the VO2+/VO2+ Redox Reaction Mechanism at the Graphite Edge/Water Interface.

    Science.gov (United States)

    Jiang, Zhen; Klyukin, Konstantin; Alexandrov, Vitaly

    2018-06-08

    Redox flow batteries (RFBs) are promising electrochemical energy storage systems, for which development is impeded by a poor understanding of redox reactions occurring at electrode/electrolyte interfaces. Even for the conventional all-vanadium RFB chemistry employing V 2+ /V 3+ and VO 2 + /VO 2+ couples, there is still no consensus about the reaction mechanism, electrode active sites, and rate-determining step. Herein, we perform Car-Parrinello molecular dynamics-based metadynamics simulations to unravel the mechanism of the VO 2 + /VO 2+ redox reaction in water at the oxygen-functionalized graphite (112̅0) edge surface serving as a representative carbon-based electrode. Our results suggest that during the battery discharge aqueous VO 2 + /VO 2+ species adsorb at the surface C-O groups as inner-sphere complexes, exhibiting faster adsorption/desorption kinetics than V 2+ /V 3+ , at least at low vanadium concentrations considered in our study. We find that this is because (i) VO 2 + /VO 2+ conversion does not involve the slow transfer of an oxygen atom, (ii) protonation of VO 2 + is spontaneous and coupled to interfacial electron transfer in acidic conditions to enable VO 2+ formation, and (iii) V 3+ found to be strongly bound to oxygen groups of the graphite surface features unfavorable desorption kinetics. In contrast, the reverse process taking place upon charging is expected to be more sluggish for the VO 2 + /VO 2+ redox couple because of both unfavorable deprotonation of the VO 2+ water ligands and adsorption/desorption kinetics.

  11. RGO/InVO{sub 4} hollowed-out nanofibers: Electrospinning synthesis and its application in photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Dong [Key Lab of Marine Environment and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100 (China); College of Resource and Environment, Qingdao Agricultural University, Qingdao 266109 (China); Zhang, Yanxiang [College of Environmental Science and Engineering, Shandong University, Jinan 250100 (China); Gao, Mengchun, E-mail: mengchungao@outlook.com [Key Lab of Marine Environment and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100 (China); Xin, Yanjun; Wu, Juan [College of Resource and Environment, Qingdao Agricultural University, Qingdao 266109 (China); Bao, Nan [College of Environmental Science and Engineering, Shandong University, Jinan 250100 (China)

    2015-10-30

    Graphical abstract: - Highlights: • RGO/InVO{sub 4} hollow-out nanofibers were obtained by electrospinning method. • The properties of InVO{sub 4} hollow-out nanofibers were deeply influenced by RGO. • RGO could reduce recombination of e{sup −}–h{sup +} pairs to improve photocatalytic activity. • Photo-induced h{sup +} and e{sup −} are the two main reactive species for RhB degradation. - Abstract: A composite of reduced graphene oxide (RGO) and InVO{sub 4} nanofiber was successfully synthesized by an electrospinning technique. The as-collected fibers were calcined at 420 °C in air and then calcined at 550 °C in nitrogen gas to remove polyvinyl pyrrolidone (PVP), which could enable InVO{sub 4} to crystallize and protect the RGO from oxidation. The InVO{sub 4} in the composite illustrated a hollowed-out fibrous morphology and orthorhombic phase, and RGO nanosheets were nested in the InVO{sub 4} nanofibers. The hybrid RGO could produce more hydroxyl groups and a higher oxygen vacancy density on the surface of RGO/InVO{sub 4} composite. Compared with pure InVO{sub 4}, the light absorption range of the as-prepared RGO/InVO{sub 4} composite was expanded. In Rh B degradation, the RGO/InVO{sub 4} hybrid nanofibers displayed a higher photocatalytic activity than pure InVO{sub 4} nanofibers. The enhanced photocatalytic activity might be ascribed to the role of RGO as an electron transporter and acceptor in the composite, which could effectively inhibit the charge recombination and facilitate the charge transfer. The exported electron could attack an O{sub 2} molecule to facilitate the generation of • O{sub 2}{sup −} and • OH for the photodegradation process of Rh B.

  12. Oxygen vacancy and Moessbauer parameters of Fe doped tin oxides

    International Nuclear Information System (INIS)

    Nomura, K.; Mudarra Navarro, A.M.; Errico, L.; Rodriguez Torres, C.E.

    2013-01-01

    It is not clear what the local environment of Fe ions included in rutile structure is. In order to clarify this point, Moessbauer parameters of 57 Fe doped SnO 2 are compared with the results of ab initio calculation taking into account different configurations of iron and oxygen vacancy in the rutile structure of SnO 2 . Calculations were performed using the LAPW+lo method (Wien2k); RMT x Kmax = 7, A mesh of 50 k-points at IBZ, 2x2x2 super cell of SnO 2 . (J.P.N.)

  13. Understanding the presence of vacancy clusters in ZnO from a kinetic perspective

    Energy Technology Data Exchange (ETDEWEB)

    Bang, Junhyeok; Zhang, S. B., E-mail: zhangs9@rpi.edu, E-mail: kimyongsung@gmail.com [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Kim, Youg-Sung, E-mail: zhangs9@rpi.edu, E-mail: kimyongsung@gmail.com [Korea Research Institute of Standards and Science, Daejeon 305-340 (Korea, Republic of); Department of Nano Science, University of Science and Technology, Daejeon 305-350 (Korea, Republic of); Park, C. H. [Research Center for Dielectric and Advanced Matter Physics, Pusan National University, Busan 609-735 (Korea, Republic of); Gao, F. [Pacific Northwest National Laboratory, MS K8-93, P.O. Box 999, Richland, Washington 99352 (United States)

    2014-06-23

    Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (V{sub Zn} − Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of V{sub Zn} compared to V{sub O}, more V{sub Zn}-abundant clusters are formed than V{sub O}-abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (V{sub Zn} − Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to V{sub O} donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations.

  14. Understanding cation ordering and oxygen vacancy site preference in Ba3CaNb2O9 from first-principles

    Science.gov (United States)

    Ding, Hepeng; Virkar, Anil; Liu, Feng

    2014-03-01

    We investigate the physical mechanism underlying the formation of the B-site cation ordering and the oxygen vacancy site selection in Ba3CaNb2O9 using density functional theory calculations. We found that either cation site exchange or oxygen vacancy formation induces negligible lattice strain. This implies that the ionic radius plays an insignificant role in governing these two processes. Furthermore, the electrostatic interactions are found dominant in the ordering of mixed valence species on one or more sites, the ionic bond strength is identified as the dominant force in governing both the 1:2 B-site cation ordering along the direction and the oxygen vacancy site preference in Ba3CaNb2O9. Specifically, the cation ordering can be rationalized by the increased mixing bonding energy of the Ca-O-Nb bonds over the Ca-O-Ca and Nb-O-Nb bonds, i.e., 1/2(Ca-O-Ca + Nb-O-Nb) Grant Number DE-SC0001061 as a flow through from the University of South Carolina.

  15. Improving the electrocatalytic performance of carbon nanotubes for VO"2"+/VO_2"+ redox reaction by KOH activation

    International Nuclear Information System (INIS)

    Dai, Lei; Jiang, Yingqiao; Meng, Wei; Zhou, Huizhu; Wang, Ling; He, Zhangxing

    2017-01-01

    Highlights: • KOH-activated carbon nanotubes (CNTs) was investigated as superior catalyst for VO"2"+/VO_2"+ redox reaction for vanadium redox flow battery (VRFB) for the first time. • KOH activation for CNTs can result in the chemical etching of surface and improved wettability, accelerating the mass transfer of vanadium ions. • KOH activation can introduce many oxygen-containing groups as active sites on the surface of CNTs. • KOH-activated CNTs as positive catalyst could increase the comprehensive energy storage performance of VRFB. - Abstract: In this paper, carbon nanotubes (CNTs) was activated by KOH treatment at high temperature and investigated as catalyst for VO"2"+/VO_2"+ redox reaction for vanadium redox flow battery (VRFB). X-ray photoelectron spectroscopy results suggest that the oxygen-containing groups can be introduced on CNTs by KOH activation. The mass transfer of vanadium ions can be accelerated by chemical etching by KOH activation and improved wettability due to the introduction of hydrophilic groups. The electrochemical properties of VO"2"+/VO_2"+ redox reaction can be enhanced by introduced oxygen-containing groups as active sites. The sample treated at 900 °C with KOH/CNTs mass ratio of 3:1 (CNTs-3) exhibits the highest electrocatalytic activity for VO"2"+/VO_2"+ redox reaction. The cell using CNTs-3 as positive catalyst demonstrates the smallest electrochemical polarization, the highest capacity and efficiency among the samples. Using KOH-activated CNTs-3 can increase the average energy efficiency of the cell by 4.4%. This work suggests that KOH-activated CNTs is a low-cost, efficient and promising catalyst for VO"2"+/VO_2"+ redox reaction for VRFB system.

  16. Oxygen microclusters in Czochralski-grown Si probed by positron annihilation

    International Nuclear Information System (INIS)

    Uedono, Akira; Wei Long; Tanigawa, Shoichiro; Kawano, Takao; Ikari, Atsushi; Kawakami, Kazuto; Itoh, Hisayoshi.

    1994-01-01

    Trapping of positrons by oxygen microclusters in Czochralski-grown Si was studied. Lifetime spectra of positrons were measured for Si specimens annealed in the temperature range between 450degC and 1000degC. Positrons were found to be trapped by oxygen microclusters, and the trapping rate of positrons into such defects increased with increasing annealing temperature. In order to investigate the clustering behaviors of oxygen atoms in more derail, vacancy-oxygen complexes, V n O m (n,m=1,2, ···), were introduced by 3MeV electron irradiation. The concentration of monovacancy-oxygen complexes VO m (m=2,3, ···) increased with increasing annealing temperature. These facts were attributed that the oxygen microclusters, O m , were introduced by annealing above 700degC. (author)

  17. Oxygen vacancy induced magnetization switching in Fe{sub 3}O{sub 4} epitaxial ultrathin films on GaAs(100)

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Zhaocong, E-mail: zhaocong.huang@gmail.com [Department of Physics, Southeast University, Nanjing 211189 (China); Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD (United Kingdom); School of Electronic Science and Engineering, Southeast University, Nanjing 210096 (China); Chen, Qian; Zhai, Ya, E-mail: yazhai@seu.edu.cn, E-mail: jlwang@seu.edu.cn; Wang, Jinlan, E-mail: yazhai@seu.edu.cn, E-mail: jlwang@seu.edu.cn [Department of Physics, Southeast University, Nanjing 211189 (China); Xu, Yongbing [Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD (United Kingdom); Wang, Baoping [School of Electronic Science and Engineering, Southeast University, Nanjing 210096 (China)

    2015-05-04

    The magnetic and transport properties of half metallic Fe{sub 3}O{sub 4}, which are sensitive to the stoichiometry, are the key issue for applications in spintronics. An anomalous enlargement of the saturation magnetic moment is found in a relatively thick sample of epitaxial Fe{sub 3}O{sub 4} film by post-growth oxidation method. The investigation of the thickness dependence of magnetic moment suggests that the enhanced magnetism moment may come from the existence of oxygen vacancies. First-principles calculations reveal that with oxygen vacancies in Fe{sub 3}O{sub 4} crystal the spin of Fe ions in the tetrahedron site near the vacancy is much easier to switch parallel to the Fe ions in the octahedron site by temperature disturbance, supported by the temperature dependence of magnetic moment of Fe{sub 3}O{sub 4} films in experiment.

  18. Oxygen Vacancies versus Fluorine at CeO 2 (111) : A Case of Mistaken Identity?

    NARCIS (Netherlands)

    Kullgren, J.; Wolf, M.J.; Castleton, C.W.M.; Mitev, P.; Briels, Willem J.; Hermansson, K.

    2014-01-01

    We propose a resolution to the puzzle presented by the surface defects observed with STM at the (111) surface facet of CeO 2 single crystals. In the seminal paper of Esch et al. [Science 309, 752 (2005)] they were identified with oxygen vacancies, but the observed behavior of these defects is

  19. Oxygen vacancies induced enhancement of photoconductivity of La0.5Sr0.5CoO3 - δ thin film

    Science.gov (United States)

    Gao, R. L.; Fu, C. L.; Cai, W.; Chen, G.; Deng, X. L.; Yang, H. W.; Sun, J. R.; Zhao, Y. G.; Shen, B. G.

    2014-09-01

    Effects of light and electrical current on the electrical transport properties and photovoltaic properties of oxygen-stoichiometric La0.5Sr0.5CoO3 and oxygen-deficient La0.5Sr0.5CoO3 - δ films prepared by pulsed laser deposition have been investigated. Oxygen-deficient films annealed in a vacuum show an obvious increase of resistance and lattice parameter. Besides, a direct correlation between the magnitude of the photoconductivity and oxygen vacancies in La0.5Sr0.5CoO3 - δ films has been observed. The light illumination causes a resistance drop to show the photoconductivity effect. Moreover, the photoconductivity can be remarkably enhanced by increasing the electrical current, that is, it exhibits current-enhanced photoconductivity (CEPC) effect. Oxygen deficiency in the annealed film leads to the formation of a structural disorder in the Co-O-Co conduction channel due to the accumulated oxygen vacancies and hence is believed to be responsible for the increase in higher photoconductivity. These results may be important for practical applications in photoelectric devices.

  20. Oxygen vacancy tuned Ohmic-Schottky conversion for enhanced performance in β-Ga{sub 2}O{sub 3} solar-blind ultraviolet photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Guo, D. Y.; Wu, Z. P.; An, Y. H.; Guo, X. C.; Chu, X. L.; Sun, C. L.; Tang, W. H., E-mail: whtang@bupt.edu.cn [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Li, L. H. [Physics Department, The State University of New York at Potsdam, Potsdam, New York 13676-2294 (United States); Li, P. G., E-mail: pgli@zstu.edu.cn [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Center for Optoelectronics Materials and Devices, Department of Physics, Zhejiang Sci-Tech University, Hangzhou, 310018 Zhejiang (China)

    2014-07-14

    β-Ga{sub 2}O{sub 3} epitaxial thin films were deposited using laser molecular beam epitaxy technique and oxygen atmosphere in situ annealed in order to reduce the oxygen vacancy. Metal/semiconductor/metal structured photodetectors were fabricated using as-grown film and annealed film separately. Au/Ti electrodes were Ohmic contact with the as-grown films and Schottky contact with the annealed films. In compare with the Ohmic-type photodetector, the Schottky-type photodetector takes on lower dark current, higher photoresponse, and shorter switching time, which benefit from Schottky barrier controlling electron transport and the quantity of photogenerated carriers trapped by oxygen vacancy significant decreasing.

  1. Oxygen vacancy induced by La and Fe into ZnO nanoparticles to modify ferromagnetic ordering

    International Nuclear Information System (INIS)

    Verma, Kuldeep Chand; Kotnala, R.K.

    2016-01-01

    We reported long-range ferromagnetic interactions in La doped Zn 0.95 Fe 0.05 O nanoparticles that mediated through lattice defects or vacancies. Zn 0.92 Fe 0.05 La 0.03 O (ZFLaO53) nanoparticles were synthesized by a sol–gel process. X-ray fluorescence spectrum of ZFLaO53 detects the weight percentage of Zn, Fe, La and O. X-ray diffraction shows the hexagonal Wurtzite ZnO phase. The Rietveld refinement has been used to calculate the lattice parameters and the position of Zn, Fe, La and O atoms in the Wurtzite unit cell. The average size of ZFLaO53 nanoparticles is 99 nm. The agglomeration type product due to OH ions with La results into ZnO nanoparticles than nanorods that found in pure ZnO and Zn 0.95 Fe 0.05 O sample. The effect of doping concentration to induce Wurtzite ZnO structure and lattice defects has been analyzed by Raman active vibrational modes. Photoluminescence spectra show an abnormal emission in both UV and visible region, and a blue shift at near band edge is formed with doping. The room temperature magnetic measurement result into weak ferromagnetism but pure ZnO is diamagnetic. However, the temperature dependent magnetic measurement using zero-field and field cooling at dc magnetizing field 500 Oe induces long-range ferromagnetic ordering. It results into antiferromagnetic Neel temperature of ZFLaO53 at around 42 K. The magnetic hysteresis is also measured at 200, 100, 50 and 10 K measurement that indicate enhancement in ferromagnetism at low temperature. Overall, the La doping into Zn 0.95 Fe 0.05 O results into enhanced antiferromagnetic interaction as well as lattice defects/vacancies. The role of the oxygen vacancy as the dominant defects in doped ZnO must form Bound magnetic polarons has been described. - Graphical abstract: The long-range ferromagnetic order in Zn 0.92 Fe 0.05 La 0.03 O nanoparticles at low temperature measurements involves oxygen vacancy as the medium of magnetic interactions. - Highlights: • The La and Fe doping

  2. Correlating oxygen vacancies and phase ratio/interface with efficient photocatalytic activity in mixed phase TiO2

    International Nuclear Information System (INIS)

    Verma, Ranjana; Samdarshi, S.K.

    2015-01-01

    Graphical abstract: The correlation of interfacial behavior and oxygen vacancies in mixed phase titania nanoparticles on their performance as photocatalyst has been investigated to explain the impact of photoactivity under UV and visible irradiation compared to pristine counterparts. The defects at the junction effectively reduce the band gap as well decrease the carrier recombination to enhance the photocatalytic activity. - Highlights: • Pristine and mixed phases (A/R ratio) TiO 2 synthesized by sol gel route. • Photoactivity variation has been correlated with the changes in the phase ratio. • Enhanced UV and visible activity attributable to oxygen vacancy present at the interface. • Role of A/R ratio and oxygen vacancy in the photoactivity of mixed TiO 2 depicted through a model. - Abstract: The photocatalytic activity is a result of the synergy of a succession of phenomena-photogeneration, separation, and participation of the charge carriers in redox reaction at the catalyst surface. While the extent of photogeneration is assessable in terms of absorption spectrum (band gap), the redox reaction can be correlated to specific surface area. However the respective change in the photocatalytic activity has not been rationally and consistently correlated with the above mentioned parameters. A satisfactory explanation of suppression of recombination based on separation of carriers due to differential mobility/diffusivity in the material phase(s) and/or intrinsic potential barrier exists but its correlation with common identifiable parameter/characteristics is still elusive. This paper attempts to address this issue by correlating the carrier separation with the phase ratio (phase interface) in mixed phase titania and generalizing it with the presence of oxygen vacancy at the phase interface. It essentially appears to complete the quest for identifiable parameters in the sequence of phenomena, which endow a photocatalyst with an efficient activity level. It has

  3. Simple method to enhance positive bias stress stability of In-Ga-Zn-O thin-film transistors using a vertically graded oxygen-vacancy active layer.

    Science.gov (United States)

    Park, Ji Hoon; Kim, Yeong-Gyu; Yoon, Seokhyun; Hong, Seonghwan; Kim, Hyun Jae

    2014-12-10

    We proposed a simple method to deposit a vertically graded oxygen-vacancy active layer (VGA) to enhance the positive bias stress (PBS) stability of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). We deposited a-IGZO films by sputtering (target composition; In2O3:Ga2O3:ZnO = 1:1:1 mol %), and the oxygen partial pressure was varied during deposition so that the front channel of the TFTs was fabricated with low oxygen partial pressure and the back channel with high oxygen partial pressure. Using this method, we were able to control the oxygen vacancy concentration of the active layer so that it varied with depth. As a result, the turn-on voltage shift following a 10 000 s PBS of optimized VGA TFT was drastically improved from 12.0 to 5.6 V compared with a conventional a-IGZO TFT, without a significant decrease in the field effect mobility. These results came from the self-passivation effect and decrease in oxygen-vacancy-related trap sites of the VGA TFTs.

  4. Periodic density functional theory study of ethylene hydrogenation over Co3O4 (1 1 1) surface: The critical role of oxygen vacancies

    International Nuclear Information System (INIS)

    Lu, Jinhui; Song, JiaJia; Niu, Hongling; Pan, Lun; Zhang, Xiangwen; Wang, Li; Zou, Ji-Jun

    2016-01-01

    Highlights: • H 2 dissociates in heterolytic way following H atoms migration to form O−H bond. • H 2 dissociation occurs at low temperature on perfect and oxygen defective Co 3 O 4 . • Oxygen vacancy promotes hydrogenation thermodynamically and kinetically. • O−H bond is weakened on oxygen defective surface. • Hydrogenation requires compromise between H−H activation and O−H breakage. - Abstract: Recently, metal oxides are attracting increasing interests as hydrogenation catalyst. Herein we studied the hydrogenation of ethylene on perfect and oxygen defective Co 3 O 4 (1 1 1) using periodic density functional theory. The energetics and pathways of ethylene hydrogenation to ethane were determined. We have demonstrated that (i) H 2 dissociation on Co 3 O 4 is a complicated two-step process through a heterolytic cleavage, followed by the migration of H atom and finally yields the homolytic product on both perfect and oxygen defective Co 3 O 4 (1 1 1) surfaces easily. (ii) After introducing the surface oxygen vacancy, the stepwise hydrogenation of ethylene by atomic hydrogen is much easier than that on perfect surface due to the weaker bond strength of OH group. The strength of O−H bond is a crucial factor for the hydrogenation reaction which involves the breakage of O−H bond. The formation of oxygen vacancy increases the electronic charges at the adjacent surface O, which reduces its capability of further gaining electrons from adsorbed atomic hydrogen and then weakens the strength of O−H bond. These results emphasize the importance of the oxygen vacancies for hydrogenation on metal oxides.

  5. Oxygen microclusters in Czochralski-grown Si probed by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Wei Long; Tanigawa, Shoichiro [Tsukuba Univ., Ibaraki (Japan). Inst. of Materials Science; Kawano, Takao; Ikari, Atsushi; Kawakami, Kazuto; Itoh, Hisayoshi

    1994-08-01

    Trapping of positrons by oxygen microclusters in Czochralski-grown Si was studied. Lifetime spectra of positrons were measured for Si specimens annealed in the temperature range between 450degC and 1000degC. Positrons were found to be trapped by oxygen microclusters, and the trapping rate of positrons into such defects increased with increasing annealing temperature. In order to investigate the clustering behaviors of oxygen atoms in more derail, vacancy-oxygen complexes, V{sub n}O{sub m} (n,m=1,2, {center_dot}{center_dot}{center_dot}), were introduced by 3MeV electron irradiation. The concentration of monovacancy-oxygen complexes VO{sub m}(m=2,3, {center_dot}{center_dot}{center_dot}) increased with increasing annealing temperature. These facts were attributed that the oxygen microclusters, O{sub m}, were introduced by annealing above 700degC. (author).

  6. A Facile Approach to Prepare Black TiO2 with Oxygen Vacancy for Enhancing Photocatalytic Activity

    Science.gov (United States)

    Chen, Shihao; Xiao, Yang; Hu, Zhengfa; Zhao, Hui; Xie, Wei

    2018-01-01

    Black TiO2 has triggered worldwide research interest due to its excellent photocatalytic properties. However, the understanding of its structure–property relationships and a more effective, facile and versatile method to produce it remain great challenges. We have developed a facile approach to synthesize black TiO2 nanoparticles with significantly improved light absorption in the visible and infrared regions. The experimental results show that oxygen vacancies are the major factors responsible for black coloration. More importantly, our black TiO2 nanoparticles have no Ti3+ ions. These oxygen vacancies could introduce localized states in the bandgap and act as trap centers, significantly decreasing the electron–hole recombination. The photocatalytic decomposition of both rhodamine B and methylene blue demonstrated that, under ultraviolet light irradiation, better photocatalytic performance is achieved with our black TiO2 nanoparticles than with commercial TiO2 nanoparticles. PMID:29659500

  7. Sn doped TiO{sub 2} nanotube with oxygen vacancy for highly efficient visible light photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jinliang; Xu, Xingtao [Engineering Research Center for Nanophotonics & Advanced Instrument, Ministry of Education, Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, Department of Physics, East China Normal University, Shanghai 200062 (China); Liu, Xinjuan [Institute of Coordination Bond Metrology and Engineering, College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018 (China); Yu, Caiyan; Yan, Dong; Sun, Zhuo [Engineering Research Center for Nanophotonics & Advanced Instrument, Ministry of Education, Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, Department of Physics, East China Normal University, Shanghai 200062 (China); Pan, Likun, E-mail: lkpan@phy.ecnu.edu.cn [Engineering Research Center for Nanophotonics & Advanced Instrument, Ministry of Education, Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, Department of Physics, East China Normal University, Shanghai 200062 (China)

    2016-09-15

    Sn doped TiO{sub 2} nanotube with oxygen vacancy (V{sub o}-Sn−TiO{sub 2}) was successfully synthesized via a facile hydrothermal process and subsequent annealing in nitrogen atmosphere. The morphology, structure and photocatalytic performance of V{sub o}-Sn−TiO{sub 2} in the degradation of nitrobenzene were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV–vis absorption spectroscopy, nitrogen adsorption-desorption and electrochemical impedance spectra, respectively. The inner diameter, outer diameter and specific surface area of V{sub o}-Sn−TiO{sub 2} are about 5 nm, 15 nm and 235.54 m{sup 2} g{sup −1}, respectively. The experimental results show that the V{sub o}-Sn−TiO{sub 2} exhibits excellent photocatalytic performance with a maximum degradation rate of 92% in 300 min for nitrobenzene and 94% in 100 min for Rhodamine B and corresponding mineralization rates of 68% and 70% under visible light irradiation. The improved photocatalytic performance is ascribed to the enhanced light absorption and specific surface area as well as the reduced electron-hole pair recombination with the presence of oxygen vacancy and Sn doping in the TiO{sub 2} nanotube. - Highlights: • Photocatalysis is an environmental-friendly technology for nitrobenzene removal. • Sn doped TiO{sub 2} nanotube with oxygen vacancy is fabricated for the first time. • It exhibits excellent photocatalytic performance in degradation of nitrobenzene. • A high degradation rate of 92% is achieved under visible light irradiation.

  8. Periodic density functional theory study of ethylene hydrogenation over Co3O4 (1 1 1) surface: The critical role of oxygen vacancies

    Science.gov (United States)

    Lu, Jinhui; Song, JiaJia; Niu, Hongling; Pan, Lun; Zhang, Xiangwen; Wang, Li; Zou, Ji-Jun

    2016-05-01

    Recently, metal oxides are attracting increasing interests as hydrogenation catalyst. Herein we studied the hydrogenation of ethylene on perfect and oxygen defective Co3O4 (1 1 1) using periodic density functional theory. The energetics and pathways of ethylene hydrogenation to ethane were determined. We have demonstrated that (i) H2 dissociation on Co3O4 is a complicated two-step process through a heterolytic cleavage, followed by the migration of H atom and finally yields the homolytic product on both perfect and oxygen defective Co3O4 (1 1 1) surfaces easily. (ii) After introducing the surface oxygen vacancy, the stepwise hydrogenation of ethylene by atomic hydrogen is much easier than that on perfect surface due to the weaker bond strength of OH group. The strength of Osbnd H bond is a crucial factor for the hydrogenation reaction which involves the breakage of Osbnd H bond. The formation of oxygen vacancy increases the electronic charges at the adjacent surface O, which reduces its capability of further gaining electrons from adsorbed atomic hydrogen and then weakens the strength of Osbnd H bond. These results emphasize the importance of the oxygen vacancies for hydrogenation on metal oxides.

  9. Effect of tin doping on oxygen- and carbon-related defects in Czochralski silicon

    International Nuclear Information System (INIS)

    Chroneos, A.; Londos, C. A.; Sgourou, E. N.

    2011-01-01

    Experimental and theoretical techniques are used to investigate the impact of tin doping on the formation and the thermal stability of oxygen- and carbon-related defects in electron-irradiated Czochralski silicon. The results verify previous reports that Sn doping reduces the formation of the VO defect and suppresses its conversion to the VO 2 defect. Within experimental accuracy, a small delay in the growth of the VO 2 defect is observed. Regarding carbon-related defects, it is determined that Sn doping leads to a reduction in the formation of the C i O i , C i C s , and C i O i (Si I ) defects although an increase in their thermal stability is observed. The impact of strain induced in the lattice by the larger tin substitutional atoms, as well as their association with intrinsic defects and carbon impurities, can be considered as an explanation to account for the above observations. The density functional theory calculations are used to study the interaction of tin with lattice vacancies and oxygen- and carbon-related clusters. Both experimental and theoretical results demonstrate that tin co-doping is an efficient defect engineering strategy to suppress detrimental effects because of the presence of oxygen- and carbon-related defect clusters in devices.

  10. Hydroxyl-dependent Evolution of Oxygen Vacancies Enables the Regeneration of BiOCl photocatalyst

    KAUST Repository

    Wu, Sujuan

    2017-05-02

    Photoinduced oxygen vacancies (OVs) are widely investigated as a vital point defect in wide-band-gap semiconductors. Still, the formation mechanism of OVs remains unclear in various materials. To elucidate the formation mechanism of photoinduced OVs in bismuth oxychloride (BiOCl), we synthesized two surface hydroxyl discrete samples in light of the discovery of the significant variance of hydroxyl groups before and after UV light exposure. It is noted that OVs can be obtained easily after UV light irradiation in the sample with surface hydroxyl groups, while variable changes were observed in samples without surface hydroxyls. Density functional theory (DFT) calculations reveal that the binding energy of Bi-O is drastically influenced by surficial hydroxyl groups, which is intensely correlated to the formation of photoinduced OVs. Moreover, DFT calculations reveal that the adsorbed water molecules are energetically favored to dissociate into separate hydroxyl groups at the OV sites via proton transfer to a neighboring bridging oxygen atom, forming two bridging hydroxyl groups per initial oxygen vacancy. This result is consistent with the experimental observation that the disappearance of photoinduced OVs and the recovery of hydroxyl groups on the surface of BiOCl after exposed to a H2O(g)-rich atmosphere, and finally enables the regeneration of BiOCl photocatalyst. Here, we introduce new insights that the evolution of photoinduced OVs is dependent on surface hydroxyl groups, which will lead to the regeneration of active sites in semiconductors. This work is useful for controllable designs of defective semiconductors for applications in photocatalysis and photovoltaics.

  11. Unraveling the facet-dependent and oxygen vacancy role for ethylene hydrogenation on Co_3O_4 (110) surface: A DFT+U study

    International Nuclear Information System (INIS)

    Zhang, Yong-Chao; Pan, Lun; Lu, Jinhui; Song, Jiajia; Li, Zheng; Zhang, Xiangwen; Wang, Li; Zou, Ji-Jun

    2017-01-01

    Highlights: • The mechanism of ethylene hydrogenation on perfect and oxygen defective Co_3O_4(110) is investigated by using DFT + U. • Oxygen vacancy promotes ethylene hydrogenation thermodynamically and kinetically. • The Co3O4 (110) facet is more active than the (111) one for ethylene hydrogenation. - Abstract: Crystal facet engineering and defect engineering are both critical strategies to improve the catalytic hydrogenation performance of catalyst. Herein, ethylene hydrogenation on the perfect and oxygen defective Co_3O_4(110) surfaces has been studied by using periodic density functional theory calculations. The results are compared with that on Co_3O_4(111) surface to clarify the problem of which facet for Co_3O_4 is more reactive, and to illuminate the role of oxygen vacancy. The low oxygen vacancy formation energy suggests that Co_3O_4(110) surface with defective site is easily formed. The whole mechanism of H_2 dissociation and stepwise hydrogenation of ethylene to ethane is examined, and the most favorable pathway is heterolytic dissociation of H_2 follows two stepwise hydrogenation of ethylene process. The results show that ethyl hydrogenation to ethane on perfect Co_3O_4(110) surface is the rate limiting step with an activation energy of 1.19 eV, and the presence of oxygen vacancy strongly reduces the activation energies of main elementary steps, and the activation energy of rate limiting step is only 0.47 eV. Compared with that on Co_3O_4(111), ethylene hydrogenation is preferred on Co_3O_4(110) surface. Therefore, Co_3O_4 with exposed (110) facet is predicted as an excellent catalyst for ethylene hydrogenation.

  12. Improving the electrocatalytic performance of carbon nanotubes for VO{sup 2+}/VO{sub 2}{sup +} redox reaction by KOH activation

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Lei; Jiang, Yingqiao; Meng, Wei; Zhou, Huizhu [School of Chemical Engineering, North China University of Science and Technology, Tangshan 063009 (China); Wang, Ling, E-mail: tswling@126.com [School of Chemical Engineering, North China University of Science and Technology, Tangshan 063009 (China); He, Zhangxing, E-mail: zxhe@ncst.edu.cn [School of Chemical Engineering, North China University of Science and Technology, Tangshan 063009 (China); State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, Nanchang 330013 (China)

    2017-04-15

    Highlights: • KOH-activated carbon nanotubes (CNTs) was investigated as superior catalyst for VO{sup 2+}/VO{sub 2}{sup +} redox reaction for vanadium redox flow battery (VRFB) for the first time. • KOH activation for CNTs can result in the chemical etching of surface and improved wettability, accelerating the mass transfer of vanadium ions. • KOH activation can introduce many oxygen-containing groups as active sites on the surface of CNTs. • KOH-activated CNTs as positive catalyst could increase the comprehensive energy storage performance of VRFB. - Abstract: In this paper, carbon nanotubes (CNTs) was activated by KOH treatment at high temperature and investigated as catalyst for VO{sup 2+}/VO{sub 2}{sup +} redox reaction for vanadium redox flow battery (VRFB). X-ray photoelectron spectroscopy results suggest that the oxygen-containing groups can be introduced on CNTs by KOH activation. The mass transfer of vanadium ions can be accelerated by chemical etching by KOH activation and improved wettability due to the introduction of hydrophilic groups. The electrochemical properties of VO{sup 2+}/VO{sub 2}{sup +} redox reaction can be enhanced by introduced oxygen-containing groups as active sites. The sample treated at 900 °C with KOH/CNTs mass ratio of 3:1 (CNTs-3) exhibits the highest electrocatalytic activity for VO{sup 2+}/VO{sub 2}{sup +} redox reaction. The cell using CNTs-3 as positive catalyst demonstrates the smallest electrochemical polarization, the highest capacity and efficiency among the samples. Using KOH-activated CNTs-3 can increase the average energy efficiency of the cell by 4.4%. This work suggests that KOH-activated CNTs is a low-cost, efficient and promising catalyst for VO{sup 2+}/VO{sub 2}{sup +} redox reaction for VRFB system.

  13. A quantum-chemical study of oxygen-vacancy defects in PbTiO3 crystals

    International Nuclear Information System (INIS)

    Stashans, Arvids; Serrano, Sheyla; Medina, Paul

    2006-01-01

    Investigation of an oxygen vacancy and F center in the cubic and tetragonal lattices of PbTiO 3 crystals is done by means of quantum-chemical simulations. Displacements of defect-surrounding atoms, electronic and optical properties, lattice relaxation energies and some new effects due to the defects presence are reported and analyzed. A comparison with similar studies is made and conclusions are drawn on the basis of the obtained results

  14. The modulation of oxygen vacancies by the combined current effect and temperature cycling in La0.7Sr0.3CoO3 film

    Science.gov (United States)

    Li, J.; Wang, J.; Kuang, H.; Zhao, Y. Y.; Qiao, K. M.; Liu, Y.; Hu, F. X.; Sun, J. R.; Shen, B. G.

    2018-05-01

    Modulating the oxygen defect concentration has been accepted as an effective method to obtain high catalytic activity in perovskite cobaltites. However, controllably modifying the oxygen vacancy is still a challenge in this type of materials, which strongly obstructs their application. Here, we report a successful oxygen vacancies modulation in the La0.7Sr0.3CoO3 (LSCO) film by using combined current effect and temperature cycling. The temperature dependent transport properties of the LSCO/LAO film were investigated. The results revealed that the resistance of the film keeps increasing under the repeated measurements. It was found that the accumulation of the oxygen vacancy by current effect transforms the Co4+ ion into Co3+ ion, which results in the enhancement of the resistance and thus the transport switching behavior. Moreover, the resistance in the cooling process was found to be much higher than that in previous cooling and heating processes, which indicates that the oxygen escapes more quickly in the high temperature region. On the other hand, our analysis indicates that the CoO6 distortion may contribute to the switching of transport behaviors in the low temperature region. Our work provides an effective and controllable way to modulate oxygen defect in the perovskite-type oxides.

  15. Microstructure and thermochromic properties of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films

    Energy Technology Data Exchange (ETDEWEB)

    Khamseh, S.; Ghahari, M. [Institute for Color Science and Technology, Department of Nanomaterial and Nanocoatings, Tehran (Iran, Islamic Republic of); Araghi, H. [Islamic Azad University, Department of Materials Engineering, Science and Research Branch, Tehran (Iran, Islamic Republic of); Faghihi Sani, M.A. [Sharif University of Technology, Department of Materials Science and Engineering, Tehran (Iran, Islamic Republic of)

    2016-03-15

    W-doped VO{sub 2} films have been synthesized via oxygen annealing of V-W-V (vanadium-tungsten-vanadium) multilayered films. The effects of middle layer's thickness of V-W-V multilayered film on structure and properties of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films were investigated. The as-deposited V-W-V multilayered film showed amorphous-like structure when mixed structure of VO{sub 2} (M) and VO{sub 2} (B) was formed in VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films. Tungsten content of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films increased with increasing middle layer's thickness. With increasing middle layer's thickness, room temperature square resistance (R{sub sq}) of VO{sub X}-WO{sub X}-VO{sub X} ceramic thin films increased from 65 to 86 kΩ/sq. The VO{sub X}-WO{sub X}-VO{sub X} ceramic thin film with the thinnest middle layer showed significant SMT (semiconductor-metal transition) when SMT became negligible on increasing middle layer's thickness. (orig.)

  16. Photocatalytic Conversion of Nitrogen to Ammonia with Water on Surface Oxygen Vacancies of Titanium Dioxide.

    Science.gov (United States)

    Hirakawa, Hiroaki; Hashimoto, Masaki; Shiraishi, Yasuhiro; Hirai, Takayuki

    2017-08-09

    Ammonia (NH 3 ) is an essential chemical in modern society. It is currently manufactured by the Haber-Bosch process using H 2 and N 2 under extremely high-pressure (>200 bar) and high-temperature (>673 K) conditions. Photocatalytic NH 3 production from water and N 2 at atmospheric pressure and room temperature is ideal. Several semiconductor photocatalysts have been proposed, but all suffer from low efficiency. Here we report that a commercially available TiO 2 with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N 2 , successfully produces NH 3 . The active sites for N 2 reduction are the Ti 3+ species on the oxygen vacancies. These species act as adsorption sites for N 2 and trapping sites for the photoformed conduction band electrons. These properties therefore promote efficient reduction of N 2 to NH 3 . The solar-to-chemical energy conversion efficiency is 0.02%, which is the highest efficiency among the early reported photocatalytic systems. This noble-metal-free TiO 2 system therefore shows a potential as a new artificial photosynthesis for green NH 3 production.

  17. The dynamics of ultraviolet-induced oxygen vacancy at the surface of insulating SrTiO_3(0 0 1)

    International Nuclear Information System (INIS)

    Suwanwong, S.; Eknapakul, T.; Rattanachai, Y.; Masingboon, C.; Rattanasuporn, S.; Phatthanakun, R.; Nakajima, H.; King, P.D.C.; Hodak, S.K.; Meevasana, W.

    2015-01-01

    Highlights: • The dynamics of UV-induced oxygen vacancy is studied from the change of surface resistance. • The formation of 2DEG at the insulating surface of SrTiO_3 is confirmed by ARPES. • The UV-induced change in resistance responds differently to oxygen/gas exposure. • The behavior of resistance recovery suggests an alternative method of low-pressure sensing. - Abstract: The effect of ultra-violet (UV) irradiation on the electronic structure and the surface resistance of an insulating SrTiO_3(0 0 1) crystal is studied in this work. Upon UV irradiation, we show that the two-dimensional electron gas (2DEG) emerges at the insulating SrTiO_3 surface and there is a pronounced change in the surface resistance. By combining the observations of the change in valance band and the resistance change under different environments of gas pressure and gas species, we find that UV-induced oxygen vacancies at the surface plays a major role in the resistance change. The dynamic of the resistance change at different oxygen pressures also suggests an alternative method of low-pressure sensing.

  18. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO{sub 3}-buffered ferroelectric BaTiO{sub 3} film on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Qiao, Qiao [Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607 (United States); Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37240 (United States); Materials Science and Technology Department, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Zhang, Yuyang [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37240 (United States); Materials Science and Technology Department, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Contreras-Guerrero, Rocio; Droopad, Ravi [Ingram School of Engineering, Texas State University, San Marcos, Texas 78666 (United States); Pantelides, Sokrates T. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37240 (United States); Materials Science and Technology Department, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37240 (United States); Pennycook, Stephen J. [Department of Materials Science and Engineering, National University of Singapore, Singapore 117575 (Singapore); Ogut, Serdar; Klie, Robert F. [Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607 (United States)

    2015-11-16

    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO{sub 3} thin films grown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO{sub 3} grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. Here, we use a combination of aberration-corrected scanning transmission electron microscopy and first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectric polarization of a BaTiO{sub 3} thin film grown on GaAs. We demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO{sub 3}), and propose that the presence of surface charge screening allows the formation of switchable domains.

  19. Oxygen vacancy effect on photoluminescence of KNb3O8 nanosheets

    Science.gov (United States)

    Li, Rui; Liu, Liying; Ming, Bangming; Ji, Yuhang; Wang, Ruzhi

    2018-05-01

    Fungus-like potassium niobate (KNb3O8) nanosheets have been synthesized on indium-doped tin oxide (ITO) glass substrates by a simple and environmental friendly two-step hydrothermal process. The prepared samples have been characterized by using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), High Resolution Transmission Electron Microscope (HRTEM), Fourier Transform Infra-Red Spectroscopy (FTIR), Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Furthermore, the photoluminescence (PL) of KNb3O8 nanosheets have been systematically studied. The results showed that the PL spectrum is between 300 and 645 nm with a 325 nm light excitation, which is divided into some sub-peaks. It is different from the perfect KNb3O8 nanosheets whose PL emission peaks located at near 433 nm. It should be originated from the effect of the oxygen (O) vacancies in the KNb3O8 nanosheets, which the PLs peaks can be found at about 490 nm and 530 nm by different position of O vacancy. The experimental results are in accordance with the first-principles calculations. Our results may present a feasible clue to estimate the defect position in KNb3O8 by the shape analysis of its spectrum of PLs.

  20. Simultaneous modulation of surface composition, oxygen vacancies and assembly in hierarchical Co3O4 mesoporous nanostructures for lithium storage and electrocatalytic oxygen evolution

    DEFF Research Database (Denmark)

    Sun, Hongyu; Zhao, Yanyan; Mølhave, Kristian

    2017-01-01

    in superior electrochemical properties when used as the anode materials for lithium-ion batteries and as an electrocatalyst for the oxygen evolution reaction. The excellent electrochemical performance is attributed to the synergistic effects of novel hierarchical morphology, crystal structure of the active...... materials, the improvement of intrinsic conductivity and inner surface area induced by the oxygen vacancies. The present strategy not only provides a facile method to assemble novel hierarchical architectures, but also paves a way to control surface structures (chemical composition and crystal defects...

  1. Unraveling the facet-dependent and oxygen vacancy role for ethylene hydrogenation on Co{sub 3}O{sub 4} (110) surface: A DFT+U study

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yong-Chao; Pan, Lun; Lu, Jinhui; Song, Jiajia; Li, Zheng; Zhang, Xiangwen; Wang, Li [Key Laboratory for Green Chemical Technology of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University (China); Collaborative Innovative Center of Chemical Science and Engineering (Tianjin), Tianjin 300072 (China); Zou, Ji-Jun, E-mail: jj_zou@tju.edu.cn [Key Laboratory for Green Chemical Technology of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University (China); Collaborative Innovative Center of Chemical Science and Engineering (Tianjin), Tianjin 300072 (China)

    2017-04-15

    Highlights: • The mechanism of ethylene hydrogenation on perfect and oxygen defective Co{sub 3}O{sub 4}(110) is investigated by using DFT + U. • Oxygen vacancy promotes ethylene hydrogenation thermodynamically and kinetically. • The Co3O4 (110) facet is more active than the (111) one for ethylene hydrogenation. - Abstract: Crystal facet engineering and defect engineering are both critical strategies to improve the catalytic hydrogenation performance of catalyst. Herein, ethylene hydrogenation on the perfect and oxygen defective Co{sub 3}O{sub 4}(110) surfaces has been studied by using periodic density functional theory calculations. The results are compared with that on Co{sub 3}O{sub 4}(111) surface to clarify the problem of which facet for Co{sub 3}O{sub 4} is more reactive, and to illuminate the role of oxygen vacancy. The low oxygen vacancy formation energy suggests that Co{sub 3}O{sub 4}(110) surface with defective site is easily formed. The whole mechanism of H{sub 2} dissociation and stepwise hydrogenation of ethylene to ethane is examined, and the most favorable pathway is heterolytic dissociation of H{sub 2} follows two stepwise hydrogenation of ethylene process. The results show that ethyl hydrogenation to ethane on perfect Co{sub 3}O{sub 4}(110) surface is the rate limiting step with an activation energy of 1.19 eV, and the presence of oxygen vacancy strongly reduces the activation energies of main elementary steps, and the activation energy of rate limiting step is only 0.47 eV. Compared with that on Co{sub 3}O{sub 4}(111), ethylene hydrogenation is preferred on Co{sub 3}O{sub 4}(110) surface. Therefore, Co{sub 3}O{sub 4} with exposed (110) facet is predicted as an excellent catalyst for ethylene hydrogenation.

  2. Porous VO(x)N(y) nanoribbons supported on CNTs as efficient and stable non-noble electrocatalysts for the oxygen reduction reaction.

    Science.gov (United States)

    Huang, K; Bi, K; Lu, Y K; Zhang, R; Liu, J; Wang, W J; Tang, H L; Wang, Y G; Lei, M

    2015-11-30

    Novel nanocomposites of carbon nanotubes supported porous VO(x)N(y) nonoribbons (VO(x)N(y)-CNTs) have been synthesized by the annealing of the sol-gel mixture of CNTs and V2O5 under NH3 atmosphere as well as the ageing process in air. Besides the morphological and structural characterizations revealed by TEM, SEAD, EDS, XRD and XPS measurements, typical electrochemical tests including cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry have been employed to determine the oxygen reduction reaction (ORR) performance of VO(x)N(y)-CNTs. Inspiringly, the results indicate that VO(x)N(y)-CNTs catalyst exhibits a 0.4 mA/cm(2) larger diffusion-limited current density, a 0.10  V smaller onset potential value, a 10.73% less of ORR current decay and an excellent methanol-tolerance compared with commercial Pt/C catalyst. Therefore, we have reasonable grounds to believe that this new VO(x)N(y)-CNTs nanocomposites can be regarded as a promising non-precious methanol-tolerant ORR catalyst candidate for alkaline fuel cells.

  3. Oxygen-Vacancy Abundant Ultrafine Co3O4/Graphene Composites for High-Rate Supercapacitor Electrodes.

    Science.gov (United States)

    Yang, Shuhua; Liu, Yuanyue; Hao, Yufeng; Yang, Xiaopeng; Goddard, William A; Zhang, Xiao Li; Cao, Bingqiang

    2018-04-01

    The metal oxides/graphene composites are one of the most promising supercapacitors (SCs) electrode materials. However, rational synthesis of such electrode materials with controllable conductivity and electrochemical activity is the topical challenge for high-performance SCs. Here, the Co 3 O 4 /graphene composite is taken as a typical example and develops a novel/universal one-step laser irradiation method that overcomes all these challenges and obtains the oxygen-vacancy abundant ultrafine Co 3 O 4 nanoparticles/graphene (UCNG) composites with high SCs performance. First-principles calculations show that the surface oxygen vacancies can facilitate the electrochemical charge transfer by creating midgap electronic states. The specific capacitance of the UCNG electrode reaches 978.1 F g -1 (135.8 mA h g -1 ) at the current densities of 1 A g -1 and retains a high capacitance retention of 916.5 F g -1 (127.3 mA h g -1 ) even at current density up to 10 A g -1 , showing remarkable rate capability (more than 93.7% capacitance retention). Additionally, 99.3% of the initial capacitance is maintained after consecutive 20 000 cycles, demonstrating enhanced cycling stability. Moreover, this proposed laser-assisted growth strategy is demonstrated to be universal for other metal oxide/graphene composites with tuned electrical conductivity and electrochemical activity.

  4. Efficient Visible Light Nitrogen Fixation with BiOBr Nanosheets of Oxygen Vacancies on the Exposed {001} Facets.

    Science.gov (United States)

    Li, Hao; Shang, Jian; Ai, Zhihui; Zhang, Lizhi

    2015-05-20

    Even though the well-established Haber-Bosch process has been the major artificial way to "fertilize" the earth, its energy-intensive nature has been motivating people to learn from nitrogenase, which can fix atmospheric N2 to NH3 in vivo under mild conditions with its precisely arranged proteins. Here we demonstrate that efficient fixation of N2 to NH3 can proceed under room temperature and atmospheric pressure in water using visible light illuminated BiOBr nanosheets of oxygen vacancies in the absence of any organic scavengers and precious-metal cocatalysts. The designed catalytic oxygen vacancies of BiOBr nanosheets on the exposed {001} facets, with the availability of localized electrons for π-back-donation, have the ability to activate the adsorbed N2, which can thus be efficiently reduced to NH3 by the interfacial electrons transferred from the excited BiOBr nanosheets. This study might open up a new vista to fix atmospheric N2 to NH3 through the less energy-demanding photochemical process.

  5. Decrease of oxygen vacancy by Zn-doped for improving solar-blind photoelectric performance in β-Ga2O3 thin films

    Science.gov (United States)

    Guo, Daoyou; Qin, Xinyuan; Lv, Ming; Shi, Haoze; Su, Yuanli; Yao, Guosheng; Wang, Shunli; Li, Chaorong; Li, Peigang; Tang, Weihua

    2017-11-01

    Highly (201) oriented Zn-doped β-Ga2O3 thin films with different dopant concentrations were grown on (0001) sapphire substrates by radio frequency magnetron sputtering. With the increase of Zn dopant concentration, the crystal lattice expands, the energy band gap shrinks, and the oxygen vacancy concentration decreases. Both the metal semiconductor metal (MSM) structure photodetectors based on the pure and Zn-doped β-Ga2O3 thin films exhibit solar blind UV photoelectric property. Compared to the pure β-Ga2O3 photodetector, the Zn-doped one exhibits a lower dark current, a higher photo/dark current ratio, a faster photoresponse speed, which can be attributed to the decreases of oxygen vacancy concentration.[Figure not available: see fulltext.

  6. The dynamics of ultraviolet-induced oxygen vacancy at the surface of insulating SrTiO{sub 3}(0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Suwanwong, S. [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Program in General Science Teaching, Faculty of Education, Vongchavalitkul University, Nakhon Ratchasima 30000 (Thailand); Eknapakul, T. [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Rattanachai, Y. [Department of Applied Physics, Faculty of Sciences and Liberal Arts, Rajamangala University of Technology Isan, Nakhon Ratchasima 30000 (Thailand); Masingboon, C. [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Faculty of Science and Engineering, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000 (Thailand); Rattanasuporn, S.; Phatthanakun, R.; Nakajima, H. [Synchrotron Light Research Institute, Nakhon Ratchasima 30000 (Thailand); King, P.D.C. [SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS (United Kingdom); Hodak, S.K. [Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330 (Thailand); Meevasana, W., E-mail: worawat@g.sut.ac.th [School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); NANOTEC-SUT Center of Excellence on Advanced Functional Nanomaterials, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand); Thailand Center of Excellence in Physics, CHE, Bangkok 10400 (Thailand)

    2015-11-15

    Highlights: • The dynamics of UV-induced oxygen vacancy is studied from the change of surface resistance. • The formation of 2DEG at the insulating surface of SrTiO{sub 3} is confirmed by ARPES. • The UV-induced change in resistance responds differently to oxygen/gas exposure. • The behavior of resistance recovery suggests an alternative method of low-pressure sensing. - Abstract: The effect of ultra-violet (UV) irradiation on the electronic structure and the surface resistance of an insulating SrTiO{sub 3}(0 0 1) crystal is studied in this work. Upon UV irradiation, we show that the two-dimensional electron gas (2DEG) emerges at the insulating SrTiO{sub 3} surface and there is a pronounced change in the surface resistance. By combining the observations of the change in valance band and the resistance change under different environments of gas pressure and gas species, we find that UV-induced oxygen vacancies at the surface plays a major role in the resistance change. The dynamic of the resistance change at different oxygen pressures also suggests an alternative method of low-pressure sensing.

  7. A quantum-chemical study of oxygen-vacancy defects in PbTiO{sub 3} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Stashans, Arvids [Laboratorio de Fisica, Escuela de Electronica y Telecomunicaciones, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)]. E-mail: arvids@utpl.edu.ec; Serrano, Sheyla [Centro de Investigacion en Fisica de Materia Condensada, Corporacion de Fisica Fundamental y Aplicada, Apartado 17-12-637, Quito (Ecuador); Escuela de Ingenierias, Universidad Politecnica Salesiana, Campus Sur, Rumichaca s/n y Moran Valverde, Apartado 17-12-536, Quito (Ecuador); Medina, Paul [Centro de Investigacion en Fisica de Materia Condensada, Corporacion de Fisica Fundamental y Aplicada, Apartado 17-12-637, Quito (Ecuador)

    2006-05-31

    Investigation of an oxygen vacancy and F center in the cubic and tetragonal lattices of PbTiO{sub 3} crystals is done by means of quantum-chemical simulations. Displacements of defect-surrounding atoms, electronic and optical properties, lattice relaxation energies and some new effects due to the defects presence are reported and analyzed. A comparison with similar studies is made and conclusions are drawn on the basis of the obtained results.

  8. Detection of oxygen vacancy defect states in capacitors with ultrathin Ta2O5 films by zero-bias thermally stimulated current spectroscopy

    International Nuclear Information System (INIS)

    Lau, W.S.; Leong, L.L.; Han, Taejoon; Sandler, Nathan P.

    2003-01-01

    Defect state D (0.8 eV) was experimentally detected in Ta 2 O 5 capacitors with ultrathin (physical thickness 2 O 5 films using zero-bias thermally stimulated current spectroscopy and correlated with leakage current. Defect state D can be more efficiently suppressed by using N 2 O rapid thermal annealing (RTA) instead of using O 2 RTA for postdeposition annealing and by using TiN instead of Al for top electrode. We believe that defect D is probably the first ionization level of the oxygen vacancy deep double donor. Other important defects are Si/O-vacancy complex single donors and C/O-vacancy complex single donors

  9. Extended x-ray absorption fine structure spectroscopy and x-ray absorption near edge spectroscopy study of aliovalent doped ceria to correlate local structural changes with oxygen vacancies clustering

    Energy Technology Data Exchange (ETDEWEB)

    Shirbhate, S. C.; Acharya, S. A., E-mail: saha275@yahoo.com [Department of Physics, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur 440033 (India); Yadav, A. K. [Atomic and molecular Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

    2016-04-04

    This study provides atomic scale insight to understand the role of aliovalent dopants on oxygen vacancies clustering and dissociation mechanism in ceria system in order to enhance the performance of oxy-ion conductor. Dopants induced microscale changes in ceria are probed by extended X-ray absorption fine structure spectroscopy, X-ray absorption near edge spectra, and Raman spectroscopy. The results are explored to establish a correlation between atomic level structural changes (coordination number, interatomic spacing) → formation of dimer and trimer type cation-oxygen vacancies defect complex (intrinsic and extrinsic) → dissociation of oxygen vacancies from defect cluster → ionic conductivity temperature. It is a strategic approach to understand key physics of ionic conductivity mechanism in order to reduce operating temperature of electrolytes for intermediate temperature (300–450 °C) electrochemical devices for the first time.

  10. Time limit and VO2 slow component at intensities corresponding to VO2max in swimmers.

    Science.gov (United States)

    Fernandes, R J; Cardoso, C S; Soares, S M; Ascensão, A; Colaço, P J; Vilas-Boas, J P

    2003-11-01

    The purpose of this study was to measure, in swimming pool conditions and with high level swimmers, the time to exhaustion at the minimum velocity that elicits maximal oxygen consumption (TLim at vVO(2)max), and the corresponding VO(2) slow component (O(2)SC). The vVO(2)max was determined through an intermittent incremental test (n = 15). Forty-eight hours later, TLim was assessed using an all-out swim at vVO(2)max until exhaustion. VO(2) was measured through direct oximetry and the swimming velocity was controlled using a visual light-pacer. Blood lactate concentrations and heart rate values were also measured. Mean VO(2)max for the incremental test was 5.09 +/- 0.53 l/min and the corresponding vVO(2)max was 1.46 +/- 0.06 m/s. Mean TLim value was 260.20 +/- 60.73 s and it was inversely correlated with the velocity of anaerobic threshold (r = -0.54, p energy cost of the respiratory muscles (r = 0.51), for p swimming pool, in high level swimmers performing at vVO(2)max, and that higher TLim seems to correspond to higher expected O(2)SC amplitude. These findings seem to bring new data with application in middle distance swimming.

  11. Clinical safety and parameters of maximum oxygen uptake (Vo/sub 2/ max) testing in pakistani patients with heart failure

    International Nuclear Information System (INIS)

    Hussain, S.; Kayani, A.M.

    2015-01-01

    To determine the parameters of maximum oxygen uptake (VO2 max) in a Pakistani systolic heart failure cohort and its safety in a clinical setting. Study Design: Descriptive study. Place and Duration of Study: Armed Forces Institute of Cardiology, National Institute of Heart Diseases, Rawalpindi, from June 2011 to January 2013. Methodology: Maximum oxygen uptake test was performed in patients with severe heart failure, who could perform the VO2 max treadmill test. Age, Body Mass Index (BMI) ejection fraction, VO2 max and respiratory exchange ratios and their correlations were determined. Results: Out of 135 patients, 77% (n=104) were males, with a mean age of 45.9 ± 15.7 years. Weight of patients ranged from 30 kg to 107 kg (mean 63.29 ± 13.6 kg); mean BMI was 23.16 ± 4.56 kg/m2. All patients presented with either NYHA class of III (50.3%; n=68) or IV (49.7%; n=67); mean ejection fraction was 22.54 ± 5.7% (10 - 35%, IQ:20 - 25). The VO2 max of the patients ranged from 3 to 32 ml/kg/minute (mean 12.85 ± 4.49 ml/kg/minute). Respiratory exchange ratio was over 1 for all patients (1.12 - 1.96, mean = 1.36 ± 0.187). There was a negative correlation with age (r = -0.204; p = 0.028) whereas a positive correlation was found with exercise time (r = 0.684; p = 0.000), hemoglobin (r = 0.190; p = 0.047) and ejection fraction (r = 0.187 ; p = 0.044). Conclusion: Cardiopulmonary exercise testing in a high-risk heart failure cohort is safe and provides information beyond the routine clinical evaluation of heart failure patients. (author)

  12. The role of Co impurities and oxygen vacancies in the ferromagnetism of Co-doped SnO2: GGA and GGA+U studies

    International Nuclear Information System (INIS)

    Wang Hongxia; Yan Yu; Mohammed, Y. Sh.; Du Xiaobo; Li Kai; Jin Hanmin

    2009-01-01

    The electronic structure and ferromagnetic stability of Co-doped SnO 2 are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+U schemes. The addition of effective U Co transforms the ground state of Co-doped SnO 2 to insulating from half-metallic and the coupling between the nearest neighbor Co spins to weak antimagnetic from strong ferromagnetic. GGA+U Co calculations show that the pure substitutional Co defects in SnO 2 cannot induce the ferromagnetism. Oxygen vacancies tend to locate near Co atoms. Their presence increases the magnetic moment of Co and induces the ferromagnetic coupling between two Co spins with large Co-Co distance. The calculated density of state and spin density distribution calculated by GGA+U Co show that the long-range ferromagnetic coupling between two Co spins is mediated by spin-split impurity band induced by oxygen vacancies. More charge transfer from impurity to Co-3d states and larger spin split of Co-3d and impurity states induced by the addition of U Co enhance the ferromagnetic stability of the system with oxygen vacancies. By applying a Coulomb U O on O 2 s orbital, the band gap is corrected for all calculations and the conclusions derived from GGA+U Co calculations are not changed by the correction of band gap.

  13. Migration mechanisms and diffusion barriers of vacancies in Ga2O3

    Science.gov (United States)

    Kyrtsos, Alexandros; Matsubara, Masahiko; Bellotti, Enrico

    2017-06-01

    We employ the nudged elastic band and the dimer methods within the standard density functional theory (DFT) formalism to study the migration of the oxygen and gallium vacancies in the monoclinic structure of β -Ga2O3 . We identify all the first nearest neighbor paths and calculate the migration barriers for the diffusion of the oxygen and gallium vacancies. We also identify the metastable sites of the gallium vacancies which are critical for the diffusion of the gallium atoms. The migration barriers for the diffusion of the gallium vacancies are lower than the migration barriers for oxygen vacancies by 1 eV on average, suggesting that the gallium vacancies are mobile at lower temperatures. Using the calculated migration barriers we estimate the annealing temperature of these defects within the harmonic transition state theory formalism, finding excellent agreement with the observed experimental annealing temperatures. Finally, we suggest the existence of percolation paths which enable the migration of the species without utilizing all the migration paths of the crystal.

  14. Study on the intrinsic defects in ZnO by combing first-principle and thermodynamic calculations

    Science.gov (United States)

    Ma, Changmin; Liu, Tingyu; Chang, Qiuxiang

    2015-11-01

    In this paper, the intrinsic point defects in ZnO crystal have been studied by the approach that integrates first-principles, thermodynamic calculations and the contributions of vibrational entropy. With temperature increasing and oxygen partial pressure decreasing, the formation energies of oxygen vacancy (VO), zinc interstitial (Zni) and zinc anti-site (ZnO) are decreasing, while it increases for zinc vacancy (VZn), oxygen interstitial (Oi) and oxygen anti-site (OZn). They are more sensitive to temperature than oxygen partial pressure. There are two interesting phenomena. First, VO or VZn have the lowest formation energies for whole Fermi level at special environment condition (such as at T = 300K, about PO2 = 10-10atm or T = 1500K, about PO2 = 104atm) and intrinsic p-type doping of ZnO is possible by VZn at these special conditions. Second, VO as donors have lowest formation energy for all Fermi level at high temperature and low oxygen partial pressure (T = 1500K, PO2 = 10-10atm). According to our analysis, the VO could produce n-type doping in ZnO at these special conditions and change p-type ZnO to n-type ZnO at condition from low temperature and high oxygen partial pressure to high temperature and low oxygen partial pressure.

  15. An Unusual Strong Visible-Light Absorption Band in Red Anatase TiO2 Photocatalyst Induced by Atomic Hydrogen-Occupied Oxygen Vacancies.

    Science.gov (United States)

    Yang, Yongqiang; Yin, Li-Chang; Gong, Yue; Niu, Ping; Wang, Jian-Qiang; Gu, Lin; Chen, Xingqiu; Liu, Gang; Wang, Lianzhou; Cheng, Hui-Ming

    2018-02-01

    Increasing visible light absorption of classic wide-bandgap photocatalysts like TiO 2 has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible-light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail-like absorption band in hydrogen-free oxygen-deficient TiO 2 , an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO 2 by intentionally introducing atomic hydrogen-mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo-electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide-bandgap semiconductors to fully capture solar light. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Experimental evidence for fast cluster formation of chain oxygen vacancies in YBa2Cu3O7-d being at the origin of the fishtail anomaly

    OpenAIRE

    Erb, Andreas; Manuel, Alfred A.; Dhalle, Marc; Marti, Frank; Genoud, Jean-Yves; Revaz, Bernard; Junod, Alain; Vasumathi, Dharmavaram; Ishibashi, Shoji; Shukla, Abhay; Walker, Eric; Fischer, Oystein; Fluekiger, Rene; Pozzi, Riccardo; Mali, Mihael

    1998-01-01

    We report on three different and complementary measurements, namely magnetisation measurements, positron annihilation spectroscopy and NMR measurements, which give evidence that the formation of oxygen vacancy clusters is on the origin of the fishtail anomaly in YBa2Cu3O7-d. While in the case of YBa2Cu3O7.0 the anomaly is intrinsically absent, it can be suppressed in the optimally doped state where vacancies are present. We therefore conclude that the single vacancies or point defects can not...

  17. Oxygen vacancy induced two-dimensional electron system in disordered-crystalline LaAlO{sub 3}/KTaO{sub 3} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zapf, Michael; Gabel, Judith; Scheiderer, Philipp; Dudy, Lenart; Sing, Michael; Claessen, Ralph [Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), Universitaet Wuerzburg (Germany); Schlueter, Christoph; Lee, Tien-Lin [Diamond Light Source Ltd., Didcot (United Kingdom)

    2016-07-01

    Two-dimensional electron systems (2DESs) in oxide heterostructures based on SrTiO{sub 3} are considered to be a promising platform for future microelectronic technology. A variety of interesting properties such as ferromagnetism, resistive switching and superconductivity are linked to interfacial n-doping involving oxygen vacancies. The introduction of a high Z-cation with large spin-orbit coupling like Ta offers an exciting new parameter. We report on a new oxygen vacancy induced 2DES located at the interface of disordered LaAlO{sub 3} and crystalline KTaO{sub 3}, which exhibits remarkably high electron mobilities and charge carrier concentrations. The number of charge carriers can be readily manipulated by the film thickness and irradiation with intense X-rays. Our synchrotron-based hard X-ray photoemission experiments provide a direct probe of the Ta 5d charge carriers at the buried interface to obtain information on the charge carrier density, its depth distribution, and the band structure.

  18. High-performance gas sensing achieved by mesoporous tungsten oxide mesocrystals with increased oxygen vacancies

    KAUST Repository

    Wang, Dong

    2013-01-01

    The inner structure of W18O49 mesocrystals was observed by electron microscopy with the help of ultramicrotomy and focused ion beam techniques. The results showed that these mesocrystals contain irregular mesopores formed through partial fusion of self-assembled nanowires, and consequently have long-range structural ordering in one dimension and short-range ordering in the other two dimensions. The W18O 49 mesocrystals exhibit superior performance in gas sensing applications, which is considered to be associated with the presence of more oxygen vacancy sites in the unique mesoporous structure. © 2013 The Royal Society of Chemistry.

  19. Surface oxygen vacancy and oxygen permeation flux limits of perovskite ion transport membranes

    KAUST Repository

    Hunt, Anton

    2015-09-01

    © 2015 Elsevier B.V. The mechanisms and quantitative models for how oxygen is separated from air using ion transport membranes (ITMs) are not well understood, largely due to the experimental complexity for determining surface exchange reactions at extreme temperatures (>800°C). This is especially true when fuels are present at the permeate surface. For both inert and reactive (fuels) operations, solid-state oxygen surface vacancies (δ) are ultimately responsible for driving the oxygen flux, JO2. In the inert case, the value of δ at either surface is a function of the local PO2 and temperature, whilst the magnitude of δ dictates both the JO2 and the inherent stability of the material. In this study values of δ are presented based on experimental measurements under inert (CO2) sweep: using a permeation flux model and local PO2 measurements, collected by means of a local gas-sampling probe in our large-scale reactor, we can determine δ directly. The ITM assessed was La0.9Ca0.1FeO3-δ (LCF); the relative resistances to JO2 were quantified using the pre-defined permeation flux model and local PO2 values. Across a temperature range from 825°C to 1056°C, δ was found to vary from 0.007 to 0.029 (<1%), safely within material stability limits, whilst the permeate surface exchange resistance dominates. An inert JO2 limit was identified owing to a maximum sweep surface δ, δmaxinert. The physical presence of δmaxinert is attributed to a rate limiting step shift from desorption to associative electron transfer steps on the sweep surface as PO2 is reduced. Permeate surface exchange limitations under non-reactive conditions suggest that reactive (fuel) operation is necessary to accelerate surface chemistry for future work, to reduce flux resistance and push δpast δmaxinert in a stable manner.

  20. Oxygen vacancy rich Cu2O based composite material with nitrogen doped carbon as matrix for photocatalytic H2 production and organic pollutant removal.

    Science.gov (United States)

    Lu, Lele; Xu, Xinxin; Yan, Jiaming; Shi, Fa-Nian; Huo, Yuqiu

    2018-02-06

    A nitrogen doped carbon matrix supported Cu 2 O composite material (Cu/Cu2O@NC) was fabricated successfully with a coordination polymer as precursor through calcination. In this composite material, Cu 2 O particles with a size of about 6-10 nm were dispersed evenly in the nitrogen doped carbon matrix. After calcination, some coordinated nitrogen atoms were doped in the lattice of Cu 2 O and replace oxygen atoms, thus generating a large number of oxygen vacancies. In Cu/Cu2O@NC, the existence of oxygen vacancies has been confirmed by electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS). Under visible light irradiation, Cu/Cu2O@NC exhibits excellent H 2 production with the rate of 379.6 μmol h -1 g -1 . Its photocatalytic activity affects organic dyes, such as Rhodamine B (RhB) and methyl orange (MO). In addition to photocatalysis, Cu/Cu2O@NC also exhibits striking catalytic activity in reductive conversion of 4-nitrophenol to 4-aminophenol with in presence of sodium borohydride (NaBH 4 ). The conversion efficiency reaches almost 100% in 250 s with the quantity of Cu/Cu2O@NC as low as 5 mg. The outstanding H 2 production and organic pollutants removal are attributed to the oxygen vacancy. We expect that Cu/Cu2O@NC will find its way as a new resource for hydrogen energy as well as a promising material in water purification.

  1. Oxygen vacancies at the spinel/perovskite γ-Al{sub 2}O{sub 3}/SrTiO{sub 3} heterointerface probed by resonant photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schuetz, Philipp; Pfaff, Florian; Zapf, Michael; Gabel, Judith; Dudy, Lenart; Berner, Goetz; Sing, Michael; Claessen, Ralph [Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), Universitaet Wuerzburg (Germany); Chen, Yunzhong; Pryds, Nini [Department of Energy Conversion and Storage, Technical University of Denmark, Risoe (Denmark); Schlueter, Christoph; Lee, Tien-Lin [Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot (United Kingdom)

    2016-07-01

    The spinel/perovskite heterointerface between the band insulators γ-Al{sub 2}O{sub 3} and SrTiO{sub 3} hosts a two-dimensional electron system (2DES) with exceptionally high electron mobility. Soft x-ray resonant photoelectron spectroscopy at the Ti L absorption edge is used to probe the Ti 3d derived interface states. Marked differences in the resonance behavior are found for the SrTiO{sub 3} valence band and the different interface states, which are observed in the band gap of SrTiO{sub 3}. A comparison to X-ray absorption spectra of Ti 3d{sup 0} and Ti 3d{sup 1} systems reveals the presence of different types of electronic states with Ti 3d character, i.e., oxygen vacancy induced, trapped in-gap states and itinerant states contributing to the 2DES. Exposure to low doses of oxygen during irradiation allows for the reversible manipulation of the oxygen stoichiometry, thus revealing the presence of an oxygen vacancy-induced state, which is characteristic for this spinel/perovskite interface.

  2. Intercalation assembly of Li{sub 3}VO{sub 4} nanoribbons/graphene sandwich-structured composites with enhanced oxygen reduction catalytic performance

    Energy Technology Data Exchange (ETDEWEB)

    Huang, K.; Ling, Q.N.; Huang, C.H.; Bi, K. [State Key Laboratory of Information Photonics and Optical Communications & School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Wang, W.J.; Yang, T.Z. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Lu, Y.K. [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); Liu, J., E-mail: liujun4982004@csu.edu.cn [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); Zhang, R.; Fan, D.Y.; Wang, Y.G. [State Key Laboratory of Information Photonics and Optical Communications & School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Lei, Ming, E-mail: mlei@bupt.edu.cn [State Key Laboratory of Information Photonics and Optical Communications & School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

    2015-10-15

    Novel sandwich-like nanocomposites of alternative stacked ultrathin Li{sub 3}VO{sub 4} nanoribbons and graphene sheets (LVO-G) were successfully developed by a facile intercalation assembly method with a post heating treatment. The characterization results demonstrate that the average size of the Li{sub 3}VO{sub 4} nanoribbons with a non-layered crystal structure is a few micrometers in length, 50–100 nm in width and a few atomic layers in height. The addition of graphene sheets can modify the preferred orientation of the Li{sub 3}VO{sub 4} nanoribbons from (110) to (011) plane and restrict the growth of impurity phase at the same time. In addition, EIS analysis has also verified the reduced resistance and thus the enhance conductivity of LVO-G nanocomposites compared with bare Li{sub 3}VO{sub 4} nanoribbons. What's more, the electrocatalytic performances of these novel LVO-G nanocomposites for oxygen reduction reaction (ORR) in alkaline solution are further investigated by cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry test. It is found that the enhanced activity and stability of LVO-G can be attributed to the synergistic effect between the Li{sub 3}VO{sub 4} nanoribbons and graphene sheets with a larger reduction current density and a smaller onset potential value for LVO-G25 compared with LVO-G50 due to the change of components. - Highlights: • Novel sandwich-structured LVO-G by a facile intercalation assembly method. • Addition of G sheets can modify the preferred orientation of Li{sub 3}VO{sub 4} nanoribbon. • Enhanced ORR activity and stability due to synergistic effect are demonstrated.

  3. Oxygen vacancy induces self-doping effect and metalloid LSPR in non-stoichiometric tungsten suboxide synergistically contributing to the enhanced photoelectrocatalytic performance of WO3-x/TiO2-x heterojunction.

    Science.gov (United States)

    Huang, Weicheng; Wang, Jinxin; Bian, Lang; Zhao, Chaoyue; Liu, Danqing; Guo, Chongshen; Yang, Bin; Cao, Wenwu

    2018-06-27

    A WO3-x/TiO2-x nanotube array (NTA) heterojunction photoanode was strategically designed to improve photoelectrocatalytic (PEC) performance by establishing a synergistic vacancy-induced self-doping effect and localized surface plasmon resonance (LSPR) effect of metalloid non-stoichiometric tungsten suboxide. The WO3-x/TiO2-x NTA heterojunction photoanode was synthesized through a successive process of anodic oxidation to form TiO2 nanotube arrays, magnetron sputtering to deposit metalloid WO3-x, and post-hydrogen reduction to engender oxygen vacancy in TiO2-x as well as crystallization. On the merits of such a synergistic effect, WO3-x/TiO2-x shows higher light-harvesting ability, stronger photocurrent response, and resultant improved photoelectrocatalytic performance than the contrast of WO3-x/TiO2, WO3/TiO2 and TiO2, confirming the importance of oxygen vacancies in improving PEC performance. Theoretical calculation based on density functional theory was applied to investigate the electronic structural features of samples and reveal how the oxygen vacancy determines the optical property. The carrier density tuning mechanism and charge transfer model were considered to be associated with the synergistic effect of self-doping and metalloid LSPR effect in the WO3-x/TiO2-x NTA.

  4. Reactive oxygen species generation in aqueous solutions containing GdVO4:Eu3+ nanoparticles and their complexes with methylene blue

    Science.gov (United States)

    Hubenko, Kateryna; Yefimova, Svetlana; Tkacheva, Tatyana; Maksimchuk, Pavel; Borovoy, Igor; Klochkov, Vladimir; Kavok, Nataliya; Opolonin, Oleksander; Malyukin, Yuri

    2018-04-01

    It this letter, we report the study of free radicals and reactive oxygen species (ROS) generation in water solutions containing gadolinium orthovanadate GdVO4:Eu3+ nanoparticles (VNPs) and their complexes with methylene blue (MB) photosensitizer. The catalytic activity was studied under UV-Vis and X-ray irradiation by three methods (conjugated dienes test, OH· radical, and singlet oxygen detection). It has been shown that the VNPs-MB complexes reveal high efficiency of ROS generation under UV-Vis irradiation associated with both high efficiency of OH· radicals generation by VNPs and singlet oxygen generation by MB due to nonradiative excitation energy transfer from VNPs to MB molecules. Contrary to that under X-ray irradiation, the strong OH . radicals scavenging by VNPs has been observed.

  5. Mixed oxygen ion/electron-conducting ceramics for oxygen separation

    Energy Technology Data Exchange (ETDEWEB)

    Stevenson, J.W.; Armstrong, T.R.; Armstrong, B.L. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-08-01

    Mixed oxygen ion and electron-conducting ceramics are unique materials that can passively separate high purity oxygen from air. Oxygen ions move through a fully dense ceramic in response to an oxygen concentration gradient, charge-compensated by an electron flux in the opposite direction. Compositions in the system La{sub 1{minus}x}M{sub x}Co{sub 1{minus}y{minus}z}Fe{sub y}N{sub z}O{sub 3{minus}{delta}}, perovskites where M=Sr, Ca, and Ba, and N=Mn, Ni, Cu, Ti, and Al, have been prepared and their electrical, oxygen permeation, oxygen vacancy equilibria, and catalytic properties evaluated. Tubular forms, disks, and asymmetric membrane structures, a thin dense layer on a porous support of the same composition, have been fabricated for testing purposes. In an oxygen partial gradient, the passive oxygen flux through fully dense structures was highly dependent on composition. An increase in oxygen permeation with increased temperature is attributed to both enhanced oxygen vacancy mobility and higher vacancy populations. Highly acceptor-doped compositions resulted in oxygen ion mobilities more than an order of magnitude higher than yttria-stabilized zirconia. The mixed conducting ceramics have been utilized in a membrane reactor configuration to upgrade methane to ethane and ethylene. Conditions were established to balance selectivity and throughput in a catalytic membrane reactor constructed from mixed conducting ceramics.

  6. Simultaneous sampling of tissue oxygenation and oxygen consumption in skeletal muscle.

    Science.gov (United States)

    Nugent, William H; Song, Bjorn K; Pittman, Roland N; Golub, Aleksander S

    2016-05-01

    Under physiologic conditions, microvascular oxygen delivery appears to be well matched to oxygen consumption in respiring tissues. We present a technique to measure interstitial oxygen tension (PISFO2) and oxygen consumption (VO2) under steady-state conditions, as well as during the transitions from rest to activity and back. Phosphorescence Quenching Microscopy (PQM) was employed with pneumatic compression cycling to achieve 1 to 10 Hz sampling rates of interstitial PO2 and simultaneous recurrent sampling of VO2 (3/min) in the exteriorized rat spinotrapezius muscle. The compression pressure was optimized to 120-130 mmHg without adverse effect on the tissue preparation. A cycle of 5s compression followed by 15s recovery yielded a resting VO2 of 0.98 ± 0.03 ml O2/100 cm(3)min while preserving microvascular oxygen delivery. The measurement system was then used to assess VO2 dependence on PISFO2 at rest and further tested under conditions of isometric muscle contraction to demonstrate a robust ability to monitor the on-kinetics of tissue respiration and the compensatory changes in PISFO2 during contraction and recovery. The temporal and spatial resolution of this approach is well suited to studies seeking to characterize microvascular oxygen supply and demand in thin tissues. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Effects of structure and oxygen flow rate on the photo-response of amorphous IGZO-based photodetector devices

    Science.gov (United States)

    Jang, Jun Tae; Ko, Daehyun; Choi, Sungju; Kang, Hara; Kim, Jae-Young; Yu, Hye Ri; Ahn, Geumho; Jung, Haesun; Rhee, Jihyun; Lee, Heesung; Choi, Sung-Jin; Kim, Dong Myong; Kim, Dae Hwan

    2018-02-01

    In this study, we investigated how the structure and oxygen flow rate (OFR) during the sputter-deposition affects the photo-responses of amorphous indium-gallium-zinc-oxide (a-IGZO)-based photodetector devices. As the result of comparing three types of device structures with one another, which are a global Schottky diode, local Schottky diode, and thin-film transistor (TFT), the IGZO TFT with the gate pulse technique suppressing the persistent photoconductivity (PPC) is the most promising photodetector in terms of a high photo-sensitivity and uniform sensing characteristic. In order to analyze the IGZO TFT-based photodetectors more quantitatively, the time-evolution of sub-gap density-of-states (DOS) was directly observed under photo-illumination and consecutively during the PPC-compensating period with applying the gate pulse. It shows that the increased ionized oxygen vacancy (VO2+) defects under photo-illumination was fully recovered by the positive gate pulse and even overcompensated by additional electron trapping. Based on experimentally extracted sub-gap DOS, the origin on PPC was successfully decomposed into the hole trapping and the VO ionization. Although the VO ionization is enhanced in lower OFR (O-poor) device, the PPC becomes more severe in high OFR (O-rich) device because the hole trapping dominates the PPC in IGZO TFT under photo-illumination rather than the VO ionization and more abundant holes are trapped into gate insulator and/or interface in O-rich TFTs. Similarly, the electron trapping during the PPC-compensating period with applying the positive gate pulse becomes more prominent in O-rich TFTs. It is attributed to more hole/electron traps in the gate insulator and/or interface, which is associated with oxygen interstitials, or originates from the ion bombardment-related lower quality gate oxide in O-rich devices.

  8. New Methods for Processing and Quantifying VO2 Kinetics to Steady State: VO2 Onset Kinetics

    Directory of Open Access Journals (Sweden)

    Craig R. McNulty

    2017-09-01

    Full Text Available Current methods of oxygen uptake (VO2 kinetics data handling may be too simplistic for the complex physiology involved in the underlying physiological processes. Therefore, the aim of this study was to quantify the VO2 kinetics to steady state across the full range of sub-ventilatory threshold work rates, with a particular focus on the VO2 onset kinetics. Ten healthy, moderately trained males participated in five bouts of cycling. Each bout involved 10 min at a percentage of the subject's ventilation threshold (30, 45, 60, 75, 90% from unloaded cycling. The VO2 kinetics was quantified using the conventional mono-exponential time constant (tau, τ, as well as the new methods for VO2 onset kinetics. Compared to linear modeling, non-linear modeling caused a deterioration of goodness of fit (main effect, p < 0.001 across all exercise intensities. Remainder kinetics were also improved using a modified application of the mono-exponential model (main effect, p < 0.001. Interestingly, the slope from the linear regression of the onset kinetics data is similar across all subjects and absolute exercise intensities, and thereby independent of subject fitness and τ. This could indicate that there are no functional limitations between subjects during this onset phase, with limitations occurring for the latter transition to steady state. Finally, the continuing use of mono-exponential modeling could mask important underlying physiology of more instantaneous VO2 responses to steady state. Consequently, further research should be conducted on this new approach to VO2 onset kinetics.

  9. Effect of oxygen vacancy induced by pulsed magnetic field on the room-temperature ferromagnetic Ni-doped ZnO synthesized by hydrothermal method

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, Min [Shanghai University, Laboratory for Microstructures, School of Materials Science and Engineering, 149 Yanchang Road, 200072 Shanghai (China); Li, Ying, E-mail: liying62@shu.edu.cn [Shanghai University, Laboratory for Microstructures, School of Materials Science and Engineering, 149 Yanchang Road, 200072 Shanghai (China); Tariq, Muhammad; Hu, Yemin; Li, Wenxian; Zhu, Mingyuan; Jin, Hongmin [Shanghai University, Laboratory for Microstructures, School of Materials Science and Engineering, 149 Yanchang Road, 200072 Shanghai (China); Li, Yibing [School of Chemistry, The University of New South Wales, Sydney, NSW, 2052 (Australia)

    2016-08-05

    Room temperature ferromagnetic 2% Ni doped ZnO rods were synthesized by high pulsed magnetic field-assisted hydrothermal method. A detailed study on the effect of high pulsed magnetic field on morphology, structural and magnetic properties of the ZnO rods has been carried out systematically by varying the intensity of field from 0 to 4 T. X-ray diffraction, Energy-dispersive spectroscopy measurements, and Raman spectra analysis suggest that all the samples have hexagonal wurtzite structure without detectable impurity. Field emission scanning electron microscopy images indicate that the particle size of samples decrease with increasing intensity of field. High resolution transmission electron microscopy observation ensures that the Ni ions addition do not change the wurtzite host matrix. X-ray photoelectron spectroscopy confirms the incorporation of Ni elements as divalent state and the dominant presence of oxygen vacancies in samples fabricated under 4 T pulsed magnetic field. Hysteresis loops demonstrate that the saturation magnetization increased regularly with the mounting magnetic field. On the framework of bound magnetic polaron model, the rising content of oxygen vacancies, as donor defect, lead to the stronger ferromagnetism in samples with pulsed magnetic field. Our findings provide a new insight for tuning the defect density by precisely controlling the intensity of field in order to get the desired magnetic behavior at room temperature. - Graphical abstract: This figure shows the magnetization versus magnetic field curves for 2%Ni doped ZnO as prepared with 0, 1, 2, 3 and 4 T pulsed magnetic field at 290 K. For 0 T sample, no ferromagnetic response is observed. But all the samples synthesized with field were well-defined hysteresis loops. The saturation magnetization estimated from the hysteresis loop come out to be ∼0.0024, 0.0023, 0.0036 and 0.0061 emu/g for 1 T, 2 T, 3 T and 4 T samples, respectively. As shown in the curves, the room

  10. Human mitochondrial haplogroup H: the highest VO2max consumer--is it a paradox?

    Science.gov (United States)

    Martínez-Redondo, Diana; Marcuello, Ana; Casajús, José A; Ara, Ignacio; Dahmani, Yahya; Montoya, Julio; Ruiz-Pesini, Eduardo; López-Pérez, Manuel J; Díez-Sánchez, Carmen

    2010-03-01

    Mitochondrial background has been demonstrated to influence maximal oxygen uptake (VO(2max), in mLkg(-1)min(-1)), but this genetic influence can be compensated for by regular exercise. A positive correlation among electron transport chain (ETC) coupling, ATP and reactive oxygen species (ROS) production has been established, and mitochondrial variants have been reported to show differences in their ETC performance. In this study, we examined in detail the VO(2max) differences found among mitochondrial haplogroups. We recruited 81 healthy male Spanish Caucasian individuals and determined their mitochondrial haplogroup. Their VO(2max) was determined using incremental cycling exercise (ICE). VO(2max) was lower in J than in non-J haplogroup individuals (P=0.04). The H haplogroup was responsible for this difference (VO(2max); J vs. H; P=0.008) and this group also had significantly higher mitochondrial oxidative damage (mtOD) than the J haplogroup (P=0.04). In agreement with these results, VO(2max) and mtOD were positively correlated (P=0.01). Given that ROS production is the major contributor to mtOD and consumes four times more oxygen per electron than the ETC, our results strongly suggest that ROS production is responsible for the higher VO(2max) found in the H variant. These findings not only contribute to a better understanding of the mechanisms underneath VO(2max), but also help to explain some reported associations between mitochondrial haplogroups and mtOD with longevity, sperm motility, premature aging and susceptibility to different pathologies.

  11. Enhanced photoluminescence and Raman properties of Al-Doped ZnO nanostructures prepared using thermal chemical vapor deposition of methanol assisted with heated brass.

    Directory of Open Access Journals (Sweden)

    Tamil Many K Thandavan

    Full Text Available Vapor phase transport (VPT assisted by mixture of methanol and acetone via thermal evaporation of brass (CuZn was used to prepare un-doped and Al-doped zinc oxide (ZnO nanostructures (NSs. The structure and morphology were characterized by field emission scanning electron microscopy (FESEM and x-ray diffraction (XRD. Photoluminescence (PL properties of un-doped and Al-doped ZnO showed significant changes in the optical properties providing evidence for several types of defects such as zinc interstitials (Zni, oxygen interstitials (Oi, zinc vacancy (Vzn, singly charged zinc vacancy (VZn-, oxygen vacancy (Vo, singly charged oxygen vacancy (Vo+ and oxygen anti-site defects (OZn in the grown NSs. The Al-doped ZnO NSs have exhibited shifted PL peaks at near band edge (NBE and red luminescence compared to the un-doped ZnO. The Raman scattering results provided evidence of Al doping into the ZnO NSs due to peak shift from 145 cm-1 to an anomalous peak at 138 cm-1. Presence of enhanced Raman signal at around 274 and 743 cm-1 further confirmed Al in ZnO NSs. The enhanced D and G band in all Al-doped ZnO NSs shows possible functionalization and doping process in ZnO NSs.

  12. Enhanced photoluminescence and Raman properties of Al-Doped ZnO nanostructures prepared using thermal chemical vapor deposition of methanol assisted with heated brass.

    Science.gov (United States)

    Thandavan, Tamil Many K; Gani, Siti Meriam Abdul; San Wong, Chiow; Md Nor, Roslan

    2015-01-01

    Vapor phase transport (VPT) assisted by mixture of methanol and acetone via thermal evaporation of brass (CuZn) was used to prepare un-doped and Al-doped zinc oxide (ZnO) nanostructures (NSs). The structure and morphology were characterized by field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). Photoluminescence (PL) properties of un-doped and Al-doped ZnO showed significant changes in the optical properties providing evidence for several types of defects such as zinc interstitials (Zni), oxygen interstitials (Oi), zinc vacancy (Vzn), singly charged zinc vacancy (VZn-), oxygen vacancy (Vo), singly charged oxygen vacancy (Vo+) and oxygen anti-site defects (OZn) in the grown NSs. The Al-doped ZnO NSs have exhibited shifted PL peaks at near band edge (NBE) and red luminescence compared to the un-doped ZnO. The Raman scattering results provided evidence of Al doping into the ZnO NSs due to peak shift from 145 cm-1 to an anomalous peak at 138 cm-1. Presence of enhanced Raman signal at around 274 and 743 cm-1 further confirmed Al in ZnO NSs. The enhanced D and G band in all Al-doped ZnO NSs shows possible functionalization and doping process in ZnO NSs.

  13. Transmission of reactive pulsed laser deposited VO{sub 2} films in the THz domain

    Energy Technology Data Exchange (ETDEWEB)

    Émond, Nicolas; Hendaoui, Ali; Ibrahim, Akram; Al-Naib, Ibraheem; Ozaki, Tsuneyuki; Chaker, Mohamed, E-mail: chaker@emt.inrs.ca

    2016-08-30

    Highlights: • Synthesis of vanadium dioxide (VO{sub 2}) thin films as a function of oxygen pressure (2–25 mTorr) using Reactive Pulsed Laser Deposition (RPLD). • Characterization of RPLD-grown VO{sub 2} thin films in the THz frequency range. • THz switches and/or sensors require VO{sub 2} films deposited at low oxygen pressure (i.e. low transition temperature, large amplitude contrast of THz transmission, narrow hysteresis width). • THz optical memory applications require VO{sub 2} films deposited at high oxygen pressure (broad hysteresis width). - Abstract: This work reports on the characteristics of the insulator-to-metal transition (IMT) of reactive pulsed laser deposited vanadium dioxide (VO{sub 2}) films in the terahertz (THz) frequency range, namely the transition temperature T{sub IMT}, the amplitude contrast of the THz transmission over the IMT ΔA, the transition sharpness ΔT and the hysteresis width ΔH. XRD analysis shows the sole formation of VO{sub 2} monoclinic structure with an enhancement of (011) preferential orientation when varying the O{sub 2} pressure (P{sub O2}) during the deposition process from 2 to 25 mTorr. THz transmission measurements as a function of temperature reveal that VO{sub 2} films obtained at low P{sub O2} exhibit low T{sub IMT}, large ΔA, and narrow ΔH. Increasing P{sub O2} results in VO{sub 2} films with higher T{sub IMT}, smaller ΔA, broader ΔH and asymmetric hysteresis loop. The good control of the VO{sub 2} IMT features in the THz domain could be further exploited for the development of advanced smart devices, such as ultrafast switches, modulators, memories and sensors.

  14. Enhancement of oxygen vacancies and solar photocatalytic activity of zinc oxide by incorporation of nonmetal

    International Nuclear Information System (INIS)

    Patil, Ashokrao B.; Patil, Kashinath R.; Pardeshi, Satish K.

    2011-01-01

    B-doped ZnO and N-doped ZnO powders have been synthesized by mechanochemical method and characterized by TG–DTA, XRD, SEM–EDX, XPS, UV–visible and photoluminescence (PL) spectra. X-ray diffraction data suggests the hexagonal wurtzite structure for modified ZnO crystallites and the incorporation of nonmetal expands the lattice constants of ZnO. The room temperature PL spectra suggest more number of oxygen vacancies exist in nonmetal-doped ZnO than that of undoped zinc oxide. XPS analysis shows the substitution of some of the O atoms of ZnO by nonmetal atoms. Solar photocatalytic activity of B-doped ZnO, N-doped ZnO and undoped ZnO was compared by means of oxidative photocatalytic degradation (PCD) of Bisphenol A (BPA). B-doped ZnO showed better solar PCD efficiency as compare to N-doped ZnO and undoped ZnO. The PCD of BPA follows first order reaction kinetics. The detail mechanism of PCD of Bisphenol A was proposed with the identification of intermediates such as hydroquinone, benzene-1,2,4-triol and 4-(2-hydroxypropan-2-yl) phenol. - Graphical Abstract: B-doped ZnO and N-doped ZnO synthesized by mechanochemical method were characterized by various techniques. Solar photocatalytic degradation of Bisphenol-A is in the order of B-ZnO>N-ZnO>ZnO. Highlights: ► B-doped ZnO and N-doped ZnO powders have been synthesized by mechanochemical method. ► PL spectra suggest oxygen vacancies are in order of B-doped ZnO>N-doped ZnO>ZnO. ► Solar PCD efficiency is in order of B-doped ZnO>N-doped ZnO>ZnO for Bisphenol A.

  15. Zinc Vacancy-Induced Room-Temperature Ferromagnetism in Undoped ZnO Thin Films

    Directory of Open Access Journals (Sweden)

    Hongtao Ren

    2012-01-01

    Full Text Available Undoped ZnO thin films are prepared by polymer-assisted deposition (PAD and treated by postannealing at different temperatures in oxygen or forming gases (95%  Ar+5% H2. All the samples exhibit ferromagnetism at room temperature (RT. SQUID and positron annihilation measurements show that post-annealing treatments greatly enhance the magnetizations in undoped ZnO samples, and there is a positive correlation between the magnetization and zinc vacancies in the ZnO thin films. XPS measurements indicate that annealing also induces oxygen vacancies that have no direct relationship with ferromagnetism. Further analysis of the results suggests that the ferromagnetism in undoped ZnO is induced by Zn vacancies.

  16. The electrochemical catalytic activity of single-walled carbon nanotubes towards VO2+/VO2+ and V3+/V2+ redox pairs for an all vanadium redox flow battery

    International Nuclear Information System (INIS)

    Li Wenyue; Liu Jianguo; Yan Chuanwei

    2012-01-01

    Highlights: ► SWCNT shows excellent electrochemical catalytic activity towards VO 2 + /VO 2+ and V 3+ /V 2+ redox couples. ► The anodic reactions are more sensitive to the surface oxygen atom content change compared with the cathodic reactions. ► The enhanced battery performance clearly demonstrated that the SWCNT is suitable to be used as an electrode catalyst for VRFB. - Abstract: Single-walled carbon nanotube (SWCNT) was used as an electrode catalyst for an all vanadium redox flow battery (VRFB). The electrochemical property of SWCNT towards VO 2 + /VO 2+ and V 3+ /V 2+ was carefully characterized by cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS) measurements. The peak current values for these redox pairs were significantly higher on the modified glassy carbon electrode compared with those obtained on the bare electrode, suggesting the excellent electrochemical activity of the SWCNT. Moreover, it was proved that the anodic process was more dependent on the surface oxygen of the SWCNT than the cathodic process through changing its surface oxygen content. Detailed EIS analysis of different modified electrodes revealed that the charge and mass transfer processes were accelerated at the modified electrode–electrolyte interface, which could be ascribed to the large specific surface area, the surface defects and the oxygen functional groups of the SWCNT. The enhanced battery performance effectively demonstrated that the SWCNT was suitable to serve as an electrode catalyst for the VRFB.

  17. Transformation of point defects under annealing of neutron-irradiated Si and Si:Ge

    International Nuclear Information System (INIS)

    Pomozov, Yu.V.; Khirunenko, L.I.; Shakhovtsev, V.I.; Yashnik, V.I.

    1990-01-01

    Transformation of point radiation defects under isochronous annealing of neurton-irradaited Si and Si:Ge is studied. It is determined, that occurence of several new centers which produce A-centre range absorption bands is observed at annealing within 423-493 K temperature range. It is shown that vacancy and oxygen are included in the centers composition. It is found that VO centre transformation into VO 2 at annealing occurs via intermediate stage in contrast to that occuring in electron-irradiated crystals via VO direct diffusion to interstitial oxygen. Transformation of centers under Si ansd Si:Ge annealing occurs similarly

  18. Oxygen vacancy-induced room-temperature ferromagnetism in D—D neutron irradiated single-crystal TiO2 (001) rutile

    Science.gov (United States)

    Xu, Nan-Nan; Li, Gong-Ping; Pan, Xiao-Dong; Wang, Yun-Bo; Chen, Jing-Sheng; Bao, Liang-Man

    2014-10-01

    Remarkable room temperature ferromagnetism in pure single-crystal rutile TiO2 (001) samples irradiated by D—D neutron has been investigated. By combining X-ray diffraction and positron annihilation lifetime, the contracted lattice has been clearly identified in irradiated TiO2, where Ti4+ ions can be easily reduced to the state of Ti3+. As there were no magnetic impurities that could contaminate the samples during the whole procedure, some Ti3+ ions reside on interstitial or substituted sites accompanied by oxygen vacancies should be responsible for the ferromagnetism.

  19. Synergistic effect of oxygen vacancy and nitrogen doping on enhancing the photocatalytic activity of Bi{sub 2}O{sub 2}CO{sub 3} nanosheets with exposed {0 0 1} facets for the degradation of organic pollutants

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yafei [School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China); Zhu, Gangqiang, E-mail: zgq2006@snnu.edu.cn [School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China); Hojamberdiev, Mirabbos [School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China); Department of Natural and Mathematic Sciences, Turin Polytechnic University in Tashkent, Kichik Halqa Yo’li 17, Tashkent 100095 (Uzbekistan); Gao, Jianzhi [School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China); Hao, Jing [Xi' an Rejee Industry Development Co., Ltd., Xi’an 710016 (China); Zhou, Jianping; Liu, Peng [School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062 (China)

    2016-05-15

    Highlights: • Nitrogen-doped Bi{sub 2}O{sub 2}CO{sub 3} flower-like microstructures were synthesized by hydrothermal method. • Surface oxygen vacancy were obtained by irradiating the nitrogen-doped Bi{sub 2}O{sub 2}CO{sub 3} with UV light. • Photocatalytic activity was studied by degrading Rhodamine B. • A synergistic effect between oxygen vacancy and nitrogen doping in Bi{sub 2}O{sub 2}CO{sub 3}. - Abstract: Single-crystalline bare Bi{sub 2}O{sub 2}CO{sub 3} (BOC) nanosheets with exposed {0 0 1} facets and nitrogen-doped Bi{sub 2}O{sub 2}CO{sub 3} (NBOC) flower-like microstructures were synthesized by a simple hydrothermal method. The nitrogen-doped Bi{sub 2}O{sub 2}CO{sub 3} flower-like microstructures with oxygen vacancy (UV-NBOC) were obtained by irradiating the NBOC microstructures with UV light for 2 h in ethanol. The UV–vis diffuse reflectance spectra showed that the NBOC and UV-NBOC nanosheets exhibit an obvious red shift in light absorption band compared with the pure BOC nanosheets. Rhodamine B (RhB) was chosen as a model organic pollutant to verify the influence of oxygen vacancy and nitrogen doping on the photocatalytic activity of Bi{sub 2}O{sub 2}CO{sub 3} under simulated solar light irradiation. Judging from the kinetics of RhB photodegradation over the synthesized samples, a synergistic effect between oxygen vacancy and nitrogen doping was found with a remarkable increase (more than 10 and 2 times) in the photocatalytic activity of UV-NBOC compared with BOC and NBOC, respectively. Moreover, the UV-NBOC also exhibited an excellent cyclability and superior photocatalytic activity toward degradation of other organic pollutants (methylene blue, Congo red, Bisphenol A) under simulated solar light irradiation.

  20. High-temperature equilibrium vacancy formation in ceramic materials studied by positron annihilation

    International Nuclear Information System (INIS)

    Forster, M.; Claudy, W.; Hermes, H.; Major, J.; Schaefer, H.E.; Koch, M.; Maier, K.; Stoll, H.

    1992-01-01

    Positron lifetime measurements were used in order to study thermal vacancy formation in NiO, YBa 2 Cu 3 O 7-δ , α-Al 2 O 3 , MgO and 6H-SiC at high temperatures. In NiO two increases of the positron trapping rate at 450K and 1200K (po 2 =10 5 Pa) are attributed to the change of charge of neutral extrinsic Ni-vacancies (c ≅ 10 -4 ) into a negative charge state and to the nonstochiometric formation of charged Ni-vacancies at high temperatures. In YBa 2 Cu 3 O 7-δ the oxygen loss or uptake at T > 680K with an activation enthalpy of 1.03eV can be studied by the variation of the positron lifetime with temperature and oxygen partial pressure. In α-Al 2 O 3 the positrons are annihilated from the delocalized free state between 1000K and 2250K and no positron trapping of thermally formed vacancies was detected which may be understood in terms of the theoretically predicted low concentrations of thermal vacancies. In MgO and 6H-SiC positron lifetime measurements were performed up to temperatures of about 2000K

  1. Photoluminescence and Raman studies for the confirmation of oxygen vacancies to induce ferromagnetism in Fe doped Mn:ZnO compound

    Energy Technology Data Exchange (ETDEWEB)

    Das, J., E-mail: jayashree304@gmail.com [Department of Physics, Silicon Institute of Technology, Bhubaneswar 751024, Odisha (India); Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710 (South Africa); Mishra, D.K. [Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710 (South Africa); Department of Physics, Institute of Technical Education and Research, Siksha ‘O’ Anusandhan University, Khandagiri Square, Bhubaneswar 751030, Odisha (India); Srinivasu, V.V. [Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710 (South Africa); Sahu, D.R. [Amity Institute of Nanotechnology, Amity University, Noida (India); Roul, B.K. [Institute of Materials Science, Planetarium Building, Acharya Vihar, Bhubaneswar, Odisha (India)

    2015-05-15

    With a motivation to compare the magnetic property, we synthesised undoped, transition metal (TM) Mn doped and (Mn:Fe) co-doped ZnO ceramics in the compositions ZnO, Zn{sub 0.98}Mn{sub 0.02}O and Zn{sub 0.96}(Mn{sub 0.02}Fe{sub 0.02})O. Systematic investigations on the structural, microstructural, defect structure and magnetic properties of the samples were performed. Low temperature as well as room temperature ferromagnetism has been observed for all our samples, however, enhanced magnetisation at room temperature has been noticed when ZnO is co-doped with Fe along with Mn. Particularly the sample with the composition Zn{sub 0.96}Mn{sub 0.02}Fe{sub 0.02}O showed a magnetisation value more than double of the sample with composition Zn{sub 0.98}Mn{sub 0.02}O, indicating long range strong interaction between the magnetic impurities leading to higher ferromagnetic ordering. Raman and PL studies reveal presence of higher defects in form of oxygen vacancy clusters created in the sample due to Fe co doping. PL study also reveals enhanced luminescence efficiency in the co doped sample. Temperature dependent magnetisation study of this sample shows the spin freezing temperature around 39 K indicating the presence of small impurity phase of Mn{sub 2−x}Zn{sub x}O{sub 3} type. Electron Spin Resonance signal obtained supports ferromagnetic state in the co doped sample. Enhancement of magnetisation is attributed to interactions mediated by magnetic impurities through large number of oxygen vacancies created by Fe{sup 3+} ions forming bound magnetic polarons (BMP) and facilitating long range ferromagnetic ordering in the co- doped system. - Highlights: • Comparison of magnetic property of ZnO, Zn{sub 0.98}Mn {sub 0.02}O and Zn{sub 0.96}(Mn{sub 0.02}Fe{sub 0.02})O. • Observation of enhanced magnetisation at room temperature in (Mn,Fe) doped ZnO. • Raman and PL studies reveal presence of higher oxygen vacancy clusters. • Electron Spin Resonance signal supports

  2. Stability of V2O5 Supported on Titania in the Presence of Water, Bulk Oxygen Vacancies, and Adsorbed Oxygen Atoms

    DEFF Research Database (Denmark)

    Kristoffersen, Henrik Høgh; Neilson, Hunter L.; Buratto, Steven K.

    2017-01-01

    ). In the case of oxidative dehydrogenation of alkanes and methanol, the reaction produces water, oxygen vacancies, and hydrogen atoms bound to the surface. For this article we use density functional theory to examine how the presence of these species on the surface affects a V2O5 cluster, which we assume......A catalyst consisting of vanadium oxide submonolayers supported on rutile titanium dioxide is used for a variety of reactions. One important question is the difference between the activity of monomeric clusters (having one vanadium atom) and polymeric clusters (having more than one vanadium atom...

  3. Investigation of the oxygen-vacancy (A-center) defect complex profile in neutron irradiated high resistivity silicon junction particle detectors

    International Nuclear Information System (INIS)

    Li, Zheng; Kraner, H.W.; Verbitskaya, E.; Eremin, V.; Ivanov, A.; Rubinelli, F.A.; Fonash, S.J.

    1992-02-01

    Distributions of the A-center (oxygen-vacancy) in neutron silicon detectors have been studied using Deep Level Transient Spectroscopy. A-centers have been found to be nearly uniformly distributed in the silicon water depth for medium resistivity (0.1 - 0.2 kΩ-cm) silicon detectors. A positive filling pulse was needed to detect the A-centers in high resistivity (>4 kΩ-cm) silicon detectors, and this effect was found to be dependent on the oxidation temperature. A discussion of this effect is presented. 16 refs

  4. Switchable diode effect in oxygen vacancy-modulated SrTiO{sub 3} single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Xinqiang; Shuai, Yao; Wu, Chuangui; Luo, Wenbo; Sun, Xiangyu; Zeng, Huizhong; Bai, Xiaoyuan; Gong, Chaoguan; Jian, Ke; Zhang, Wanli [University of Electronic Science and Technology of China, State Key Laboratory of Electronic Thin Films and Integrated Devices, Chengdu (China); Zhang, Lu; Guo, Hongliang [University of Electronic Science and Technology of China, The Center for Robotics, Chengdu (China); Tian, Benlang [26th Institute of China Electronics Technology Group Corporation, Chongqing (China)

    2017-09-15

    SrTiO{sub 3} (STO) single crystal wafer was annealed in vacuum, and co-planar metal-insulator-metal structure of Pt/Ti/STO/Ti/Pt were formed by sputtering Pt/Ti electrodes onto the surface of STO after annealing. The forming-free resistive switching behavior with self-compliance property was observed in the sample. The sample showed switchable diode effect, which is explained by a simple model that redistribution of oxygen vacancies (OVs) under the external electric field results in the formation of n-n{sup +} junction or n{sup +}-n junction (n donated n-type semiconductor; n{sup +} donated heavily doped n-type semiconductor). The self-compliance property is also interpreted by the formation of n-n{sup +}/n{sup +}-n junction caused by the migration of the OVs under the electric field. (orig.)

  5. Room temperature alcohol sensing by oxygen vacancy controlled TiO2 nanotube array

    International Nuclear Information System (INIS)

    Hazra, A.; Dutta, K.; Bhowmik, B.; Bhattacharyya, P.; Chattopadhyay, P. P.

    2014-01-01

    Oxygen vacancy (OV) controlled TiO 2 nanotubes, having diameters of 50–70 nm and lengths of 200–250 nm, were synthesized by electrochemical anodization in the mixed electrolyte comprising NH 4 F and ethylene glycol with selective H 2 O content. The structural evolution of TiO 2 nanoforms has been studied by field emission scanning electron microscopy. Variation in the formation of OVs with the variation of the structure of TiO 2 nanoforms has been evaluated by photoluminescence and X-ray photoelectron spectroscopy. The sensor characteristics were correlated to the variation of the amount of induced OVs in the nanotubes. The efficient room temperature sensing achieved by the control of OVs of TiO 2 nanotube array has paved the way for developing fast responding alcohol sensor with corresponding response magnitude of 60.2%, 45.3%, and 36.5% towards methanol, ethanol, and 2-propanol, respectively.

  6. Enhanced room temperature ferromagnetism in electrodeposited Co-doped ZnO nanostructured thin films by controlling the oxygen vacancy defects

    Energy Technology Data Exchange (ETDEWEB)

    Simimol, A. [Nanomaterials Research Lab, Surface Engineering Division, CSIR-National Aerospace Laboratories, Post Bag No. 1779, Bangalore 560017 (India); Department of Physics, National Institute of Technology Calicut, Calicut 673601 (India); Anappara, Aji A. [Department of Physics, National Institute of Technology Calicut, Calicut 673601 (India); Greulich-Weber, S. [Department of Physics, Nanophotonic Materials, Faculty of Science, University of Paderborn, 33095 Paderborn (Germany); Chowdhury, Prasanta [Nanomaterials Research Lab, Surface Engineering Division, CSIR-National Aerospace Laboratories, Post Bag No. 1779, Bangalore 560017 (India); Barshilia, Harish C., E-mail: harish@nal.res.in

    2015-06-07

    We report the growth of un-doped and cobalt doped ZnO nanostructures fabricated on FTO coated glass substrates using electrodeposition method. A detailed study on the effects of dopant concentration on morphology, structural, optical, and magnetic properties of the ZnO nanostructures has been carried out systematically by varying the Co concentration (c.{sub Co}) from 0.01 to 1 mM. For c.{sub Co }≤ 0.2 mM, h-wurtzite phase with no secondary phases of Co were present in the ZnO nanostructures. For c.{sub Co} ≤ 0.2 mM, the photoluminescence spectra exhibited a decrease in the intensity of ultraviolet emission as well as band-gap narrowing with an increase in dopant concentration. All the doped samples displayed a broad emission in the visible range and its intensity increased with an increase in Co concentration. It was found that the defect centers such as oxygen vacancies and zinc interstitials were the source of the visible emission. The X-ray photoelectron spectroscopy studies revealed, Co was primarily in the divalent state, replacing the Zn ion inside the tetrahedral crystal site of ZnO without forming any cluster or secondary phases of Co. The un-doped ZnO nanorods exhibited diamagnetic behavior and it remained up to a c.{sub Co} of 0.05 mM, while for c.{sub Co }> 0.05 mM, the ZnO nanostructures exhibited ferromagnetic behavior at room temperature. The coercivity increased to 695 G for 0.2 mM Co-doped sample and then it decreased for c.{sub Co }> 0.2 mM. Our results illustrate that up to a threshold concentration of 0.2 mM, the strong ferromagnetism is due to the oxygen vacancy defects centers, which exist in the Co-doped ZnO nanostructures. The origin of strong ferromagnetism at room temperature in Co-doped ZnO nanostructures is attributed to the s-d exchange interaction between the localized spin moments resulting from the oxygen vacancies and d electrons of Co{sup 2+} ions. Our findings provide a new insight for tuning the

  7. Large modification in insulator-metal transition of VO{sub 2} films grown on Al{sub 2}O{sub 3} (001) by high energy ion irradiation in biased reactive sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Azhan, Nurul Hanis; Okimura, Kunio, E-mail: okifn@keyaki.cc.u-tokai.ac.jp [Graduate School of Science and Technology, Tokai University, Hiratsuka 259-1292 (Japan); Ohtsubo, Yoshiyuki; Kimura, Shin-ichi [Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871 (Japan); Zaghrioui, Mustapha; Sakai, Joe [GREMAN, UMR 7347 CNRS, Université François Rabelais de Tours, Parc de Grandmont, 37200 Tours (France)

    2016-02-07

    High energy ion irradiation in biased reactive sputtering enabled significant modification of insulator-metal transition (IMT) properties of VO{sub 2} films grown on Al{sub 2}O{sub 3} (001). Even at a high biasing voltage with mean ion energy of around 325 eV induced by the rf substrate biasing power of 40 W, VO{sub 2} film revealed low IMT temperature (T{sub IMT}) at 309 K (36 °C) together with nearly two orders magnitude of resistance change. Raman measurements from −193 °C evidenced that the monoclinic VO{sub 2} lattice begins to transform to rutile-tetragonal lattice near room temperature. Raman spectra showed the in-plane compressive stress in biased VO{sub 2} films, which results in shortening of V–V distance along a-axis of monoclinic structure, a{sub M}-axis (c{sub R}-axis) and thus lowering the T{sub IMT}. In respect to that matter, significant effects in shortening the in-plane axis were observed through transmission electron microscopy observations. V2p{sub 3/2} spectra from XPS measurements suggested that high energy ion irradiation also induced oxygen vacancies and resulted for an early transition onset and rather broader transition properties. Earlier band gap closing against the temperature in VO{sub 2} film with higher biasing power was also probed by ultraviolet photoelectron spectroscopy. Present results with significant modification of IMT behavior of films deposited at high-energy ion irradiation with T{sub IMT} near the room temperature could be a newly and effective approach to both exploring mechanisms of IMT and further applications of this material, due to the fixed deposition conditions and rather thicker VO{sub 2} films.

  8. Positron annihilation study of vacancy-type defects in fast-neutron-irradiated MgO·nAl2O3

    Science.gov (United States)

    Rahman, Abu Zayed Mohammad Saliqur; Li, Zhuoxin; Cao, Xingzhong; Wang, Baoyi; Wei, Long; Xu, Qiu; Atobe, Kozo

    2014-09-01

    The positron lifetimes of fast-neutron-irradiated MgO·nAl2O3 single crystals were measured to investigate the formation of cation vacancies. Al monovacancy was possibly observed in samples irradiated by fast neutrons at ultra-low temperatures. Additionally, vacancy-oxygen complex centers were possibly observed in samples irradiated at higher temperatures and fast neutron fluences. Coincidence Doppler broadening (CDB) spectra were measured to obtain information regarding the vicinity of vacancy-type defects. A peak at approximately 11 × 10-3 m0c was observed, which may be due to the presence of oxygen atoms in the neighborhood of the vacancies.

  9. Multi-scale modeling of interaction between vacancies and alloying elements in ferritic alloys

    International Nuclear Information System (INIS)

    Barouh, Caroline

    2015-01-01

    This PhD thesis is devoted to the study of interaction between vacancies and alloying elements in Oxide Dispersion Strengthened (ODS) steels, which are promising candidate materials for future nuclear reactors. This work is based on multi-scale modeling of a simplified system composed by oxygen, yttrium and titanium atoms and vacancies in an α-iron lattice. We particularly focused on the role of vacancies which are created in excess during the fabrication of these steels. The stability and mobility of vacancy-solute clusters have been examined using ab initio calculations for oxygen, on one hand, which has been systematically compared to carbon and nitrogen, interstitial solutes frequently present in iron-based materials, and, on the other hand, for substitutional solutes: titanium and yttrium. The three interstitial solutes show very similar energetic and kinetic behaviors. The impact of small mobile vacancy-solute clusters has been verified using a cluster dynamics model based on our ab initio results. It has been thus demonstrated that with over-saturation of vacancies, diffusion of interstitial solutes may be accelerated, while substitutional solutes do not become necessarily faster. These conclusions are consistent with existing experimental observations. All these results have been then used to complete our understanding of nano-clusters formation mechanisms. It appeared that the relative mobility of yttrium and titanium, as well as the number of potential nuclei to form nanoparticles strongly depend on the total vacancy concentration in the system. (author) [fr

  10. Increases in .VO2max with "live high-train low" altitude training: role of ventilatory acclimatization.

    Science.gov (United States)

    Wilhite, Daniel P; Mickleborough, Timothy D; Laymon, Abigail S; Chapman, Robert F

    2013-02-01

    The purpose of this study was to estimate the percentage of the increase in whole body maximal oxygen consumption (.VO(2max)) that is accounted for by increased respiratory muscle oxygen uptake after altitude training. Six elite male distance runners (.VO(2max) = 70.6 ± 4.5 ml kg(-1) min(-1)) and one elite female distance runner (.VO(2max)) = 64.7 ml kg(-1) min(-1)) completed a 28-day "live high-train low" training intervention (living elevation, 2,150 m). Before and after altitude training, subjects ran at three submaximal speeds, and during a separate session, performed a graded exercise test to exhaustion. A regression equation derived from published data was used to estimate respiratory muscle .VO(2) (.VO(2RM)) using our ventilation (.VE) values. .VO(2RM) was also estimated retrospectively from a larger group of distance runners (n = 22). .VO(2max) significantly (p altitude (196 ± 59 ml min(-1)), while (.VE) at .VO(2max) also significantly (p altitude (201 ± 36 ml min(-1)), along with a 10.8 ± 2.1 l min(-1) increase in (.VE), thus requiring an estimated 27 % of Δ .VO(2max) Our data suggest that a substantial portion of the improvement in .VO(2max) with chronic altitude training goes to fuel the respiratory muscles as opposed to the musculature which directly contributes to locomotion. Consequently, the time-course of decay in ventilatory acclimatization following return to sea-level may have an impact on competitive performance.

  11. Room Temperature Optical Constants and Band Gap Evolution of Phase Pure M1-VO2 Thin Films Deposited at Different Oxygen Partial Pressures by Reactive Magnetron Sputtering

    Directory of Open Access Journals (Sweden)

    Meng Jiang

    2014-01-01

    Full Text Available Spectroscopic ellipsometry study was employed for phase pure VO2(M1 thin films grown at different oxygen partial pressures by reactive magnetron sputtering. The optical constants of the VO2(M1 thin films have been determined in a photon energy range between 0.73 and 5.05 eV. The near-infrared extinction coefficient and optical conductivity of VO2(M1 thin films rapidly increase with decreasing O2-Ar ratios. Moreover, two electronic transitions can be uniquely assigned. The energy gaps correlated with absorption edge (E1 at varied O2-Ar ratios are almost the same (~2.0 eV; consequently, the absorption edge is not significantly changed. However, the optical band gap corresponding to semiconductor-to-metal phase transition (E2 decreases from 0.53 to 0.18 eV with decreasing O2-Ar ratios.

  12. Migration of O vacancies in α-quartz: The effect of excitons and electron holes

    International Nuclear Information System (INIS)

    Song, Jakyoung; Corrales, L. Rene; Kresse, Georg; Jonsson, Hannes

    2001-01-01

    We have used density-functional theory and the nudged elastic-band method to calculate migration pathways and estimated the activation energy for the diffusion of oxygen vacancies in α-quartz. While the energy barrier for the diffusion of a neutral vacancy is very high, 4.1 eV, the binding of a triplet-state exciton to the vacancy lowers the barrier to 1.7 eV and the attachment of a hole lowers the barrier to 1.9 eV, making the vacancy mobile at commonly used annealing temperatures

  13. Atomic geometry and STM simulations of a TiO.sub.2./sub.(110) surface upon formation of an oxygen vacancy and hydroxyl group

    Czech Academy of Sciences Publication Activity Database

    Mutombo, Pingo; Kiss, A.M.; Berkó, A.; Cháb, Vladimír

    2008-01-01

    Roč. 16, - (2008), 025007/1-025007/9 ISSN 0965-0393 R&D Projects: GA AV ČR IAA1010413 Grant - others:MŠMT(CZ) 9/2004 KONTAKT Institutional research plan: CEZ:AV0Z10100521 Source of funding: V - iné verejné zdroje Keywords : vacance * Oxygen * OH group * STM Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.388, year: 2008

  14. VoIP Security

    OpenAIRE

    Fontanini, Piero

    2008-01-01

    VOIP or Voice Over Internet Protocol is a common term for phone service over IP based networks. There are much information about VoIP and some of how VoIP can be secured. There is however no standard for VoIP and no general solution for VoIP Security. The security in VoIP systems today are often non existing or in best case weak and often based on proprietary solutions. This master thesis investigates threats to VoIP system and describes existing alternatives for securing Vo...

  15. Ionized zinc vacancy mediated ferromagnetism in copper doped ZnO thin films

    Directory of Open Access Journals (Sweden)

    Shi-Yi Zhuo

    2012-03-01

    Full Text Available This paper reports the origin of ferromagnetism in Cu-doped ZnO thin films. Room-temperature ferromagnetism is obtained in all the thin films when deposited at different oxygen partial pressure. An obviously enhanced peak corresponding to zinc vacancy is observed in the photoluminescence spectra, while the electrical spin resonance measurement implies the zinc vacancy is negative charged. After excluding the possibility of direct exchange mechanisms (via free carriers, we tentatively propose a quasi-indirect exchange model (via ionized zinc vacancy for Cu-doped ZnO system.

  16. Wide-range tunable bandgap in Bi1−xCaxFe1−yTiyO3−δ nanoparticles via oxygen vacancy induced structural modulations at room temperature

    International Nuclear Information System (INIS)

    Mocherla, Pavana S V; Sudakar, C; Gautam, Sanjeev; Chae, Keun Hwa; Rao, M S Ramachandra

    2015-01-01

    We demonstrate that oxygen vacancies (V O ) produced by aliovalent (Ca 2+ ) doping in BiFeO 3 (BCFO) and associated structural changes due to V O ordering result in systematic alteration of the bandgap (E g ) over a wide range from 1.5 eV to 2.3 eV. By contrast, the change in the bandgap of a Ca 2+ and Ti 4+ co-doped BiFeO 3 (BCFTO) system, wherein the V O formation is suppressed, is negligible. These contrastive results strongly confirm the role of oxygen vacancies in altering the bandgap of BCFO. Irrespective of doping, microstrain, which is found to be large (0.3 to 1.2%) below a critical size (d c ∼ 60 nm) also produces a small, yet linear change in the bandgap (E g from 2.0 to 2.3 eV). The cubic phase stabilizes gradually in BCFO for x > 0.1 through an orthorhombic phase (for 0.05 < x < 0.1), whereas it directly transforms for x > 0.1 in BCFTO. This change in BCFO at 300 K suggests a high-pressure-like (or high-temperature-like) effect of the oxygen vacancies and dopants on the structure. Systematic variations in the relative intensities and peak positions of Fe d–d transitions in BCFO reveal the local changes in Fe–O–Fe coordination. These results along with XANES and HRTEM studies substantiate the observed structural changes. (paper)

  17. Non-Exercise Estimation of VO[subscript 2]max Using the International Physical Activity Questionnaire

    Science.gov (United States)

    Schembre, Susan M.; Riebe, Deborah A.

    2011-01-01

    Non-exercise equations developed from self-reported physical activity can estimate maximal oxygen uptake (VO[subscript 2]max) as well as sub-maximal exercise testing. The International Physical Activity Questionnaire is the most widely used and validated self-report measure of physical activity. This study aimed to develop and test a VO[subscript…

  18. Low-temperature positron lifetime and Doppler-broadening measurements for single-crystal nickel oxide containing cation vacancies

    International Nuclear Information System (INIS)

    Waber, J.T.; Snead, C.L. Jr.; Lynn, K.G.

    1985-01-01

    Lifetime and Doppler-broadening measurements for positron annihilation in substoichiometric nickelous oxide have been made concomitantly from liquid-helium to room temperature. The concentration of cation vacancies is readily controlled by altering the ambient oxygen pressure while annealing the crystals at 1673 0 K. It was found that neither of the three lifetimes observed or their relative intensities varied significantly with the oxygen pressure, and the bulk rate only increased slightly when the specimen was cooled from room to liquid-helium temperatures. These results are interpreted as indicating that some of the positrons are trapped by the existing cation vacancies and a smaller fraction by vacancy clusters

  19. Securing VoIP keeping your VoIP network safe

    CERN Document Server

    (Bud) Bates, Regis J Jr

    2015-01-01

    Securing VoIP: Keeping Your VoIP Network Safe will show you how to take the initiative to prevent hackers from recording and exploiting your company's secrets. Drawing upon years of practical experience and using numerous examples and case studies, technology guru Bud Bates discusses the business realities that necessitate VoIP system security and the threats to VoIP over both wire and wireless networks. He also provides essential guidance on how to conduct system security audits and how to integrate your existing IT security plan with your VoIP system and security plans, helping you prevent

  20. Room temperature alcohol sensing by oxygen vacancy controlled TiO{sub 2} nanotube array

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, A.; Dutta, K.; Bhowmik, B.; Bhattacharyya, P., E-mail: pb-etc-besu@yahoo.com [Nano-Thin Films and Solid State Gas Sensor Devices Laboratory, Department of Electronics and Telecommunication Engineering, Indian Institute of Engineering Science and Technology (IIEST), Shibpur, Howrah (India); Chattopadhyay, P. P. [Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology (IIEST), Shibpur, Howrah (India)

    2014-08-25

    Oxygen vacancy (OV) controlled TiO{sub 2} nanotubes, having diameters of 50–70 nm and lengths of 200–250 nm, were synthesized by electrochemical anodization in the mixed electrolyte comprising NH{sub 4}F and ethylene glycol with selective H{sub 2}O content. The structural evolution of TiO{sub 2} nanoforms has been studied by field emission scanning electron microscopy. Variation in the formation of OVs with the variation of the structure of TiO{sub 2} nanoforms has been evaluated by photoluminescence and X-ray photoelectron spectroscopy. The sensor characteristics were correlated to the variation of the amount of induced OVs in the nanotubes. The efficient room temperature sensing achieved by the control of OVs of TiO{sub 2} nanotube array has paved the way for developing fast responding alcohol sensor with corresponding response magnitude of 60.2%, 45.3%, and 36.5% towards methanol, ethanol, and 2-propanol, respectively.

  1. Sr{sub 2}MgMoO{sub 6−δ} thin films fabricated using pulsed-laser deposition with high concentrations of oxygen vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Shigematsu, K. [Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Chikamatsu, A., E-mail: chikamatsu@chem.s.u-tokyo.ac.jp; Fukumura, T. [Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); JST-CREST, Bunkyo-ku, Tokyo 113-0033 (Japan); Toyoda, S. [Department of Materials Science and Engineering, Kyoto University, Yoshida-honmachi, Kyoto 606-8501 (Japan); Ikenaga, E. [JASRI/SPring-8, Mikazuki-cho, Hyogo 679-5198 (Japan); Hasegawa, T. [Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); JST-CREST, Bunkyo-ku, Tokyo 113-0033 (Japan); Kanagawa Academy of Science and Technology (KAST), Kawasaki, Kanagawa 213-0012 (Japan)

    2014-06-30

    We fabricated epitaxial thin films of oxygen-vacant Sr{sub 2}MgMoO{sub 6−δ} using pulsed laser deposition. The films showed low resistivity of the order of 10{sup −2} Ω cm at 300 K. X-ray diffraction analyses revealed that Mg and Mo ions in the Sr{sub 2}MgMoO{sub 6−δ} films were considerably disordered, compared to those in bulk Sr{sub 2}MgMoO{sub 6−δ}. The proportion of oxygen vacancies estimated through hard x-ray photoemission measurements was as large as 0.37, and correlated well with the Mg/Mo ordering.

  2. Slow VO2 off-kinetics in skeletal muscle is associated with fast PCr off-kinetics--and inversely.

    Science.gov (United States)

    Korzeniewski, Bernard; Zoladz, Jerzy A

    2013-09-01

    The computer model of the bioenergetic system in skeletal muscle, developed previously, was used to study the effect of the characteristic decay time of the parallel activation of oxidative phosphorylation [τ(OFF)] during muscle recovery on the muscle oxygen consumption rate (Vo2) and phosphocreatine (PCr) work-to-rest transition (off)-kinetics and on the relationship between the Vo2 and PCr rest-to-work transition (on)- and off-kinetics in moderate and heavy exercise. An increase in τ(OFF) slows down the initial phase of the muscle Vo2 off-kinetics and accelerates the PCr off-kinetics. As a result, the relationship between the initial phase of the Vo2 off-kinetics (lasting approximately 3-60 s in computer simulations) and the PCr off-kinetics is inverse: the slower the former, the faster the latter. A faster initial phase of the Vo2 off-kinetics is associated with a slower late phase of the Vo2 off-kinetics, and as a result, the integral of Vo2 above baseline during recovery, representing the oxygen debt, is identical in all cases [values of τ(OFF)] for a given PCr decrease. Depending on τ(OFF), the muscle Vo2 on-kinetics was either equally fast or slower than the Vo2 off-kinetics in moderate exercise and always slower in heavy exercise. PCr on-kinetics was always faster than PCr off-kinetics. This study clearly demonstrates that τ(OFF) has a pronounced impact on the mutual relations between the muscle Vo2 and PCr on- and off-kinetics.

  3. Oxygen vacancies enabled enhancement of catalytic property of Al reduced anatase TiO{sub 2} in the decomposition of high concentration ozone

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Yanhua; Zhang, Xiaolei [Shanghai Institute of Technology, Shanghai 200235 (China); Chen, Li [East China Normal University, Shanghai 200062 (China); Wang, Xiaorui [Shanghai Institute of Technology, Shanghai 200235 (China); Zhang, Na, E-mail: nzhang@sit.edu.cn [Shanghai Institute of Technology, Shanghai 200235 (China); Liu, Yufeng [Shanghai Institute of Technology, Shanghai 200235 (China); Fang, Yongzheng, E-mail: fyz1003@sina.com [Shanghai Institute of Technology, Shanghai 200235 (China)

    2017-06-15

    The catalytic decomposition of gaseous ozone (O{sub 3}) is investigated using anatase TiO{sub 2} (A-TiO{sub 2}) and Aluminum-reduced A-TiO{sub 2} (ARA-TiO{sub 2}) at high concentration and high relative humidity (RH) without light illumination. Compared with the pristine A-TiO{sub 2}, the ARA-TiO{sub 2} sample possesses a unique crystalline core-amorphous shell structure. It is proved to be an excellent solar energy “capture” for solar thermal collectors due to lots of oxygen vacancies. The results indicate that the overall decomposition efficiency of O{sub 3} without any light irradiation has been greatly improved from 4.8% on A-TiO{sub 2} to 100% on ARA-TiO{sub 2} under the RH=100% condition. The ozone conversion over T500/ARA-TiO{sub 2} catalyst is still maintained at 95% after a 72 h test under the reaction condition of 18.5 g/m{sup 3} ozone initial concentration, and RH=90%. The results can be explained that T500/ARA-TiO{sub 2} possesses the largest amorphous contour, the lowest crystallinity, the most surface-active Ti{sup 3+}/T{sup i4+}couples, and the most oxygen vacancies. This result opens a new door to widen the application of TiO{sub 2} in the thermal-catalytic field. - Graphical abstract: The anatase-TiO{sub 2} with various oxidation states and oxygen vacancies have been obtained by aluminum-reduction, and the decomposition efficiency of O{sub 3} has been greatly improved from 4.8% to 100% without irradiation under the RH=100% condition. - Highlights: • The decomposition of gaseous ozone over Al reduced TiO2 (ARA-TiO{sub 2}) is firstly reported. • The decomposition efficiency is up to 100% without any light irradiation on ARA-TiO{sub 2} under RH=100% condition. • The ozone conversion is maintained at 95% after a 72 h test, when C{sub inlet}=18.5 g/m{sup 3} and RH=90%.

  4. Vacancy-induced ferromagnetism in ZnO probed by spin-polarized positron annihilation spectroscopy

    Science.gov (United States)

    Maekawa, Masaki; Abe, Hiroshi; Miyashita, Atsumi; Sakai, Seiji; Yamamoto, Shunya; Kawasuso, Atsuo

    2017-04-01

    We investigated the ferromagnetism of ZnO induced by oxygen implantation by using spin-polarized positron annihilation spectroscopy together with magnetization measurements. The magnetization measurements showed the appearance of ferromagnetism after oxygen implantation and its disappearance during post-implantation annealing at temperatures above 573 K. The Doppler broadening of annihilation radiation (DBAR) spectrum showed asymmetry upon field reversal after oxygen implantation. The obtained differential DBAR spectrum between positive and negative magnetic fields was well-explained with a theoretical calculation considering zinc vacancies. The disappearance of the field-reversal asymmetry of the DBAR spectrum as a result of annealing agreed with the observations of ferromagnetism by magnetization measurements. These results suggest the radiation-induced zinc vacancies to be the source of the observed ferromagnetism of ZnO.

  5. Control of room-temperature defect-mediated ferromagnetism in VO{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Tsung-Han, E-mail: tyang3@ncsu.edu [NSF Center for Advanced Materials and Smart Structures, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907 (United States); Nori, Sudhakar; Mal, Siddhartha; Narayan, Jagdish [NSF Center for Advanced Materials and Smart Structures, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907 (United States)

    2011-09-15

    We report interesting ferromagnetic properties and their control in a vanadium-based oxide system driven by stoichiometric defects. Vanadium oxide (VO{sub 2}) thin films were grown on c-plane sapphire substrates by a pulsed laser deposition technique under different ambient conditions. The ferromagnetism of the epitaxial VO{sub 2} films can be switched on and off by altering the cooling ambient parameters. In addition, the saturated magnetic moments and coercivity of the VO{sub 2} films were found to be a function of the oxygen partial pressure during the growth process. The room-temperature ferromagnetic properties of VO{sub 2} films were correlated with the nature of the microstructure and the growth parameters. The origin of the induced magnetic properties are qualitatively understood to stem from intrinsic structural and stoichiometric defects.

  6. Identification of vacancy defect complexes in transparent semiconducting oxides ZnO, In2O3 and SnO2

    International Nuclear Information System (INIS)

    Makkonen, Ilja; Korhonen, Esa; Prozheeva, Vera; Tuomisto, Filip

    2016-01-01

    Positron annihilation spectroscopy, when combined with supporting high-quality modeling of positron states and annihilation in matter, is a powerful tool for detailed defect identification of vacancy-type defects in semiconductors and oxides. Here we demonstrate that the Doppler broadening of the positron annihilation radiation is a very sensitive means for observing the oxygen environment around cation vacancies, the main open-volume defects trapping positrons in measurements made for transparent semiconducting oxides. Changes in the positron annihilation signal due to external manipulation such as irradiation and annealing can be correlated with the associated changes in the sizes of the detected vacancy clusters. Our examples for ZnO, In 2 O 3 and SnO 2 demonstrate that oxygen vacancies in oxides can be detected directly using positron annihilation spectroscopy when they are complexed with cation vacancies. (paper)

  7. Identification of vacancy defect complexes in transparent semiconducting oxides ZnO, In2O3 and SnO2

    Science.gov (United States)

    Makkonen, Ilja; Korhonen, Esa; Prozheeva, Vera; Tuomisto, Filip

    2016-06-01

    Positron annihilation spectroscopy, when combined with supporting high-quality modeling of positron states and annihilation in matter, is a powerful tool for detailed defect identification of vacancy-type defects in semiconductors and oxides. Here we demonstrate that the Doppler broadening of the positron annihilation radiation is a very sensitive means for observing the oxygen environment around cation vacancies, the main open-volume defects trapping positrons in measurements made for transparent semiconducting oxides. Changes in the positron annihilation signal due to external manipulation such as irradiation and annealing can be correlated with the associated changes in the sizes of the detected vacancy clusters. Our examples for ZnO, In2O3 and SnO2 demonstrate that oxygen vacancies in oxides can be detected directly using positron annihilation spectroscopy when they are complexed with cation vacancies.

  8. Efficient carbon dots/NiFe-layered double hydroxide/BiVO4 photoanodes for photoelectrochemical water splitting

    Science.gov (United States)

    Lv, Xiaowei; Xiao, Xin; Cao, Minglei; Bu, Yi; Wang, Chuanqing; Wang, Mingkui; Shen, Yan

    2018-05-01

    Modification of semiconductor photoanodes with oxygen evolution catalyst (OEC) is an effective approach for improving photoelectrochemical (PEC) water splitting efficiency. In the configuration, how to increase the activity of OEC is crucial to further improve PEC performance. Herein, a ternary photoanode system was designed to enhance PEC efficiency of photoelectrodes through introducing carbon dots (CDs), NiFe-layered double hydroxide (NiFe-LDH) nanosheets on BiVO4 particles. Systematic research shows that NiFe-LDH serves as an OEC which accelerates oxygen evolution kinetics, while the introduction of CDs can further reduce charge transfer resistance and overpotential for oxygen evolution. Under the synergistic effect of NiFe-LDH and CDs, the photocurrent and incident photon to current conversion efficiency (IPCE) of the resulting CDs/NiFe-LDH/BiVO4 photoanode is improved significantly than those of the NiFe-LDH/BiVO4 electrode. Consequently, such a ternary heterostructure could be an alternative way to further enhance PEC water splitting performance.

  9. VO2(B conversion to VO2(A and VO2(M and their oxidation resistance and optical switching properties

    Directory of Open Access Journals (Sweden)

    Zhang Yifu

    2016-03-01

    Full Text Available Vanadium dioxide VO2 has been paid in recent years increasing attention because of its various applications, however, its oxidation resistance properties in air atmosphere have rarely been reported. Herein, VO2(B nanobelts were transformed into VO2(A and VO2(M nanobelts by hydrothermal route and calcination treatment, respectively. Then, we comparatively studied the oxidation resistance properties of VO2(B, VO2(A and VO2(M nanobelts in air atmosphere by thermo-gravimetric analysis and differential thermal analysis (TGA/DTA. It was found that the nanobelts had good thermal stability and oxidation resistance below 341 °C, 408 °C and 465 °C in air, respectively, indicating that they were stable in air at room temperature. The fierce oxidation of the nanobelts occurred at 426, 507 and 645 °C, respectively. The results showed that the VO2(M nanobelts had the best thermal stability and oxidation resistance among the others. Furthermore, the phase transition temperatures and optical switching properties of VO2(A and VO2(M were studied by differential scanning calorimetry (DSC and variable temperature infrared spectra. It was found that the VO2(A and VO2(M nanobelts had outstanding thermochromic character and optical switching properties.

  10. Synthesis and oxygen vacancy related NO{sub 2} gas sensing properties of ZnO:Co nanorods arrays gown by a hydrothermal method

    Energy Technology Data Exchange (ETDEWEB)

    Zou, Changwei, E-mail: qingyihaiyanas@163.com; Liang, Feng; Xue, Shuwen

    2015-10-30

    Highlights: • Co doped ZnO:Co nanorods were grown by hydrothermal method. • The NO{sub 2} response reaches a maximum value of 88 at 210 °C. • The stability of NO{sub 2} on ZnO is enhanced with the presence of V{sub O}. - Abstract: Highly ordered Co doped ZnO:Co nanorods arrays with Co concentrations of 1.6, 1.9 and 3.1 at% were uniformly grown on FTO glass substrate by hydrothermal method. The X-ray diffraction patterns of the undoped and Co doped ZnO nanorods revealed characteristic peaks of (1 0 0), (0 0 2), (1 0 1), (1 0 3) and (1 1 2), corresponding to the hexagonal wurtzite phase of ZnO. For ZnO:Co nanorods with Co concentrations of 3.1 at%, the NO{sub 2} response reached a maximum value of 88 at temperature of 210 °C. However, the response of ZnO:Co nanorods with Co concentrations of 3.1 at% decreased from 82 to 29 with the increasing of O{sub 2} annealing temperature from 0 to 700 °C. As confirmed by the XPS, PL, Raman and I–V results, the oxygen vacancies and electron concentrations were the dominating effects and an oxygen vacancy mediated NO{sub 2} sensing mechanism was presented and discussed.

  11. Enhanced photocatalytic performance of BiVO_4 in aqueous AgNO_3 solution under visible light irradiation

    International Nuclear Information System (INIS)

    Huang, Chien-Kai; Wu, Tsunghsueh; Huang, Chang-Wei; Lai, Chi-Yung; Wu, Mei-Yao; Lin, Yang-Wei

    2017-01-01

    Graphical abstract: Ag"+ ions enhanced photocatalytic activity of BiVO_4 under visible light irradiation. - Highlights: • The presence of Ag"+ ions enhanced the photodegradation activity of BiVO_4. • Photoreduction of Ag deposited on the BiVO_4 surface was obtained. • Luminescence and electrochemical results elucidated the photocatalytic mechanism. • Holes and oxygen radicals were the main reactive species generated by BiVO_4/Ag"+. • Used BiVO_4/Ag"+ exhibited photocatalytic antibacterial activity toward E. coli. - Abstract: Monoclinic-phase bismuth vanadate (BiVO_4) with a 2.468 eV band gap exhibited enhanced synergic photodegradation activity toward methylene blue (MB) when combined with silver ions (Ag"+) in an aqueous solution under visible light irradiation. The mass ratio of AgNO_3 to BiVO_4 and the calcination temperature were discovered to considerably affect the degradation activity of BiVO_4/Ag"+. Superior photocatalytic performance was obtained when BiVO_4 was mixed with 0.01%(w/v) AgNO_3 solution, and complete degradation of MB was achieved after 25 min visible light irradiation, outperforming BiVO_4 or AgNO_3 solution alone. The enhanced photodegradation was investigated using systematic luminescence measurements, electrochemical impedance spectroscopy, and scavenger addition, after which a photocatalytic mechanism for MB degradation under visible light irradiation was identified that involved oxygen radicals and holes. This study also discovered the two dominating processes involved in enhancing the electron–hole separation efficiency and reducing their recombination rate, namely photoreduction of Ag"+ and the formation of a BiVO_4/Ag heterojunction. The synergic effect between BiVO_4 and Ag"+ was discovered to be unique. BiVO_4/Ag"+ was successfully used to degrade two other dyes and disinfect Escherichia Coli. A unique fluorescent technique using BiVO_4 and a R6G solution to detect Ag"+ ions in water was discovered.

  12. Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO{sub 3} interface: Control of oxygen vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Kormondy, Kristy J.; Posadas, Agham B.; Demkov, Alexander A., E-mail: demkov@physics.utexas.edu [Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States); Ngo, Thong Q.; Ekerdt, John G. [Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Lu, Sirong; Smith, David J.; McCartney, Martha R. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Goble, Nicholas; Gao, Xuan P. A. [Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106 (United States); Jordan-Sweet, Jean [IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 (United States)

    2015-03-07

    In this paper, we report on the highly conductive layer formed at the crystalline γ-alumina/SrTiO{sub 3} interface, which is attributed to oxygen vacancies. We describe the structure of thin γ-alumina layers deposited by molecular beam epitaxy on SrTiO{sub 3} (001) at growth temperatures in the range of 400–800 °C, as determined by reflection-high-energy electron diffraction, x-ray diffraction, and high-resolution electron microscopy. In situ x-ray photoelectron spectroscopy was used to confirm the presence of the oxygen-deficient layer. Electrical characterization indicates sheet carrier densities of ∼10{sup 13 }cm{sup −2} at room temperature for the sample deposited at 700 °C, with a maximum electron Hall mobility of 3100 cm{sup 2}V{sup −1}s{sup −1} at 3.2 K and room temperature mobility of 22 cm{sup 2}V{sup −1}s{sup −1}. Annealing in oxygen is found to reduce the carrier density and turn a conductive sample into an insulator.

  13. Zinc Vacancy Formation and its Effect on the Conductivity of ZnO

    Science.gov (United States)

    Khan, Enamul; Weber, Marc; Langford, Steve; Dickinson, Tom

    2010-03-01

    Exposing single crystal ZnO to 193-nm ArF excimer laser radiation can produce metallic zinc nanoparticles along the surface. The particle production mechanism appears to involve interstitial-vacancy pair formation in the near-surface bulk. Conductivity measurements made with one probe inside the laser spot and the other outside show evidence for rectifying behavior. Positron annihilation spectroscopy confirms the presence of Zn vacancies. We suggest that Zn vacancies are a possible source of p-type behavior in irradiated ZnO. Quadrupole mass spectroscopy shows that both oxygen and zinc are emitted during irradiation. Electron-hole pair production has previously been invoked to account for particle desorption from ZnO during UV illumination. Our results suggest that preexisting and laser-generated defects play a critical role in particle desorption and Zn vacancy formation.

  14. Vacancy defects in epitaxial La0.7Sr0.3MnO3 thin films probed by a slow positron beam

    International Nuclear Information System (INIS)

    Jin, S W; Zhou, X Y; Wu, W B; Zhu, C F; Weng, H M; Wang, H Y; Zhang, X F; Ye, B J; Han, R D

    2004-01-01

    Vacancy defects in epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO) thin films on LaAlO 3 substrates were detected using a variable energy positron beam. The line-shape S parameter of the epitaxial thin films deposited at different oxygen pressures was measured as a function of the implanting positron energy E. Our results show that the S parameter of the films changes non-monotonically with their deposition oxygen pressures. For the films deposited at lower oxygen pressures, the increase in S value in the films is attributed to the increase in oxygen vacancies and/or related defect-V O complexes, and for those deposited at higher oxygen pressures, the larger S parameter of the films is caused by the grain boundaries and/or metallic ion vacancies. The surface morphology of the films was also characterized to analyse the open volume defects in the LSMO films

  15. Towards understanding the electronic structure of Fe-doped CeO2 nanoparticles with X-ray spectroscopy.

    Science.gov (United States)

    Wang, Wei-Cheng; Chen, Shih-Yun; Glans, Per-Anders; Guo, Jinghua; Chen, Ren-Jie; Fong, Kang-Wei; Chen, Chi-Liang; Gloter, Alexandre; Chang, Ching-Lin; Chan, Ting-Shan; Chen, Jin-Ming; Lee, Jyh-Fu; Dong, Chung-Li

    2013-09-21

    This study reports on the electronic structure of Fe-doped CeO2 nanoparticles (NPs), determined by coupled X-ray absorption spectroscopy and X-ray emission spectroscopy. A comparison of the local electronic structure around the Ce site with that around the Fe site indicates that the Fe substitutes for the Ce. The oxygen K-edge spectra that originated from the hybridization between cerium 4f and oxygen 2p states are sensitive to the oxidation state and depend strongly on the concentration of Fe doping. The Ce M(4,5)-edges and the Fe L(2,3)-edges reveal the variations of the charge states of Ce and Fe upon doping, respectively. The band gap is further obtained from the combined absorption-emission spectrum and decreased upon Fe doping, implying Fe doping introduces vacancies. The oxygen vacancies are induced by Fe doping and the spectrum reveals the charge transfer between Fe and Ce. Fe(3+) doping has two major effects on the formation of ferromagnetism in CeO2 nanoparticles. The first, at an Fe content of below 5%, is that the formation of Fe(3+)-Vo-Ce(3+) introduces oxygen deficiencies favoring ferromagnetism. The other, at an Fe content of over 5%, is the formation of Fe(3+)-Vo-Fe(3+), which favors antiferromagnetism, reducing the Ms. The defect structures Fe(3+)-Vo-Ce(3+) and Fe(3+)-Vo-Fe(3+) are crucial to the magnetism in these NPs and the change in Ms can be described as the effect of competitive interactions of magnetic polarons and paired ions.

  16. Doping strategies to control A-centres in silicon: Insights from hybrid density functional theory

    KAUST Repository

    Wang, Hao; Chroneos, Alexander I.; Londos, Charalampos A.; Sgourou, Efstratia N.; Schwingenschlö gl, Udo

    2014-01-01

    Hybrid density functional theory is used to gain insights into the interaction of intrinsic vacancies (V) and oxygen-vacancy pairs (VO, known as A-centres) with the dopants (D) germanium (Ge), tin (Sn), and lead (Pb) in silicon (Si). We determine the structures as well as binding and formation energies of the DVO and DV complexes. The results are discussed in terms of the density of states and in view of the potential of isovalent doping to control A-centres in Si. We argue that doping with Sn is the most efficient isovalent doping strategy to suppress A-centres by the formation of SnVO complexes, as these are charge neutral and strongly bound. © 2014 the Owner Societies.

  17. An oxygen-vacancy-rich Z-scheme g-C3N4/Pd/TiO2 heterostructure for enhanced visible light photocatalytic performance

    Science.gov (United States)

    Guo, Yanru; Xiao, Limin; Zhang, Min; Li, Qiuye; Yang, Jianjun

    2018-05-01

    An oxygen-vacancy-rich Z-scheme g-C3N4/Pd/TiO2 ternary nanocomposite was fabricated using nanotubular titanic acid as precursors via a simple photo-deposition of Pd nanoparticles and calcination process. The prepared nanocomposites were investigated by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-visible diffuse reflectance spectroscopy, respectively. For g-C3N4/TiO2 binary nanocomposites, at the optimal content of g-C3N4 (2%), the apparent photocatalytic activity of 2%g-C3N4/TiO2 was 9 times higher than that of pure TiO2 under visible-light illumination. After deposition of Pd (1 wt%) at the contact interface between g-C3N4 and TiO2, the 2%g-C3N4/Pd/TiO2 ternary nanocomposites demonstrated the highest visible-light-driven photocatalytic activity for the degradation of gaseous propylene, which was 16- and 2-fold higher activities than pure TiO2 and 2%g-C3N4/TiO2, respectively. The mechanism for the enhanced photocatalytic performance of the g-C3N4/Pd/TiO2 photo-catalyst is proposed to be based on the efficient separation of photo-generated electron-hole pairs through Z-scheme system, in which uniform dispersity of Pd nanoparticles at contact interface between g-C3N4 and TiO2 and oxygen vacancies promote charge separation.

  18. Effect of oxygen vacancy and dopant concentration on the magnetic properties of high spin Co2+ doped TiO2 nanoparticles

    International Nuclear Information System (INIS)

    Choudhury, B.; Choudhury, A.; Maidul Islam, A.K.M.; Alagarsamy, P.; Mukherjee, M.

    2011-01-01

    Co doped TiO 2 nanoparticles have been synthesized by a simple sol-gel route taking 7.5, 9.5 and 10.5 mol% of cobalt concentration. Formation of nanoparticles is confirmed by XRD and TEM. Increase in d-spacing occurs for (0 0 4) and (2 0 0) peak with increase in impurity content. Valence states of Co and its presence in the doped material is confirmed by XPS and EDX. The entire vacuum annealed samples show weak ferromagnetism. Increased magnetization is found for 9.5 mol% but this value again decreases for 10.5 mol% due to antiferromagnetic interactions. A blocking temperature of 37.9 K is obtained, which shows shifting to high temperature as the dopant concentration is increased. The air annealed sample shows only paramagnetic behavior. Temperature dependent magnetic measurements for the air annealed sample shows antiferromagnetic behavior with a Curie-Weiss temperature of -16 K. Here we report that oxygen vacancy and cobalt aggregates are a key factor for inducing ferromagnetism-superparamagnetism in the vacuum annealed sample. Appearance of negative Curie-Weiss temperature reveals the presence of antiferromagnetic Co 3 O 4 , which is the oxidation result of metallic Co or cobalt clusters present on the host TiO 2 . - Research highlights: → Oxygen vacancy induces ferromagnetism in cobalt doped anatase TiO2 nanoparticles. → On air annealing the sample loses ferromagnetism giving rise to paramagnetism. → Saturation magnetization decreases at higher doping concentration. → Blocking of magnetic moment occurs due to the presence of cobalt clusters.

  19. Vacancy-type defects induced by grinding of Si wafers studied by monoenergetic positron beams

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Yoshihara, Nakaaki [Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Mizushima, Yoriko [Devices and Materials Labs Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197 (Japan); ICE Cube Center, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Kim, Youngsuk [ICE Cube Center, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Disco Corporation, Ota, Tokyo 143-8580 (Japan); Nakamura, Tomoji [Devices and Materials Labs Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197 (Japan); Ohba, Takayuki [ICE Cube Center, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Oshima, Nagayasu; Suzuki, Ryoichi [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568 (Japan)

    2014-10-07

    Vacancy-type defects introduced by the grinding of Czochralski-grown Si wafers were studied using monoenergetic positron beams. Measurements of Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons showed that vacancy-type defects were introduced in the surface region (<98 nm), and the major defect species were identified as (i) relatively small vacancies incorporated in dislocations and (ii) large vacancy clusters. Annealing experiments showed that the defect concentration decreased with increasing annealing temperature in the range between 100 and 500°C. After 600–700°C annealing, the defect-rich region expanded up to about 170 nm, which was attributed to rearrangements of dislocation networks, and a resultant emission of point defects toward the inside of the sample. Above 800°C, the stability limit of those vacancies was reached and they started to disappear. After the vacancies were annealed out (900°C), oxygen-related defects were the major point defects and they were located at <25 nm.

  20. Effects of daily activity recorded by pedometer on peak oxygen consumption (VO2peak), ventilatory threshold and leg extension power in 30- to 69-year-old Japanese without exercise habit.

    Science.gov (United States)

    Zhang, Jian-Guo; Ohta, Toshiki; Ishikawa-Takata, Kazuko; Tabata, Izumi; Miyashita, Mitsumasa

    2003-09-01

    The relationships among walk steps, exercise habits and peak oxygen consumption (VO2peak), ventilatory threshold (VT) and leg extension power (LEP) were examined in 709 apparently healthy Japanese subjects (male 372, female 337) aged 30-69 years. Walk steps were evaluated using a pedometer. VO2peak and VT were assessed by a cycle ergometer test, while LEP was measured with an isokinetic leg extension system (Combi, Anaero Press 3500, Japan). Subjects who participated in exercise three times or more a week demonstrated significantly greater VO2peak and VT when compared with subjects without exercise habits. When a separate analysis was conducted on subjects who exercised fewer than three times per week, we found that the subgroup with the highest number of walk steps showed significantly greater VT in all male subjects and female subjects aged 30-49 years, but a significantly greater VO2peak only in females aged 30-49 years, when compared to the subgroup with the fewest walk steps. These results suggest that although some people exercise less than three times a week, if they are quite active in daily life, such activities might also confer benefits upon their fitness.

  1. Radiation-induced defects in Czochralski-grown silicon containing carbon and germanium

    International Nuclear Information System (INIS)

    Londos, C A; Andrianakis, A; Emtsev, V V; Ohyama, H

    2009-01-01

    Formation processes of vacancy-oxygen (VO) and carbon interstitial-oxygen interstitial (C i O i ) complexes in electron-irradiated Czochralski-grown Si crystals (Cz–Si), also doped with Ge, are investigated. IR spectroscopy measurements are employed to monitor the production of these defects. In Cz–Si with carbon concentrations [C s ] up to 1 × 10 17 cm −3 and Ge concentrations [Ge] up to 1 × 10 20 cm −3 the production rate of VO defects as well as the rate of oxygen loss show a slight growth of about 10% with the increasing Ge concentration. At high concentrations of carbon [C s ] around 2 × 10 17 cm −3 the production rate of VO defects is getting larger by ∼40% in Cz–Si:Ge at Ge concentrations around 1 × 10 19 cm −3 and then at [Ge] ≈ 2 × 10 20 cm −3 this enlargement drops to ∼13%, thus approaching the values characteristic of lesser concentrations of carbon. A similar behavior against Ge concentration displays the production rate of C i O i complexes. The same trend is also observed for the rate of carbon loss, whereas the trend for the rate of oxygen loss is opposite. The behavior of Ge atoms is different at low and high concentrations of this isoelectronic impurity in Cz–Si. At low concentrations most isolated Ge atoms serve as temporary traps for vacancies preventing them from indirect annihilation with self-interstitials. At high concentrations Ge atoms are prone to form clusters. The latter ones are traps for vacancies and self-interstitials due to the strain fields, increasing the importance of indirect annihilation of intrinsic point defects. Such a model allows one to give a plausible explanation for the obtained results. A new band at 994 cm −1 seen only in irradiated Ge-doped Cz–Si is also studied. Interestingly, its annealing behavior was found to be very similar to that of VO complexes

  2. Mobility-electron density relation probed via controlled oxygen vacancy doping in epitaxial BaSnO3

    Directory of Open Access Journals (Sweden)

    Koustav Ganguly

    2017-05-01

    Full Text Available The recently discovered high room temperature mobility in wide band gap semiconducting BaSnO3 is of exceptional interest for perovskite oxide heterostructures. Critical open issues with epitaxial films include determination of the optimal dopant and understanding the mobility-electron density (μ-n relation. These are addressed here through a transport study of BaSnO3(001 films with oxygen vacancy doping controlled via variable temperature vacuum annealing. Room temperature n can be tuned from 5 × 1019 cm−3 to as low as 2 × 1017 cm−3, which is shown to drive a weak- to strong-localization transition, a 104-fold increase in resistivity, and a factor of 28 change in μ. The data reveal μ ∝ n0.65 scaling over the entire n range probed, important information for understanding mobility-limiting scattering mechanisms.

  3. Positron annihilation study of vacancy-type defects in fast-neutron-irradiated MgO·nAl2O3

    International Nuclear Information System (INIS)

    Rahman, Abu Zayed Mohammad Saliqur; Li, Zhuoxin; Cao, Xingzhong; Wang, Baoyi; Wei, Long; Xu, Qiu; Atobe, Kozo

    2014-01-01

    Highlights: •Detection of Al monovacancy by positron lifetime spectroscopy in fast neutron-irradiated MgO·nAl 2 O 3 (n=2). •Concentration of defects is also estimated for Al monovacancy. •O atom peak was observed by using coincidence Doppler broadening spectroscopy. -- Abstract: The positron lifetimes of fast-neutron-irradiated MgO·nAl 2 O 3 single crystals were measured to investigate the formation of cation vacancies. Al monovacancy was possibly observed in samples irradiated by fast neutrons at ultra-low temperatures. Additionally, vacancy-oxygen complex centers were possibly observed in samples irradiated at higher temperatures and fast neutron fluences. Coincidence Doppler broadening (CDB) spectra were measured to obtain information regarding the vicinity of vacancy-type defects. A peak at approximately 11 × 10 −3 m 0 c was observed, which may be due to the presence of oxygen atoms in the neighborhood of the vacancies

  4. Enhanced photocatalytic performance of BiVO{sub 4} in aqueous AgNO{sub 3} solution under visible light irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Chien-Kai [Department of Chemistry, National Changhua University of Education, Changhua City, Taiwan (China); Wu, Tsunghsueh [Department of Chemistry, University of Wisconsin-Platteville, Platteville (United States); Huang, Chang-Wei [Department of Chemistry, National Changhua University of Education, Changhua City, Taiwan (China); Lai, Chi-Yung [Department of Biology, National Changhua University of Education, Changhua, Taiwan (China); Wu, Mei-Yao, E-mail: meiyaowu0919@gmail.com [Research Centre for Traditional Chinese Medicine, Department of Medical Research, China Medical University Hospital, Taichung City, Taiwan (China); Lin, Yang-Wei, E-mail: linywjerry@cc.ncue.edu.tw [Department of Chemistry, National Changhua University of Education, Changhua City, Taiwan (China)

    2017-03-31

    Graphical abstract: Ag{sup +} ions enhanced photocatalytic activity of BiVO{sub 4} under visible light irradiation. - Highlights: • The presence of Ag{sup +} ions enhanced the photodegradation activity of BiVO{sub 4}. • Photoreduction of Ag deposited on the BiVO{sub 4} surface was obtained. • Luminescence and electrochemical results elucidated the photocatalytic mechanism. • Holes and oxygen radicals were the main reactive species generated by BiVO{sub 4}/Ag{sup +}. • Used BiVO{sub 4}/Ag{sup +} exhibited photocatalytic antibacterial activity toward E. coli. - Abstract: Monoclinic-phase bismuth vanadate (BiVO{sub 4}) with a 2.468 eV band gap exhibited enhanced synergic photodegradation activity toward methylene blue (MB) when combined with silver ions (Ag{sup +}) in an aqueous solution under visible light irradiation. The mass ratio of AgNO{sub 3} to BiVO{sub 4} and the calcination temperature were discovered to considerably affect the degradation activity of BiVO{sub 4}/Ag{sup +}. Superior photocatalytic performance was obtained when BiVO{sub 4} was mixed with 0.01%(w/v) AgNO{sub 3} solution, and complete degradation of MB was achieved after 25 min visible light irradiation, outperforming BiVO{sub 4} or AgNO{sub 3} solution alone. The enhanced photodegradation was investigated using systematic luminescence measurements, electrochemical impedance spectroscopy, and scavenger addition, after which a photocatalytic mechanism for MB degradation under visible light irradiation was identified that involved oxygen radicals and holes. This study also discovered the two dominating processes involved in enhancing the electron–hole separation efficiency and reducing their recombination rate, namely photoreduction of Ag{sup +} and the formation of a BiVO{sub 4}/Ag heterojunction. The synergic effect between BiVO{sub 4} and Ag{sup +} was discovered to be unique. BiVO{sub 4}/Ag{sup +} was successfully used to degrade two other dyes and disinfect Escherichia Coli. A

  5. Vaporization study on vanadium-oxygen solid solution by mass spectrometric method

    International Nuclear Information System (INIS)

    Banchorndhevakul, W.; Matsui, Tsuneo; Naito, Keiji

    1986-01-01

    The vapor pressures over vanadium-oxygen solid solution (0.001 ≤ O/V ≤ 0.145) were measured by mass-spectrometric method in the temperature range of 1,855 ∼ 2,117 K. The main vapor species were observed to be V(g) and VO(g). The vapor pressure of V(g) is higher than that of VO(g) over the solid solutions with all O/V ratios except for O/V = 0.145. The vapor pressure of V(g) is nearly independent of O/V ratio. The vapor pressure of VO(g) decreases with decreasing O/V ratio. The oxygen partial pressure was calculated as a function of temperature and O/V ratio from the vapor pressures of V(g) and VO(g), from which the partial molar enthalpy and entropy of oxygen in the solid solution were determined. The partial molar enthalpy of oxygen was observed to be independent of composition, suggesting the presence of very weak interaction between interstitial oxygens. The compositional dependence of the partial molar entropy of oxygen can be explained by assuming the occupation of the octahedral site in bcc vanadium lattice by the interstitial oxygens. The excess partial molar entropy of oxygen was compared with the value derived from the sum of the contributions from the volume expansion, electronic heat capacity and vibrational terms. (author)

  6. Interaction of nitrogen with vacancy defects in N+-implanted ZnO studied using a slow positron beam

    International Nuclear Information System (INIS)

    Chen, Z.Q.; Maekawa, M.; Kawasuso, A.; Suzuki, R.; Ohdaira, T.

    2005-01-01

    ZnO crystals were implanted with N + , O + , and Al + , and co-implanted with O + /N + and Al + /N + ions. Positron annihilation measurements indicate introduction of vacancy clusters upon implantation. In the N + -implanted and Al + /N + co-implanted samples, these vacancy clusters are only partially annealed at 800 deg. C, as compared with their entire recovery in the O + - and Al + -implanted samples at 800-900 deg. C, suggesting a strong interaction between nitrogen and vacancy clusters. However, in the O + /N + co-implanted sample, most vacancy clusters disappear at 800 deg. C. Probably oxygen scavenges nitrogen to enhance the annealing of the vacancy clusters. Upon further annealing at 1000-1100 deg. C, nitrogen also forms stable complexes with thermally generated vacancies. These nitrogen-related vacancy complexes need high-temperature annealing at 1200-1250 deg. C to be fully removed

  7. Adsorption and magnetism of bilayer graphene on the MnO polar surface with oxygen vacancies in the interface: First principles study

    Science.gov (United States)

    Ilyasov, Victor V.; Ershov, Igor V.; Popova, Inna G.; Pham, Khang D.; Nguyen, Chuong V.

    2018-05-01

    In this paper, we investigate systematically the structural, electronic, magnetic and adsorption properties of Bernal-stacked bilayer graphene on MnO(111) surface terminated by an oxygen atom, as a function of nonstoichiometric composition of the BLG/MnOx(111) interface. For additional functionalization of the BLG/MnOx(111) system, we also studied the adsorption properties of oxygen adsorbed on the BLG/MnOx(111) interface. Our results showed that the BLG is bound to the MnOx(111) substrate by the weak interaction for both spin-up and spin-down. Furthermore, we found that BLG adsorbed on the MnOx(111) substrate with a reduced oxygen symmetry in the interface is accompanied with a downshift of the Fermi level, which identifies the band structure of BLG as a p-type semiconductor. Upon interaction between BLG and MnOx(111) substrate, a forbidden gap of about 350 meV was opened between its bonding and antibonding π bands. A forbidden gap and the local magnetic moments in bilayer graphene can be controlled by changing the oxygen nonstoichometry or by oxygen adsorption. Additionally, magnetism has been predicted in the bilayer graphene adsorbed on the polar MnOx(111) surface with oxygen vacancies in the BLG/MnOx(111) interface, and its nature has also been discussed in this work. These results showed that the adsorption of bilayer graphene on the MnO(111) substrate can be used for developing novel generation of electronic and spintronic devices.

  8. Estimates of point defect production in α-quartz using molecular dynamics simulations

    Science.gov (United States)

    Cowen, Benjamin J.; El-Genk, Mohamed S.

    2017-07-01

    Molecular dynamics (MD) simulations are performed to investigate the production of point defects in α-quartz by oxygen and silicon primary knock-on atoms (PKAs) of 0.25-2 keV. The Wigner-Seitz (WS) defect analysis is used to identify the produced vacancies, interstitials, and antisites, and the coordination defect analysis is used to identify the under and over-coordinated oxygen and silicon atoms. The defects at the end of the ballistic phase and the residual defects, after annealing, increase with increased PKA energy, and are statistically the same for the oxygen and silicon PKAs. The WS defect analysis results show that the numbers of the oxygen vacancies and interstitials (VO, Oi) at the end of the ballistic phase is the highest, followed closely by those of the silicon vacancies and interstitials (VSi, Sii). The number of the residual oxygen and silicon vacancies and interstitials are statistically the same. In addition, the under-coordinated OI and SiIII, which are the primary defects during the ballistic phase, have high annealing efficiencies (>89%). The over-coordinated defects of OIII and SiV, which are not nearly as abundant in the ballistic phase, have much lower annealing efficiencies (PKA energy.

  9. Selective formation of VO2(A) or VO2(R) polymorph by controlling the hydrothermal pressure

    International Nuclear Information System (INIS)

    Ji Shidong; Zhang Feng; Jin Ping

    2011-01-01

    Missing VO 2 (A) usually occurs during the preparation of VO 2 polymorphs. This leads to an ambiguous understanding of the transformation between VO 2 polymorphs. The calculation of the ground state energies for different VO 2 polymorphs indicated that there is only a small energy gap between VO 2 (A) and VO 2 (R), which destined that the transformation from VO 2 (A) to VO 2 (R) should be pressure sensitive. This hypothesis was verified during the synthesizing of VO 2 polymorphs by reducing V 2 O 5 with oxalic acid through hydrothermal treatment process. Selective formation of pure phase VO 2 (A) or VO 2 (R) was achieved by controlling the hydrothermal pressure through varying the filling ratio at 270 deg. C. It was found that a filling ratio over 0.5 favors the formation of pure VO 2 (R) while a reduced filling ratio to 0.4 or lower results in the formation of VO 2 (A). Based on our experiments, VO 2 (B) nanobelts were always first formed and then it transformed to VO 2 (A) by assembling process at increased temperature or extended reaction time. Under further higher pressure, the VO 2 (A) transformed spontaneously to VO 2 (R) initialized from the volume shrinkage due to the formation of denser VO 2 (R). - Graphical abstract: Selective formation of VO 2 (A) or VO 2 (R) could be achieved by controlling the system pressure through varying the filling ratio during hydrothermal treatment. Highlights: → Selective formation of VO 2 polymorphs by controlling hydrothermal pressure. → Ground state energy characteristics were revealed for the first time. → Phase transformation mechanism was clearly elucidated.

  10. Benign Synthesis of Black Microspheres of Anatase TiO2 with Paramagnetic Oxygen Vacancies through NH3 Treatment.

    Science.gov (United States)

    Maqbool, Qysar; Srivastava, Aasheesh

    2017-10-09

    Coloured TiO 2 is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres (B-TiO 2 ) through a two-step process is reported. In the first step, amorphous white TiO 2 microspheres (W-TiO 2 ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W-TiO 2 is thermally annealed at 500 °C to obtain B-TiO 2 . The diffuse reflectance analysis showed that B-TiO 2 absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B-TiO 2 that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single-electron-trapped (or paramagnetic) oxygen vacancies (V o ⋅) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Sc and Nb Dopants in SrCoO3 Modulate Electronic and Vacancy Structures for Improved Water Splitting and SOFC Cathodes

    KAUST Repository

    Tahini, Hassan A.; Tan, Xin; Zhou, Wei; Zhu, Zhonghua; Schwingenschlö gl, Udo; Smith, Sean C.

    2017-01-01

    SrCoO3 is a promising material in the field of electrocatalysis. Difficulties in synthesising the material in its cubic phase have been overcome by doping it with Sc and Nb ions [Mater. Horiz.2015, 2, 495–501]. Using ab initio calculations and special quasi random structures we undertake a systematic study of these dopants in order to elucidate the effect of doping on electronic structure of the SrCoO3 host and the formation of oxygen vacancies. We find that while the overall electronic structure of SrCoO3 is preserved, increasing the Sc fraction leads to a decrease of electrical conductivity, in agreement with earlier experimental work. For low Sc and Nb doping fractions we find that the oxygen vacancy formation increases relative to undoped SrCoO3. However, as the dopants concentration is increased the vacancy formation energy drops significantly, indicating a strong tendency to accommodate high concentration of oxygen vacancies and hence non-stoichiometry. This is explained based on the electronic instabilities caused by the presence of Sc ions which weakens the B-O interactions as well as the increased degree of electron delocalization on the oxygen sublattice. Sc dopants also shift the p-band centre closer to the Fermi level, which can be associated with experimentally reported improvements in oxygen evolution reactions. These findings provide crucial baseline information for the design of better electrocatalysts for oxygen evolution reactions as well as fuel-cell cathode materials.

  12. Sc and Nb Dopants in SrCoO3 Modulate Electronic and Vacancy Structures for Improved Water Splitting and SOFC Cathodes

    KAUST Repository

    Tahini, Hassan A.

    2017-01-12

    SrCoO3 is a promising material in the field of electrocatalysis. Difficulties in synthesising the material in its cubic phase have been overcome by doping it with Sc and Nb ions [Mater. Horiz.2015, 2, 495–501]. Using ab initio calculations and special quasi random structures we undertake a systematic study of these dopants in order to elucidate the effect of doping on electronic structure of the SrCoO3 host and the formation of oxygen vacancies. We find that while the overall electronic structure of SrCoO3 is preserved, increasing the Sc fraction leads to a decrease of electrical conductivity, in agreement with earlier experimental work. For low Sc and Nb doping fractions we find that the oxygen vacancy formation increases relative to undoped SrCoO3. However, as the dopants concentration is increased the vacancy formation energy drops significantly, indicating a strong tendency to accommodate high concentration of oxygen vacancies and hence non-stoichiometry. This is explained based on the electronic instabilities caused by the presence of Sc ions which weakens the B-O interactions as well as the increased degree of electron delocalization on the oxygen sublattice. Sc dopants also shift the p-band centre closer to the Fermi level, which can be associated with experimentally reported improvements in oxygen evolution reactions. These findings provide crucial baseline information for the design of better electrocatalysts for oxygen evolution reactions as well as fuel-cell cathode materials.

  13. Effects of oxygen delivery, dietary nitrate, intensified training and prior exercise on oxygen uptake kinetics and performance in humans

    DEFF Research Database (Denmark)

    Christensen, Peter Møller

    benefits from supplementing with nitrate to improve exercise efficiency and performance in endurance trained subjects. Furthermore it appears difficult to improve VO2 kinetics with intensified training in trained athletes; however intense exercise can amplify the VO2 response during subsequent high......In response to an increase in the metabolic demand the oxygen uptake (VO2) increases in an exponential fashion in exercising muscles and stabilizes after 1-2 min eventually reaching a plateau or steady state where the energy demand is matched by the l vel of VO2. VO2 kinetics describes the distinct...... phases of the VO2 response at the onset of exercise. Fast VO2 kinetics are considered to be beneficial in intense endurance sports with competitions lasting ~2-8 min, whereas low VO2 at steady state (high efficiency) is considered beneficial especially in events of longer duration. To improve...

  14. Influence of cerebrovascular arteriosclerosis on cerebral oxygenation during exercise

    International Nuclear Information System (INIS)

    Nagayama, Osamu; Koike, Akira; Hoshimoto, Masayo; Yamaguchi, Kaori; Tajima, Akihiko; Goda, Ayumi; Uejima, Tokuhisa; Aizawa, Tadanori; Itoh, Haruki

    2007-01-01

    Although it is assumed that cerebral oxygenation during exercise is influenced by both cardiopulmonary function and cerebrovascular arteriosclerosis, the latter factor has not been fully clarified. In the present study the relationship between the degree of cerebrovascular arteriosclerosis and cerebral oxygenation during exercise was investigated. A total of 109 patients (69 patients with coronary artery disease, 40 patients with hypertensive heart disease) (61.7±9.7 years) performed a symptom-limited exercise test with respiratory gas measurements (CPX). From the respiratory gas analysis, peak O 2 uptake (VO 2 ), the slope of the increase in VO 2 to the increase in work rate (ΔVO 2 /ΔWR), and the slope of the increase in ventilation to the increase in CO 2 output (VE/VCO 2 slope) were calculated. Oxyhemoglobin (O 2 Hb) at the forehead was monitored using near-infrared spectroscopy. The brain ischemic score was counted based upon fluid-attenuated inversion recovery images of magnetic resonance imaging and expressed from 0 to 4. When compared with patients with a lower ischemic score ( 2 Hb during exercise (-1.08±2.7 vs 0.77±4.1 μmol/L, p=0.011). Of brain ischemic score, left ventricular ejection fraction, peak VO 2 , ΔVO 2 /ΔWR, and the VE/VCO 2 slope, ΔVO 2 /ΔWR was found to be the sole independent index determining cerebral O 2 Hb during exercise. The CPX parameters were also significantly related to the degree of cerebrovascular arteriosclerosis. Although cerebral oxygenation during exercise is mainly related to cardiopulmonary function, the degree of cerebrovascular arteriosclerosis partly influences cerebral oxygenation in patients with risk factors for atherosclerosis. (author)

  15. Effect of oxygen vacancies on magnetic and transport properties of Sr2IrO4

    Science.gov (United States)

    Dwivedi, Vinod Kumar; Mukhopadhyay, Soumik

    2018-05-01

    Iridates have recently attracted growing interest because of their potential for realizing various interesting phases like interaction driven Mott-type insulator and magnetically driven Slater-type. In this paper, we present the magnetic and electrical transport properties of polycrystalline Sr2IrO4 synthesized by solid state reaction route. We find a ferromagnetic transition at 240 K. The Curie-Weiss law behavior hold good above the magnetic transition temperature TMag = 240 K with a small effective paramagnetic magnetic moment μeff = 0.25 µB/f.u. and a Curie-Weiss temperature, θCW = +100 K. Zero field cooled (ZFC) magnetization shows a gradual dcrease below 150 K, while same for field cooled (FC) below 50 K. Interestingly, below temperatures, ⁓ 10 K, a sharp increase in ZFC and FC magnetization can be seen. A temperature dependent resistivity reveals insulating behavior followed by power law mechanism. The sintering of sample in air leads to the very low value of resistivity is likely related to Sr or oxygen vacancies.

  16. Vastly Enhanced BiVO4 Photocatalytic OER Performance by NiCoO2 as Cocatalyst

    KAUST Repository

    Palaniselvam, Thangavelu

    2017-08-07

    Here, a simple and efficient preparation of NiCoO nanoparticle modified nanoporous bismuth vanadate (BiVO) thin film and its application in photoelectrocatalytic (PEC) oxygen evolution reaction (OER) is demonstrated. The role of NiCoO in the composite electrode (BiVO/NiCoO) is twofold: OER cocatalyst and band structure modifier. It improves surface reaction kinetics for PEC OER and enhances charge separation efficiency simultaneously, which is believed to be a determining factor for the unprecedentedly high PEC OER performance of this BiVO/NiCoO nanocomposite. The photocurrent density of 3.6 mA cm at 1.23 V versus RHE in 0.1 m potassium phosphate buffered (pH = 7) electrolyte by BiVO/NiCoO is three times that of BiVO and significantly higher than most literature values. The BiVO/NiCoO nanocomposite shows/possess a high charge separation efficiency (η) of ≈72% as compared to only 23% for pure nanoporous BiVO at 1.23 V versus RHE, which demonstrates convincing role of NiCoO in the composite electrode. Both the excellent photocurrent density and great operational stability of this BiVO/NiCoO nanocomposite makes it a promising photocatalytic material for practical applications.

  17. Electron diffraction study of the sillenites Bi12SiO20, Bi25FeO39 and Bi25InO39: Evidence of short-range ordering of oxygen-vacancies in the trivalent sillenites

    Directory of Open Access Journals (Sweden)

    Craig A. Scurti

    2014-08-01

    Full Text Available We present an electron diffraction study of three sillenites, Bi12SiO20, Bi25FeO39, and Bi25InO39 synthesized using the solid-state method. We explore a hypothesis, inspired by optical studies in the literature, that suggests that trivalent sillenites have additional disorder not present in the tetravalent compounds. Electron diffraction patterns of Bi25FeO39 and Bi25InO39 show streaks that confirm deviations from the ideal sillenite structure. Multi-slice simulations of electron-diffraction patterns are presented for different perturbations to the sillenite structure - partial substitution of the M site by Bi3+, random and ordered oxygen-vacancies, and a frozen-phonon model. Although comparison of experimental data to simulations cannot be conclusive, we consider the streaks as evidence of short-range ordered oxygen-vacancies.

  18. Hexagonal perovskites with cationic vacancies. 29. Structure of Ba/sub 4/ScReWvacantO/sub 12/ - on the function of octahedral cationic vacancies in perovskite stacking polytypes

    Energy Technology Data Exchange (ETDEWEB)

    Kemmler-Sack, S; Herrmann, M [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

    1981-09-01

    The hexagonal perovskite stacking polytype Ba/sub 4/ScReWvacantO/sub 12/ crystallizes in a rhombohedral 12 L structure (space group R-3m; sequence (hhcc)/sub 3/). The refined, intensity related R' value is 6.6%. The octahedral net consists of blocks of three face connected octahedra with a central vacancy, in the two outer positions the rhenium and tungsten atoms are located; these units are linked via common corners by single octahedra, occupied with scandium. The construction principles of hexagonal oxygen perovskites with octahedral, cationic vacancies are reported.

  19. Insulator-metal transition in substrate-independent VO2 thin film for phase-change devices.

    Science.gov (United States)

    Taha, Mohammad; Walia, Sumeet; Ahmed, Taimur; Headland, Daniel; Withayachumnankul, Withawat; Sriram, Sharath; Bhaskaran, Madhu

    2017-12-20

    Vanadium has 11 oxide phases, with the binary VO 2 presenting stimuli-dependent phase transitions that manifest as switchable electronic and optical features. An elevated temperature induces an insulator-to-metal transition (IMT) as the crystal reorients from a monoclinic state (insulator) to a tetragonal arrangement (metallic). This transition is accompanied by a simultaneous change in optical properties making VO 2 a versatile optoelectronic material. However, its deployment in scalable devices suffers because of the requirement of specialised substrates to retain the functionality of the material. Sensitivity to oxygen concentration and larger-scale VO 2 synthesis have also been standing issues in VO 2 fabrication. Here, we address these major challenges in harnessing the functionality in VO 2 by demonstrating an approach that enables crystalline, switchable VO 2 on any substrate. Glass, silicon, and quartz are used as model platforms to show the effectiveness of the process. Temperature-dependent electrical and optical characterisation is used demonstrating three to four orders of magnitude in resistive switching, >60% chromic discrimination at infrared wavelengths, and terahertz property extraction. This capability will significantly broaden the horizon of applications that have been envisioned but remained unrealised due to the lack of ability to realise VO 2 on any substrate, thereby exploiting its untapped potential.

  20. Characterization of oxygen vacancies and their migration in Ba-doped Pb(Zr0.52Ti0.48)O3 ferroelectrics

    Science.gov (United States)

    Zhang, M. F.; Wang, Y.; Wang, K. F.; Zhu, J. S.; Liu, J.-M.

    2009-03-01

    We investigate in detail the migration kinetics of oxygen vacancies (OVs) in Ba-doped Pb(Zr0.52Ti0.48)O3 (PZT) ferroelectrics by complex impedance spectroscopy. The temperature dependent dc-electrical conductivity σdc suggests that Ba doping into PZT can lower significantly the density of OVs, leading to the distinctly decreased σdc and slightly enhanced activation energy U for the migration of OVs, thus benefiting the polarization fatigue resistance. Furthermore, the polarization fluctuation induced by the relaxation of OVs is reduced by the Ba doping. The Cole-Cole fitting to the dielectric loss manifests strong correlation among OVs, and the migration of OVs appears to be a collective behavior.

  1. Effects of temperature and hypoxic stress on the oxygen ...

    African Journals Online (AJOL)

    The specific oxygen consumption rate (VO2lMb) of Labeo capensis, the freshwater mudsucker, was determined for small and large fish at winter (8°C) and summer (23°C) temperatures. VO2lMb was also determined during hypoxic conditions of the experimental water. It was found that VO2lMb does not differ substantially ...

  2. Time limit and time at VO2max' during a continuous and an intermittent run.

    Science.gov (United States)

    Demarie, S; Koralsztein, J P; Billat, V

    2000-06-01

    The purpose of this study was to verify, by track field tests, whether sub-elite runners (n=15) could (i) reach their VO2max while running at v50%delta, i.e. midway between the speed associated with lactate threshold (vLAT) and that associated with maximal aerobic power (vVO2max), and (ii) if an intermittent exercise provokes a maximal and/or supra maximal oxygen consumption longer than a continuous one. Within three days, subjects underwent a multistage incremental test during which their vVO2max and vLAT were determined; they then performed two additional testing sessions, where continuous and intermittent running exercises at v50%delta were performed up to exhaustion. Subject's gas exchange and heart rate were continuously recorded by means of a telemetric apparatus. Blood samples were taken from fingertip and analysed for blood lactate concentration. In the continuous and the intermittent tests peak VO2 exceeded VO2max values, as determined during the incremental test. However in the intermittent exercise, peak VO2, time to exhaustion and time at VO2max reached significantly higher values, while blood lactate accumulation showed significantly lower values than in the continuous one. The v50%delta is sufficient to stimulate VO2max in both intermittent and continuous running. The intermittent exercise results better than the continuous one in increasing maximal aerobic power, allowing longer time at VO2max and obtaining higher peak VO2 with lower lactate accumulation.

  3. Possible factors determining the non-linearity in the VO2-power output relationship in humans: theoretical studies.

    Science.gov (United States)

    Korzeniewski, Bernard; Zoladz, Jerzy A

    2003-08-01

    At low power output exercise (below lactate threshold), the oxygen uptake increases linearly with power output, but at high power output exercise (above lactate threshold) some additional oxygen consumption causes a non-linearity in the overall VO(2) (oxygen uptake rate)-power output relationship. The functional significance of this phenomenon for human exercise tolerance is very important, but the mechanisms underlying it remain unknown. In the present work, a computer model of oxidative phosphorylation in intact skeletal muscle developed previously is used to examine the background of this relationship in different modes of exercise. Our simulations demonstrate that the non-linearity in the VO(2)-power output relationship and the difference in the magnitude of this non-linearity between incremental exercise mode and square-wave exercise mode (constant power output exercise) can be generated by introducing into the model some hypothetical factor F (group of associated factors) that accumulate(s) in time during exercise. The performed computer simulations, based on this assumption, give proper time courses of changes in VO(2) and [PCr] after an onset of work of different intensities, including the slow component in VO(2), well matching the experimental results. Moreover, if it is assumed that the exercise terminates because of fatigue when the amount/intensity of F exceed some threshold value, the model allows the generation of a proper shape of the well-known power-duration curve. This fact suggests that the phenomenon of the non-linearity of the VO(2)-power output relationship and the magnitude of this non-linearity in different modes of exercise is determined by some factor(s) responsible for muscle fatigue.

  4. A first-principles study of oxygen vacancy induced changes in structural, electronic and magnetic properties of La{sub 2/3}Sr{sub 1/3}MnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jia [Division of Materials Science, Nanyang Technological University, Singapore, 639798 (Singapore); Sun, Lizhong [Division of Materials Science, Nanyang Technological University, Singapore, 639798 (Singapore); Laboratory for Quantum Engineering and Micro-Nano Energy Technology, Xiangtan University, Xiangtan, Hunan, 411105 (China); Shenai, Prathamesh M.; Wang, Junling [Division of Materials Science, Nanyang Technological University, Singapore, 639798 (Singapore); Zheng, Hang [Department of Physics, Shanghai Jiao Tong University, 800 Dong Chuan Road, Shanghai, 200240 (China); Zhao, Yang, E-mail: YZhao@ntu.edu.sg [Division of Materials Science, Nanyang Technological University, Singapore, 639798 (Singapore)

    2015-11-15

    We have systematically assessed the influence of oxygen vacancy defects on the structural, electronic and magnetic properties of La{sub 2/3}Sr{sub 1/3}MnO{sub 3} via first-principles calculations using the bare GGA as well as the GGA + U formalism. The on-site Coulombic repulsion parameter U for Mn 3d orbital in the latter has been determined by the linear response theory. It is revealed that the introduction of the vacancy defects causes prominent structural changes in the microenvironment of a defect including the distortions of MnO{sub 6} octahedra. In contrast to the general notion, the GGA + U formalism is found to yield significantly more prominent structural changes than the bare GGA method. The octahedral distortion leads to a strengthening or weakening of the hybridization between Mn 3d and O 2p orbitals depending upon an increase or decrease, respectively, in the Mn–O distances as compared to the pristine system. The magnetic moments of the Mn atoms located in three typical sites of the vacancy-containing supercell are all larger than those in the pristine system. This enhancement for the Mn atoms located in the first- and third-nearest neighboring MnO{sub 6} octahedra of the vacancy defect originates from the electron transfer from 4s/3p to 3d orbitals. On the other hand, for the Mn atom located in the first-nearest neighboring site of the vacancy it is attributed to the increased total number of electrons in 3d orbitals due to the absence of one Mn–O bond. Furthermore, we have characterized the O-vacancy defect as a hole-type defect that forms a negative charge center, attracting electrons. - Highlights: • GGA + U calculations reveal effect of O-vacancy on properties of La{sub 1−1/3}Sr{sub 1/3}MnO{sub 3.} • Value of U = 5.9 eV calculated for Mn 3d orbitals from the linear response theory. • O-vacancy causes prominent distortions of MnO{sub 6} octahedra. • Octahedral distortions modulate electronic and magnetic properties of LSMO.

  5. Stoichiometry control of SrVO{sub 3} thin films grown by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Scheiderer, Philipp; Schmitt, Matthias; Sing, Michael; Claessen, Ralph [Universitaet Wuerzburg, Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), 97074 Wuerzburg (Germany)

    2016-07-01

    Oxide heterostructures exhibit fascinating properties, e.g., the coexistence of superconductivity and ferromagnetism at the interface of LaAlO{sub 3}/SrTiO{sub 3}, but the extraordinary electronic properties of transition metal oxides caused by electron correlation yet wait to be fully harnessed. One suitable candidate for future device applications is the correlated metal SrVO{sub 3}, which can be prepared by pulsed laser deposition (PLD) on commonly used substrates such as SrTiO{sub 3}. Sample fabrication by PLD offers a wide variety of possibilities to manipulate the structural and electronic properties of the grown films in a controlled way. Here we report on the manipulation of the cation and oxygen stoichiometry of SrVO{sub 3} thin films by tuning the laser flux density of the PLD-ablation process and the oxygen background pressure during growth, respectively. In situ photoemission, x-ray diffraction, and temperature dependent resistivity measurements enable us to monitor the structural and electronic changes: Cation off-stoichiometry causes a strong increase of the out-of-plane lattice constant as well as a lower residual resistivity ratio, while excess oxygen is found to induce a shift to higher vanadium valences. After exposure to air a similar shift is detected, indicating an overoxidation of the SrVO{sub 3} film.

  6. 'Multi-associations': predisposed to misinterpretation of peripheral tissue oxygenation and circulation in neonates.

    Science.gov (United States)

    Pichler, Gerhard; Pocivalnik, Mirjam; Riedl, Regina; Pichler-Stachl, Elisabeth; Morris, Nicholas; Zotter, Heinz; Müller, Wilhelm; Urlesberger, Berndt

    2011-08-01

    Interpretation of peripheral circulation in ill neonates is crucial but difficult. The aim was to analyse parameters potentially influencing peripheral oxygenation and circulation. In a prospective observational cohort study in 116 cardio-circulatory stable neonates, peripheral muscle near-infrared spectroscopy (NIRS) with venous occlusion was performed. Tissue oxygenation index (TOI), mixed venous oxygenation (SvO(2)), fractional oxygen extraction (FOE), fractional tissue oxygen extraction (FTOE), haemoglobin flow (Hbflow), oxygen delivery (DO(2)), oxygen consumption (VO(2)), and vascular resistance (VR) were assessed. Correlation coefficients between NIRS parameters and demographic parameters (gestational age, birth weight, age, actual weight, diameter of calf, subcutaneous adipose tissue), monitoring parameters (heart rate, arterial oxygen saturation (SaO(2)), mean blood pressure (MAP), core/peripheral temperature, central/peripheral capillary refill time) and laboratory parameters (haemoglobin concentration (Hb-blood), pCO(2)) were calculated. All demographic parameters except for Hbflow and DO(2) correlated with NIRS parameters. Heart rate correlated with TOI, SvO(2), VO(2) and VR. SaO(2) correlated with FOE/FTOE. MAP correlated with Hbflow, DO(2), VO(2) and VR. Core temperature correlated with FTOE. Peripheral temperature correlated with all NIRS parameters except VO(2). Hb-blood correlated with FOE and VR. pCO(2) levels correlated with TOI and SvO(2). The presence of multiple interdependent factors associated with peripheral oxygenation and circulation highlights the difficulty in interpreting NIRS data. Nevertheless, these findings have to be taken into account when analysing peripheral oxygenation and circulation data.

  7. Relationship between running kinematic changes and time limit at vVO2max

    Directory of Open Access Journals (Sweden)

    Leonardo De Lucca

    2012-06-01

    Exhaustive running at maximal oxygen uptake velocity (vVO2max can alter running kinematic parameters and increase energy cost along the time. The aims of the present study were to compare characteristics of ankle and knee kinematics during running at vVO2max and to verify the relationship between changes in kinematic variables and time limit (Tlim. Eleven male volunteers, recreational players of team sports, performed an incremental running test until volitional exhaustion to determine vVO2max and a constant velocity test at vVO2max. Subjects were filmed continuously from the left sagittal plane at 210 Hz for further kinematic analysis. The maximal plantar flexion during swing (p<0.01 was the only variable that increased significantly from beginning to end of the run. Increase in ankle angle at contact was the only variable related to Tlim (r=0.64; p=0.035 and explained 34% of the performance in the test. These findings suggest that the individuals under study maintained a stable running style at vVO2max and that increase in plantar flexion explained the performance in this test when it was applied in non-runners.

  8. MAXIMAL OXIGEN UPTAKE (VO2 MAX AS THE INDICATOR OF PHYSICAL WORKING CAPACITY IN SPORTSMEN

    Directory of Open Access Journals (Sweden)

    Zvezdana Rajkovaca

    2005-12-01

    Full Text Available The term “aerobic capacity” represents the sum of aerobic metabolic processes in human organism. It is the basis of the physical working capacity. Value of the maximal oxygen uptake (VO2max is the best indicator for the aerobic capacity evaluation.The purpose of this study was to check the possibility of using VO2max as the indicator of aerobic capacity in sportsmen and to check differences in VO2max values in regard to non-sportsmen.The goals were: 1.Analyses of the VO2max values in sportsmen of various sports 2. Comparison of values of sportsmen with the values of non-sportsmen.This study included 67 sportsmen (rowers, football players and judoists and 28 nonsportsmen. VO2max was measured by using a direct method.The results obtained show statistically higher VO2max values in rowers (4,52 L/min - 55,8 mL/kg/min in regard to football players (4,2 L/min – 53,6 mL/kg/min, judoists (3,58 L/min - 47,2 mL/ kg/min and non-sportsmen (3,28 L/min – 42,3 mL/kg/min. Successful rowing requires high anaerobic capacity and, therefore, high VO2max.These results show higher values of VO2max in sportsmen in regard to non-sportsmen, which is the result of training only.

  9. Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO{sub 2{+-}x}

    Energy Technology Data Exchange (ETDEWEB)

    Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert [Institute of Materials Science, Technische Universitaet Darmstadt, 64287 Darmstadt (Germany)

    2012-12-01

    We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO{sub 2{+-}x} grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.

  10. High-throughput DFT calculations of formation energy, stability and oxygen vacancy formation energy of ABO3 perovskites

    Science.gov (United States)

    Emery, Antoine A.; Wolverton, Chris

    2017-10-01

    ABO3 perovskites are oxide materials that are used for a variety of applications such as solid oxide fuel cells, piezo-, ferro-electricity and water splitting. Due to their remarkable stability with respect to cation substitution, new compounds for such applications potentially await discovery. In this work, we present an exhaustive dataset of formation energies of 5,329 cubic and distorted perovskites that were calculated using first-principles density functional theory. In addition to formation energies, several additional properties such as oxidation states, band gap, oxygen vacancy formation energy, and thermodynamic stability with respect to all phases in the Open Quantum Materials Database are also made publicly available. This large dataset for this ubiquitous crystal structure type contains 395 perovskites that are predicted to be thermodynamically stable, of which many have not yet been experimentally reported, and therefore represent theoretical predictions. The dataset thus opens avenues for future use, including materials discovery in many research-active areas.

  11. Positron annihilation study of vacancy-type defects in fast-neutron-irradiated MgO·nAl{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, Abu Zayed Mohammad Saliqur, E-mail: zayed82000@yahoo.com [Key Laboratory of Nuclear Analytical Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquanlu Shijingshan District, Beijing 100049 (China); Li, Zhuoxin; Cao, Xingzhong; Wang, Baoyi; Wei, Long [Key Laboratory of Nuclear Analytical Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquanlu Shijingshan District, Beijing 100049 (China); Xu, Qiu [Reactor Research Institute, Kyoto University 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494 (Japan); Atobe, Kozo [Nuclear Safety Technology Center, 9-15, 1-chome, Utsubohonmachi, Nishi Ku, Osaka 550-0004 (Japan)

    2014-09-15

    Highlights: •Detection of Al monovacancy by positron lifetime spectroscopy in fast neutron-irradiated MgO·nAl{sub 2}O{sub 3}(n=2). •Concentration of defects is also estimated for Al monovacancy. •O atom peak was observed by using coincidence Doppler broadening spectroscopy. -- Abstract: The positron lifetimes of fast-neutron-irradiated MgO·nAl{sub 2}O{sub 3} single crystals were measured to investigate the formation of cation vacancies. Al monovacancy was possibly observed in samples irradiated by fast neutrons at ultra-low temperatures. Additionally, vacancy-oxygen complex centers were possibly observed in samples irradiated at higher temperatures and fast neutron fluences. Coincidence Doppler broadening (CDB) spectra were measured to obtain information regarding the vicinity of vacancy-type defects. A peak at approximately 11 × 10{sup −3} m{sub 0}c was observed, which may be due to the presence of oxygen atoms in the neighborhood of the vacancies.

  12. Magnetoresistance Versus Oxygen Deficiency in Epi-stabilized SrRu1 - x Fe x O3 - δ Thin Films

    Science.gov (United States)

    Dash, Umasankar; Acharya, Susant Kumar; Lee, Bo Wha; Jung, Chang Uk

    2017-03-01

    Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxide materials. Here, we studied the influence of oxygen vacancies on the magnetoresistance (MR) properties of SrRu1 - x Fe x O3 - δ epitaxial thin films ( x = 0.10, 0.20, and 0.30). For this purpose, we synthesized highly strained epitaxial SrRu1 - x Fe x O3 - δ thin films with atomically flat surfaces containing different amounts of oxygen vacancies using pulsed laser deposition. Without an applied magnetic field, the films with x = 0.10 and 0.20 showed a metal-insulator transition, while the x = 0.30 thin film showed insulating behavior over the entire temperature range of 2-300 K. Both Fe doping and the concentration of oxygen vacancies had large effects on the negative MR contributions. For the low Fe doping case of x = 0.10, in which both films exhibited metallic behavior, MR was more prominent in the film with fewer oxygen vacancies or equivalently a more metallic film. For semiconducting films, higher MR was observed for more semiconducting films having more oxygen vacancies. A relatively large negative MR ( 36.4%) was observed for the x = 0.30 thin film with a high concentration of oxygen vacancies ( δ = 0.12). The obtained results were compared with MR studies for a polycrystal of (Sr1 - x La x )(Ru1 - x Fe x )O3. These results highlight the crucial role of oxygen stoichiometry in determining the magneto-transport properties in SrRu1 - x Fe x O3 - δ thin films.

  13. Nature of oxygen donors and radiation defects in oxygen-doped germanium

    International Nuclear Information System (INIS)

    Fukuoka, Noboru; Atobe, Kozo; Honda, Makoto; Matsuda, Koji.

    1991-01-01

    The nature of oxygen donors and radiation defects in oxygen-doped germanium were studied through measurements of the infrared absorption spectrum, deep level transient spectroscopy spectrum and carrier concentration. It is revealed that a new donor is not formed in oxygen-doped germanium. An A-center (interstitial oxygen-vacancy pair) forms a complex with a thermal donor in its annealing stage at 60degC-140degC. The introduction rate of defects by 1.5 MeV electron irradiation was enhanced in thermal-donor-doped samples. (author)

  14. Modulation of resistive switching characteristics for individual BaTiO3 microfiber by surface oxygen vacancies

    Science.gov (United States)

    Miao, Zhilei; Chen, Lei; Zhou, Fang; Wang, Qiang

    2018-01-01

    Different from traditional thin-film BaTiO3 (BTO) RRAM device with planar structure, individual microfiber-shaped RRAM device, showing promising application potentials in the micro-sized non-volatile memory system, has not been investigated so far to demonstrate resistive switching behavior. In this work, individual sol-gel BTO microfiber has been formed using the draw-bench method, followed by annealing in different atmospheres of air and argon, respectively. The resistive switching characteristics of the individual BTO microfiber have been investigated by employing double-probe SEM measurement system, which shows great convenience to test local electrical properties by modulating the contact sites between the W probes and the BTO microfiber. For the sample annealed in air, the average resistive ON/OFF ratio is as high as 108, enhanced about four orders in comparison with the counterpart that annealed in Argon. For the sample annealed in argon ambience, the weakened resistive ON/OFF ratio can be attributed to the increased presence of oxygen vacancies in the surface of BTO fibers, and the underlying electrical conduction mechanisms are also discussed.

  15. Density functional study on the heterogeneous oxidation of NO over α-Fe_2O_3 catalyst by H_2O_2: Effect of oxygen vacancy

    International Nuclear Information System (INIS)

    Song, Zijian; Wang, Ben; Yu, Jie; Ma, Chuan; Zhou, Changsong; Chen, Tao; Yan, Qianqian; Wang, Ke; Sun, Lushi

    2017-01-01

    Highlights: • NO and H_2O_2 adsorption on perfect and oxygen defect α-Fe_2O_3 (0 0 1) surface were studied by DFT calculations. • H_2O_2 shows high chemical reactivity for its adsorption on oxygen defect α-Fe_2O_3 (0 0 1) surface. • Oxygen vacancy plays an important role of the catalytic oxidation of NO by H_2O_2 over the α-Fe_2O_3 catalyst surfaces. • Mechanism of NO oxidation over α-Fe_2O_3 (0 0 1) surface by H_2O_2 was explained. - Abstract: Catalytic oxidation with H_2O_2 is a promising method for NOx emission control in coal-fired power plants. Hematite-based catalysts are attracting increased attention because of their surface redox reactivity. To elucidate the NO oxidation mechanism on α-Fe_2O_3 surfaces, density functional theory (DFT) calculations were conducted by investigating the adsorption characteristics of nitric oxide (NO) and hydrogen peroxide (H_2O_2) on perfect and oxygen defect α-Fe_2O_3 (0 0 1) surfaces. Results show that NO was molecularly adsorbed on two kinds of surfaces. H_2O_2 adsorption on perfect surface was also in a molecular form; however, H_2O_2 dissociation occurred on oxygen defect α-Fe_2O_3 (0 0 1) surface. The adsorption intensities of the two gas molecules in perfect α-Fe_2O_3 (0 0 1) surface followed the order NO > H_2O_2, and the opposite was true for the oxygen defect α-Fe_2O_3 (0 0 1). Oxygen vacancy remarkably enhanced the adsorption intensities of NO and H_2O_2 and promoted H_2O_2 decomposition on catalyst surface. As an oxidative product of NO, HNO_2 was synthesized when NO and H_2O_2 co-adsorbed on the oxygen defect α-Fe_2O_3 (0 0 1) surface. Analyses of Mulliken population, electron density difference, and partial density of states showed that H_2O_2 decomposition followed the Haber–Weiss mechanism. The trends of equilibrium constants suggested that NO adsorption on α-Fe_2O_3 (0 0 1) surface was more favorable at low than at high temperatures, whereas H_2O_2 adsorption was favorable between 375 and

  16. Biochemical background of the VO2 on-kinetics in skeletal muscles.

    Science.gov (United States)

    Korzeniewski, Bernard; Zoladz, Jerzy A

    2006-02-01

    This review discusses the present knowledge on the oxygen uptake kinetics at the onset of exercise in skeletal muscle and the contribution of a previously developed computer model of oxidative phosphorylation in intact skeletal muscle to the understanding of the factors determining this kinetics on the biochemical level. It has been demonstrated recently that an increase in the total creatine pool [PCr + Cr] and in glycolytic ATP supply lengthen the half-transition time of the VO2 on-kinetics, while an increase in mitochondria content, in parallel activation of ATP supply and ATP usage, in muscle oxygen concentration, in proton leak, in resting energy demand, in resting cytosolic pH, and in initial alkalization diminish this parameter. It has also been shown that the half-transition time is near-linearly proportional to the absolute difference between the phosphocreatine concentration during work and at rest (deltaPCr). The present review discusses whether the V/O2 on-kinetics on the muscle level is strictly or only approximately exponential. Finally, it is postulated that a short transition time of the VO2 on-kinetics in itself does not need be profitable for the skeletal muscle functioning during exercise, but usually a short transition time is correlated with factors that improve exercise capacity. The transition time is a phenomenological parameter resulting from the biochemical properties of the system and not a physical factor that can cause anything in the system.

  17. Why is VO2 max after altitude acclimatization still reduced despite normalization of arterial O2 content?

    DEFF Research Database (Denmark)

    Calbet, J A L; Boushel, Robert Christopher; Radegran, G

    2003-01-01

    Acute hypoxia (AH) reduces maximal O2 consumption (VO2 max), but after acclimatization, and despite increases in both hemoglobin concentration and arterial O2 saturation that can normalize arterial O2 concentration ([O2]), VO2 max remains low. To determine why, seven lowlanders were studied at VO2......% of the cardiac output perfused the legs, in CH the legs received only 67%. Pulmonary VO2 max (4.1 +/- 0.3 l/min at SL) fell to 2.2 +/- 0.1 l/min in AH (P normalization...... of arterial [O2] is explained by two circulatory effects of altitude: 1) failure of cardiac output to normalize and 2) preferential redistribution of cardiac output to nonexercising tissues. Oxygen transport from blood to muscle mitochondria, on the other hand, appears unaffected by CH....

  18. Tuning the electronic structure of SrTiO3/SrFeO3−x superlattices via composition and vacancy control

    Directory of Open Access Journals (Sweden)

    Robert F. Berger

    2014-04-01

    Full Text Available Using density functional theory-based calculations, we explore the effects of oxygen vacancies and epitaxial layering on the atomic, magnetic, and electronic structure of (SrTiO3n(SrFeO3−x1 superlattices. While structures without oxygen vacancies (x = 0 possess small or non-existent band gaps and ferromagnetic ordering in their iron layers, those with large vacancy concentrations (x = 0.5 have much larger gaps and antiferromagnetic ordering. Though the computed gaps depend numerically on the delicate energetic balance of vacancy ordering and on the value of Hubbard U eff used in the calculations, we demonstrate that changes in layering can tune the band gaps of these superlattices below that of SrTiO3 (3.2 eV by raising their valence band maxima. This suggests the possibility that these superlattices could absorb in the solar spectrum, and could serve as water-splitting photocatalysts.

  19. Prognostic impact of peakVO2-changes in stable CHF on chronic beta-blocker treatment.

    Science.gov (United States)

    Frankenstein, L; Nelles, M; Hallerbach, M; Dukic, D; Fluegel, A; Schellberg, D; Katus, H A; Remppis, A; Zugck, C

    2007-11-15

    Peak oxygen uptake (pVO2) is used for risk stratification in chronic heart failure (CHF), but little is known about the prognostic impact of pVO2-changes in patients on chronic beta-blocker (BBL) therapy. We therefore prospectively evaluated individual pVO2-changes at a 6-month interval in patients all receiving BBL. 194 patients with stable CHF on stable medication were included (V1) and underwent clinical evaluation and exercise testing. Testing was repeated (V2) at 5.7+/-1.5 months after V1 and patients were followed >12 months after V2. Death or hospitalisation due to cardiac reasons was the predefined EP (EPP, end-point positive; n=62; EPN, end-point negative; n=113). Initial characteristics did not differ between EPP and EPN. Multivariate cox regression analysis revealed that change of pVO2 (EPP: -0.6+/-2.6 ml/kg min; EPN: +2.5+/-3.3 ml/kg min; p<0.001) was independent to pVO2, LVEF, NTproBNP and NYHA at V2 for prediction of the combined end-point during follow-up. An increase of pVO2 by 10% was identified as an adequate cut-off value for risk stratification and ROC-analysis showed the significant incremental prognostic value of the determination of pVO2 changes in combination with pVO2. Serial measurements of pVO2 yield additional information for risk stratification in clinically homogenous CHF patients receiving BBL. This is the first study demonstrating this fact within a narrow predefined interval with all patients on BBL.

  20. COMPARISON OF OXYGEN UPTAKE KINETICS AND OXYGEN DEFICIT IN SEVERELY OVERWEIGHT AND NORMAL WEIGHT ADOLESCENT FEMALES

    Directory of Open Access Journals (Sweden)

    Mark Loftin

    2005-12-01

    Full Text Available The purpose of this study was to determine if differences in oxygen uptake kinetics and oxygen deficit existed between normal weight and severely overweight adolescent girls. Subjects included 10 normal weight and 8 severely overweight girls. The participants performed a leg cycling VO2 peak test and a constant load leg cycling test at 80% of the ventilatory threshold (T-vent. In the constant workload test O2 kinetics as indicated by Phase I (VO2 L at 20 sec and Phase II time constants (t were determined. Also, the O2 deficit (VO2 L was measured. As expected significant differences were noted in body composition and VO2 peak relative to mass with normal weight body mass averaging 55.3 ± 7.0 kg, severely overweight 90.5 ± 18.0 kg, % fat normal weight 27.3 ± 3.9%, severely overweight 49.7 ± 4.9% and VO2 peak (ml·kg-1·min-1 normal weight 32.0 ± 2.7 and severely overweight 22.0 ± 5.3. VO2 peak (l·min-1 and T-vent (%VO2 max were similar between groups. Results revealed similar O2 kinetic responses between groups; phase I kinetics normal weight 0.72 ± 0.15 L; severely overweight 0.75 ± 0.13L, phase II (t normal weight 41.5 ± 21.3 sec; severely overweight 33.9 ± 22.7 sec. However, the O2 deficit was significantly higher in the severely overweight (0.75 ± 0.15L when compared to the normal weight group (0.34 ± 0.13L. Correlations ranged from r = -0.15 to 0.51 between VO2 peak (L·min-1 or fat weight and phase I, t and O2 deficit. These data generally support previous research concerning the independence of O2 uptake response and body size

  1. Study of the degradation and recovery of the optical properties of H+-implanted ZnO pigments

    Science.gov (United States)

    Li, Chundong; Lv, Jinpeng; Yao, Shulong; Hu, Jiangang; Liang, Zhiqiang

    2013-01-01

    We studied the influences of proton implantation and oxygen post-annealing on the optical properties of ZnO pigments using a combination of Raman scattering, positron annihilation and photoluminescence techniques. Raman scattering results indicated that oxygen vacancies and interstitial zinc defects were produced after proton implantation. Positron annihilation spectroscopy and photoluminescence measurements demonstrated that the zinc vacancies do not contribute to the optical absorption, but give rise to the visible band emission. Interestingly, the proton implantation induced optical degradation can be annealed out at 800 °C in an O2 atmosphere. We conclude that the defect centers responsible for the optical absorption are primarily composed of VO+, ionized Zni and ionized Oi.

  2. 'Multi-associations': predisposed to misinterpretation of peripheral tissue oxygenation and circulation in neonates

    International Nuclear Information System (INIS)

    Pichler, Gerhard; Pocivalnik, Mirjam; Pichler-Stachl, Elisabeth; Morris, Nicholas; Zotter, Heinz; Müller, Wilhelm; Urlesberger, Berndt; Riedl, Regina

    2011-01-01

    Interpretation of peripheral circulation in ill neonates is crucial but difficult. The aim was to analyse parameters potentially influencing peripheral oxygenation and circulation. In a prospective observational cohort study in 116 cardio-circulatory stable neonates, peripheral muscle near-infrared spectroscopy (NIRS) with venous occlusion was performed. Tissue oxygenation index (TOI), mixed venous oxygenation (SvO 2 ), fractional oxygen extraction (FOE), fractional tissue oxygen extraction (FTOE), haemoglobin flow (Hbflow), oxygen delivery (DO 2 ), oxygen consumption (VO 2 ), and vascular resistance (VR) were assessed. Correlation coefficients between NIRS parameters and demographic parameters (gestational age, birth weight, age, actual weight, diameter of calf, subcutaneous adipose tissue), monitoring parameters (heart rate, arterial oxygen saturation (SaO 2 ), mean blood pressure (MAP), core/peripheral temperature, central/peripheral capillary refill time) and laboratory parameters (haemoglobin concentration (Hb-blood), pCO 2 ) were calculated. All demographic parameters except for Hbflow and DO 2 correlated with NIRS parameters. Heart rate correlated with TOI, SvO 2 , VO 2 and VR. SaO 2 correlated with FOE/FTOE. MAP correlated with Hbflow, DO 2 , VO 2 and VR. Core temperature correlated with FTOE. Peripheral temperature correlated with all NIRS parameters except VO 2 . Hb-blood correlated with FOE and VR. pCO 2 levels correlated with TOI and SvO 2 . The presence of multiple interdependent factors associated with peripheral oxygenation and circulation highlights the difficulty in interpreting NIRS data. Nevertheless, these findings have to be taken into account when analysing peripheral oxygenation and circulation data

  3. Oxygen uptake efficiency slope and peak oxygen consumption predict prognosis in children with tetralogy of Fallot.

    Science.gov (United States)

    Tsai, Yun-Jeng; Li, Min-Hui; Tsai, Wan-Jung; Tuan, Sheng-Hui; Liao, Tin-Yun; Lin, Ko-Long

    2016-07-01

    Oxygen uptake efficiency slope (OUES) and peak oxygen consumption (VO2peak) are exercise parameters that can predict cardiac morbidity in patients with numerous heart diseases. But the predictive value in patients with tetralogy of Fallot is still undetermined, especially in children. We evaluated the prognostic value of OUES and VO2peak in children with total repair of tetralogy of Fallot. Retrospective cohort study. Forty tetralogy of Fallot patients younger than 12 years old were recruited. They underwent a cardiopulmonary exercise test during the follow-up period after total repair surgery. The results of the cardiopulmonary exercise test were used to predict the cardiac related hospitalization in the following two years after the test. OUES normalized by body surface area (OUES/BSA) and the percentage of predicted VO2peak appeared to be predictive for two-year cardiac related hospitalization. Receiver operating characteristic curve analysis demonstrated that the best threshold value for OUES/BSA was 1.029 (area under the curve = 0.70, p = 0.03), and for VO2peak was 74% of age prediction (area under the curve = 0.72, p = 0.02). The aforementioned findings were confirmed by Kaplan-Meier plots and log-rank test. OUES/BSA and VO2peak are useful predictors of cardiac-related hospitalization in children with total repair of tetralogy of Fallot. © The European Society of Cardiology 2015.

  4. Vastly Enhanced BiVO4 Photocatalytic OER Performance by NiCoO2 as Cocatalyst

    KAUST Repository

    Palaniselvam, Thangavelu; Shi, Le; Mettela, Gangaiah; Anjum, Dalavar H.; Li, Renyan; Katuri, Krishna; Saikaly, Pascal; Wang, Peng

    2017-01-01

    Here, a simple and efficient preparation of NiCoO nanoparticle modified nanoporous bismuth vanadate (BiVO) thin film and its application in photoelectrocatalytic (PEC) oxygen evolution reaction (OER) is demonstrated. The role of Ni

  5. Application of Electron Structure Calculations to the Migration of Oxygen through a Perovskite Membrane

    Science.gov (United States)

    Wood, Douglas A.

    The focus of this thesis is the application of electron structure calculations, particularly density functional theory, to the analysis of the process by which oxygen is able to migrate through a perovskite crystal. This property creates the possibility of using perovskite membranes to separate oxygen from air. This could be applied to the generation of syngas directly from natural gas without the need for a separate air separation unit. A perovskite has the nominal formula ABO3 where A is a rare earth type cation and B is a transition type cation. The structure consists of the B cations arranged in a cube with the A cation in the center. The oxygen ions are located at the midpoint of each B-B cube edge and form an octahedron centered on each B cation. Any real perovskite crystal will contain a certain fraction of vacancies at the oxygen sites. Oxygen migrates through the crystal by jumping from a neighboring site to the vacancy. The permeability of the crystal is thus a function of the concentration of vacancies and the activation energy of the jump from a neighboring site to the vacancy. These properties can be modified by adding dopants for the A and B cations. The literature contains a substantial amount of experimental work on the effect of such dopants. The overall migration process can be divided into components (i) the concentration of oxygen vacancies, (ii) the activation energy for a neighboring on-site oxygen atom to jump to the vacant site, (iii) the concentration of surface vacancies, and (iv) the processes by which oxygen ions transfer back and forth between the perovskite surface and the contiguous vapor space. Using SrTiO3 and LaCoO3 as model compounds, DFT calculations have been used to (i) calculate various properties of the perovskite crystal, (ii) estimate the activation energy of a jump between an occupied oxygen site and an adjacent vacant oxygen site, (iii) predict the effects of various dopants at the A and B site and (iv) analyze the

  6. HEART RATE VARIABILITY AND BODY COMPOSITION AS VO2MAX DETERMINANTS

    Directory of Open Access Journals (Sweden)

    Henry Humberto León-Ariza

    Full Text Available ABSTRACT Introduction: The maximum oxygen consumption (VO2max is the gold standard in the cardiorespiratory endurance assessment. Objective: This study aimed to develop a mathematical model that contains variables to determine the VO2max of sedentary people. Methods: Twenty participants (10 men and 10 women with a mean age of 19.8±1.77 years were included. For each participant, body composition (percentage of fat and muscle, heart rate variability (HRV at rest (supine and standing, and VO2max were evaluated through an indirect test on a cycloergometer. A multivariate linear regression model was developed from the data obtained, and the model assumptions were verified. Results: Using the data obtained, including percentage of fat (F, percentage of muscle (M, percentage of power at very low frequency (VLF, α-value of the detrended fluctuation analysis (DFAα1, heart rate (HR in the resting standing position, and age of the participants, a model was established for men, which was expressed as VO2max = 4.216 + (Age*0.153 + (F*0.110 - (M*0.053 - (VLF*0.649 - (DFAα1*2.441 - (HR*0.014, with R2 = 0.965 and standard error = 0.146 L/min. For women, the model was expressed as VO2max = 1.947 - (Age*0.047 + (F*0.024 + (M*0.054 + (VLF*1.949 - (DFAα1*0.424 - (HR*0.019, with R2 = 0.987 and standard error = 0.077 L/min. Conclusion: The obtained model demonstrated the influence exerted by body composition, the autonomic nervous system, and age in the prediction of VO2max.

  7. Electronic structure of vacancies and vacancy clusters in simple metals

    International Nuclear Information System (INIS)

    Manninen, M.; Nieminen, R.M.

    1978-05-01

    The self-consistent density functional approach has been applied in a study of electronic properties of vacancies and vacancy clusters in simple metals. The electron density profiles and potentials have been obtained for spherical voids of varying size. The formation energies and residual resistivities have been calculated for vacancies using both perturbational and variational inclusion of discrete lattice effects. The relation of the void properties to the plane surface ones is studied, and the inadequacy of the jellium-based methods to high-index faces is demonstrated. (author)

  8. A study on native defects and magnetic properties in undoped rutile TiO2 using LDA and LDA+UO p+UTi d methods

    Science.gov (United States)

    Shi, Li-Bin; Wang, Yong Ping

    2016-05-01

    The native defects and magnetic properties in undoped rutile TiO2 are studied using local density approximation (LDA) and LDA adding Hubbard parameters (U) schemes. The band gap is adjusted to experimental value of 3.0 eV by combination of UTi d=4.2 eV and UO p=4.8 eV. This LDA+U methodology overcomes the band-gap problem and renders the approach more predictive. The formation energies of oxygen vacancy (VO), oxygen interstitial (Oi), titanium vacancy (VTi), titanium interstitial (Tii), oxygen anti-sites (OTi), and titanium anti-sites (TiO) are investigated by the LDA and LDA+U methods. In addition, some ground state configurations can be obtained by optimization of total spin. It is found that native defects can induce spin polarization and produce magnetic moment.

  9. Current-induced metal-insulator transition in VO x thin film prepared by rapid-thermal-annealing

    International Nuclear Information System (INIS)

    Cho, Choong-Rae; Cho, SungIl; Vadim, Sidorkin; Jung, Ranju; Yoo, Inkyeong

    2006-01-01

    The phenomenon of metal-insulator transition (MIT) in polycrystalline VO x thin films and their preparations have been studied. The films were prepared by sputtering of vanadium thin films succeeded by Rapid Thermal Annealing (RTA) in oxygen ambient at 500 deg. C. Crystalline, compositional, and morphological characterizations reveal a continuous change of phase from vanadium metal to the highest oxide phase, V 2 O 5 , with the time of annealing. Electrical MIT switching has been observed in these films. Sweeping mode, electrode area, and temperature dependent MIT has been studied in Pt/VO x /Pt vertical structure. The important parameters for MIT in VO x have been found to be the current density and the electric field, which depend on carrier density in the films

  10. Vacancy-Mediated Magnetism in Pure Copper Oxide Nanoparticles

    Science.gov (United States)

    2010-01-01

    Room temperature ferromagnetism (RTF) is observed in pure copper oxide (CuO) nanoparticles which were prepared by precipitation method with the post-annealing in air without any ferromagnetic dopant. X-ray photoelectron spectroscopy (XPS) result indicates that the mixture valence states of Cu1+ and Cu2+ ions exist at the surface of the particles. Vacuum annealing enhances the ferromagnetism (FM) of CuO nanoparticles, while oxygen atmosphere annealing reduces it. The origin of FM is suggested to the oxygen vacancies at the surface/or interface of the particles. Such a ferromagnet without the presence of any transition metal could be a very good option for a class of spintronics. PMID:20671775

  11. Multiple variables explain the variability in the decrement in VO2max during acute hypobaric hypoxia.

    Science.gov (United States)

    Robergs, R A; Quintana, R; Parker, D L; Frankel, C C

    1998-06-01

    We used multiple regression analyses to determine the relationships between the decrement in sea level (SL, 760 Torr) VO2max during hypobaric hypoxia (HH) and variables that could alter or be related to the decrement in VO2max. HH conditions consisted of 682 Torr, 632 Torr, and 566 Torr, and the measured independent variables were SL-VO2max, SL lactate threshold (SL-LT), the change in hemoglobin saturation at VO2max between 760 and 566 Torr (delta SaO2max), lean body mass (LBM), and gender. Male (N = 14) and female (N = 14) subjects of varied fitness, training status, and residential altitude (1,640-2,460 m) completed cycle ergometry tests of VO2max at each HH condition under randomized and single-blinded conditions. VO2max decreased significantly from 760 Torr after 682 Torr (approximately 915 m) (3.5 +/- 0.9 to 3.4 +/- 0.8 L.min-1, P = 0.0003). Across all HH conditions, the slope of the relative decrement in VO2max (%VO2max) during HH was -9.2%/100 mm Hg (-8.1%/1000 m) with an initial decrease from 100% estimated to occur below 705 Torr (610 m). Step-wise multiple regression revealed that SL-VO2max, SL-LT, delta SaO2max, LBM, and gender each significantly combined to account for 89.03% of the variance in the decrement in VO2max (760-566 Torr) (P decrement in VO2max during HH. The unique variance explanation afforded by SL-LT, LBM, and gender suggests that issues pertaining to oxygen diffusion within skeletal muscle may add to the explanation of between subjects variability in the decrement in VO2max during HH.

  12. Low-level laser therapy improves the VO2 kinetics in competitive cyclists.

    Science.gov (United States)

    Lanferdini, Fábio J; Krüger, Renata L; Baroni, Bruno M; Lazzari, Caetano; Figueiredo, Pedro; Reischak-Oliveira, Alvaro; Vaz, Marco A

    2018-04-01

    Some evidence supports that low-level laser therapy (LLLT) reduces neuromuscular fatigue, so incrementing sports performance. A previous randomized controlled trial of our group showed increased exercise tolerance in male competitive cyclists treated with three different LLLT doses (3, 6, and 9 J/diode; or 135, 270, and 405 J/thigh) before time-to-exhaustion cycling tests. Now, the present study was designed to evaluate the effects of these LLLT doses on the VO 2 kinetics of athletes during cycling tests. Twenty male competitive cyclists (29 years) participated in a crossover, randomized, double-blind, and placebo-controlled trial. On the first day, the participants performed an incremental cycling test to exhaustion to determine maximal oxygen uptake (VO 2MAX ) and maximal power output (PO MAX ), as well as a familiarization with the time-to-exhaustion test. In the following days (2 to 5), all participants performed time-to-exhaustion tests at PO MAX . Before the exhaustion test, different doses of LLLT (3, 6, and 9 J/diode; or 135, 270, and 405 J/thigh, respectively) or placebo were applied bilaterally to the quadriceps muscle. All exhaustion tests were monitored online by an open-circuit spirometry system in order to analyze the VO 2 amplitude, VO 2 delay time, time constant (tau), and O 2 deficit. Tau and O 2 deficit were decreased with LLLT applications compared to the placebo condition (p  0.05) were found between the experimental conditions for VO 2 amplitude and VO 2 delay time. In conclusion, LLLT decreases tau and O 2 deficit during time-to-exhaustion tests in competitive cyclists, and these changes in VO 2 kinetics response can be one of the possible mechanisms to explain the ergogenic effect induced by LLLT.

  13. Diffusion of oxygen in uranium dioxide: A first-principles investigation

    International Nuclear Information System (INIS)

    Gupta, Florence; Brillant, Guillaume; Pasturel, Alain

    2010-01-01

    Results of ab initio density-functional theory calculations of the migration energies of oxygen vacancies and interstitials in stoichiometric UO 2 are reported. The diffusion of oxygen vacancies in UO 2 is found to be highly anisotropic, and the [1 0 0] direction is energetically favored. The atomic relaxations play an important role in reducing the migration barriers. Within the generalized gradient approximation (GGA), we find that the migration energies of the preferred vacancies and interstitials paths are, respectively, 1.18 and 1.09 eV. With the inclusion of the Hubbard U parameter to account for the 5f electron correlations in GGA+U, the vacancy migration energy is lowered to 1.01 eV while the interstitial migration energy increases slightly to 1.13 eV. We find, however, that the correlation effects have a drastic influence on the mechanism of interstitial migration through the stabilization of Willis-type clusters. Indeed, in contrast to GGA, in GGA+U there is an inversion of the migration path with the so-called 'saddle-point' position being lower in energy than the usual starting position. Thus while the migration barriers are nearly the same in GGA and GGA+U, the mechanisms are completely different. Our results clearly indicate that both vacancies and interstitials contribute almost equally to the diffusion of oxygen in UO 2 .

  14. Visible light driven photocatalysis and antibacterial activity of AgVO3 and Ag/AgVO3 nanowires

    International Nuclear Information System (INIS)

    Singh, Anamika; Dutta, Dimple P.; Ballal, A.; Tyagi, A.K.; Fulekar, M.H.

    2014-01-01

    Graphical abstract: - Highlights: • Ag/AgVO 3 and pure AgVO 3 nanowires synthesized by sonochemical process. • Characterization done using XRD, SEM, TEM, EDX and BET analysis. • Visible light degradation of RhB by Ag/AgVO 3 within 45 min. • Antibacterial activity of Ag/AgVO 3 demonstrated. - Abstract: Ag/AgVO 3 nanowires and AgVO 3 nanorods were synthesized in aqueous media via a facile sonochemical route. The as-synthesized products were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscopy together with an energy dispersion X-ray spectrum analysis, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The results revealed that inert atmosphere promotes the formation of Ag/AgVO 3 nanowires. The photocatalytic studies revealed that the Ag/AgVO 3 nanowires exhibited complete photocatalytic degradation of Rhodamine B within 45 min under visible light irradiation. The antibacterial activity of Ag/AgVO 3 nanowires was tested against Escherechia coli and Bacillus subtilis. The minimum growth inhibitory concentration value was found to be 50 and 10 folds lower than for the antibiotic ciprofloxacin for E. coli and B. subtilis, respectively. The antibacterial properties of the β-AgVO 3 nanorods prove that in case of the Ag dispersed Ag/AgVO 3 nanowires, the enhanced antibacterial action is also due to contribution from the AgVO 3 support

  15. Insight into the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response in chemically grown ZnO/Al2O3 films

    Science.gov (United States)

    Agrawal, Arpana; Saroj, Rajendra K.; Dar, Tanveer A.; Baraskar, Priyanka; Sen, Pratima; Dhar, Subhabrata

    2017-11-01

    We report the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response of ZnO films grown on a sapphire substrate at various oxygen flow rates using the chemical vapor deposition technique. The nonlinear refraction response was investigated in the off-resonant regime using a CW He-Ne laser source to examine the role of the intermediate bandgap states. It has been observed that the structural defects strongly influence the optical nonlinearity in the off-resonant regime. Nonlinearity has been found to improve as the oxygen flow rate is lowered from 2 sccm to 0.3 sccm. From photoluminescence studies, we observe that the enhanced defect density of the electronic defect levels due to the increased concentration of structural defects (with the decrease in the oxygen flow rate) is responsible for this improved optical nonlinearity along with the thermal effect. This suggests that defect engineering is an effective way to tailor the nonlinearity of ZnO films and their utility for optoelectronic device applications.

  16. Single crystal structures of the new vanadates CuMgVO{sub 4} and AgMgVO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Ben Yahia, Hamdi, E-mail: Hyahia@qf.org.qa [Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, PO Box 5825, Doha (Qatar); Shikano, Masahiro, E-mail: shikano.masahiro@aist.go.jp [Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Essehli, Rachid; Belharouak, Ilias [Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, PO Box 5825, Doha (Qatar)

    2016-08-01

    The new compounds CuMgVO{sub 4} and AgMgVO{sub 4} have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. CuMgVO{sub 4} crystallizes with Na{sub 2}CrO{sub 4}-type structure with space group Cmcm, a = 5.6932 (10), b = 8.7055 (15), c = 6.2789 (10) Å, V = 311.20 (9) Å{sup 3}, and Z = 4, whereas AgMgVO{sub 4} crystallizes in the maricite-type structure with space group Pnma, a = 9.4286 (14), b = 6.7465 (10), c = 5.3360 (8) Å, V = 339.42 (9) Å{sup 3}, and Z = 4. Both structures of CuMgVO{sub 4}, and AgMgVO{sub 4} contain MgO{sub 4} chains made up of edge-sharing MgO{sub 6} octahedra. In CuMgVO{sub 4} the MgO{sub 4} chains are interconnected through CuVO{sub 4} double chains made up of VO{sub 4} and CuO{sub 4} tetrahedra sharing corners and edges, however in AgMgVO{sub 4} the chains are interlinked by the VO{sub 4} and AgO{sub 4} tetrahedra sharing only corners. - Highlights: • We have been able to grow CuMgVO{sub 4} and AgMgVO{sub 4} single crystals. • We solved their crystal structures using single crystal data. • We compared the crystal structures of CuMgVO{sub 4} and AgMgVO{sub 4}.

  17. Is Recreational Soccer Effective for Improving VO2max A Systematic Review and Meta-Analysis.

    Science.gov (United States)

    Milanović, Zoran; Pantelić, Saša; Čović, Nedim; Sporiš, Goran; Krustrup, Peter

    2015-09-01

    Soccer is the most popular sport worldwide, with a long history and currently more than 500 million active participants, of whom 300 million are registered football club members. On the basis of scientific findings showing positive fitness and health effects of recreational soccer, FIFA (Fédération Internationale de Football Association) introduced the slogan "Playing football for 45 min twice a week-best prevention of non-communicable diseases" in 2010. The objective of this paper was to perform a systematic review and meta-analysis of the literature to determine the effects of recreational soccer on maximal oxygen uptake (VO2max). Six electronic databases (MEDLINE, PubMed, SPORTDiscus, Web of Science, CINAHL and Google Scholar) were searched for original research articles. A manual search was performed to cover the areas of recreational soccer, recreational physical activity, recreational small-sided games and VO2max using the following key terms, either singly or in combination: recreational small-sided games, recreational football, recreational soccer, street football, street soccer, effect, maximal oxygen uptake, peak oxygen uptake, cardiorespiratory fitness, VO2max. The inclusion criteria were divided into four sections: type of study, type of participants, type of interventions and type of outcome measures. Probabilistic magnitude-based inferences for meta-analysed effects were based on standardised thresholds for small, moderate and large changes (0.2, 0.6 and 1.2, respectively) derived from between-subject standard deviations for baseline fitness. Seventeen studies met the inclusion criteria and were included in the systematic review and meta-analysis. Mean differences showed that VO2max increased by 3.51 mL/kg/min (95 % CI 3.07-4.15) over a recreational soccer training programme in comparison with other training models. The meta-analysed effects of recreational soccer on VO2max compared with the controls of no exercise, continuous running and strength

  18. Promoted Fixation of Molecular Nitrogen with Surface Oxygen Vacancies on Plasmon-Enhanced TiO2 Photoelectrodes.

    Science.gov (United States)

    Li, Chengcheng; Wang, Tuo; Zhao, Zhi-Jian; Yang, Weimin; Li, Jian-Feng; Li, Ang; Yang, Zhilin; Ozin, Geoffrey A; Gong, Jinlong

    2018-02-19

    A hundred years on, the energy-intensive Haber-Bosch process continues to turn the N 2 in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The urgency of mitigating climate change motivates society to progress toward a more sustainable method for fixing N 2 that is based on clean energy. Surface oxygen vacancies (surface O vac ) hold great potential for N 2 adsorption and activation, but introducing O vac on the very surface without affecting bulk properties remains a great challenge. Fine tuning of the surface O vac by atomic layer deposition is described, forming a thin amorphous TiO 2 layer on plasmon-enhanced rutile TiO 2 /Au nanorods. Surface O vac in the outer amorphous TiO 2 thin layer promote the adsorption and activation of N 2 , which facilitates N 2 reduction to ammonia by excited electrons from ultraviolet-light-driven TiO 2 and visible-light-driven Au surface plasmons. The findings offer a new approach to N 2 photofixation under ambient conditions (that is, room temperature and atmospheric pressure). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Oxygen permeation modelling of perovskites

    NARCIS (Netherlands)

    van Hassel, Bart A.; van Hassel, B.A.; Kawada, Tatsuya; Sakai, Natsuko; Yokokawa, Harumi; Dokiya, Masayuki; Bouwmeester, Henricus J.M.

    1993-01-01

    A point defect model was used to describe the oxygen nonstoichiometry of the perovskites La0.75Sr0.25CrO3, La0.9Sr0.1FeO3, La0.9Sr0.1CoO3 and La0.8Sr0.2MnO3 as a function of the oxygen partial pressure. Form the oxygen vacancy concentration predicte by the point defect model, the ionic conductivity

  20. C=C bond cleavage on neutral VO3(V2O5)n clusters.

    Science.gov (United States)

    Dong, Feng; Heinbuch, Scott; Xie, Yan; Bernstein, Elliot R; Rocca, Jorge J; Wang, Zhe-Chen; Ding, Xun-Lei; He, Sheng-Gui

    2009-01-28

    The reactions of neutral vanadium oxide clusters with alkenes (ethylene, propylene, 1-butene, and 1,3-butadiene) are investigated by experiments and density function theory (DFT) calculations. Single photon ionization through extreme ultraviolet radiation (EUV, 46.9 nm, 26.5 eV) is used to detect neutral cluster distributions and reaction products. In the experiments, we observe products (V(2)O(5))(n)VO(2)CH(2), (V(2)O(5))(n)VO(2)C(2)H(4), (V(2)O(5))(n)VO(2)C(3)H(4), and (V(2)O(5))(n)VO(2)C(3)H(6), for neural V(m)O(n) clusters in reactions with C(2)H(4), C(3)H(6), C(4)H(6), and C(4)H(8), respectively. The observation of these products indicates that the C=C bonds of alkenes can be broken on neutral oxygen rich vanadium oxide clusters with the general structure VO(3)(V(2)O(5))(n=0,1,2...). DFT calculations demonstrate that the reaction VO(3) + C(3)H(6) --> VO(2)C(2)H(4) + H(2)CO is thermodynamically favorable and overall barrierless at room temperature. They also provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes is broken on VO(3)(V(2)O(5))(n=0,1,2...) clusters. A catalytic cycle for alkene oxidation on vanadium oxide is suggested based on our experimental and theoretical investigations. The reactions of V(m)O(n) with C(6)H(6) and C(2)F(4) are also investigated by experiments. The products VO(2)(V(2)O(5))(n)C(6)H(4) are observed for dehydration reactions between V(m)O(n) clusters and C(6)H(6). No product is detected for V(m)O(n) clusters reacting with C(2)F(4). The mechanisms of the reactions between VO(3) and C(2)F(4)/C(6)H(6) are also investigated by calculations at the B3LYP/TZVP level.

  1. Gevaar VoIP voor telecomsector overdreven

    NARCIS (Netherlands)

    Deventer, M.O. van; Wegberg, M. van

    2004-01-01

    Het is een hype Voice-over-IP (VoIP) voor te stellen als een ontwrichtende technologie die de telecomindustrie ingrijpend zal veranderen. Maar hoe ontwrichtend is VoIP eigenlijk? Oskar van Deventer en Marc van Wegberg analyseren drie vormen van VoIP en laten zien dat alleen ‘VoIP-chat’ potentieel

  2. A comprehensive investigation of tetragonal Gd-doped BiVO{sub 4} with enhanced photocatalytic performance under sun-light

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Yangyang; Tan, Guoqiang, E-mail: tan3114@163.com; Dong, Guohua; Ren, Huijun; Xia, Ao

    2016-02-28

    Graphical abstract: - Highlights: • Tetragonal Gd-BiVO{sub 4} with enhanced photocatalytic activity was synthesized. • Gd doping can induce the phase transition from monoclinic to tetragonal BiVO{sub 4}. • GdVO{sub 4} seeds as crystal nucleus dominate the formation of tetragonal Gd-BiVO{sub 4}. • Tetragonal Gd-BiVO{sub 4} exhibits the excellent separation of electrons and holes. • The contribution of high photocatalytic activity under sun-light is from UV-light. - Abstract: Tetragonal Gd-doped BiVO{sub 4} having enhanced photocatalytic activity have been synthesized by a facile microwave hydrothermal method. The structural analysis indicates that Gd doping can induce the phase transition from monoclinic to tetragonal BiVO{sub 4}. The reaction results in precursor solutions imply that tetragonal GdVO{sub 4} seeds as crystal nucleus are the original and determined incentives to force the formation of tetragonal Gd-BiVO{sub 4}. The influences of the surface defect, band structure, and BET surface area on the improved photocatalytic activities of tetragonal Gd-doped BiVO{sub 4} are investigated systematically. The results demonstrate that the more surface oxygen deficiencies as active sites and the excellent mobility and separation of photogenerated electrons and holes are beneficial to the enhancement of the photocatalytic performance of tetragonal Gd-BiVO{sub 4}. The RhB photodegradation experiments indicate that the contribution of high photocatalytic activities under simulated sun-light is mainly from UV-light region due to the tetragonal structure feature. The best photocatalytic performance is obtained for tetragonal 10 at% Gd-BiVO{sub 4}, of which the RhB degradation rate can reach to 96% after 120 min simulated sun-light irradiation. The stable tetragonal Gd-BiVO{sub 4} with efficient mineralization will be a promising photocatalytic material applied in water purification.

  3. Critical evaluation of oxygen-uptake assessment in swimming.

    Science.gov (United States)

    Sousa, Ana; Figueiredo, Pedro; Pendergast, David; Kjendlie, Per-Ludvik; Vilas-Boas, João P; Fernandes, Ricardo J

    2014-03-01

    Swimming has become an important area of sport science research since the 1970s, with the bioenergetic factors assuming a fundamental performance-influencing role. The purpose of this study was to conduct a critical evaluation of the literature concerning oxygen-uptake (VO2) assessment in swimming, by describing the equipment and methods used and emphasizing the recent works conducted in ecological conditions. Particularly in swimming, due to the inherent technical constraints imposed by swimming in a water environment, assessment of VO2max was not accomplished until the 1960s. Later, the development of automated portable measurement devices allowed VO2max to be assessed more easily, even in ecological swimming conditions, but few studies have been conducted in swimming-pool conditions with portable breath-by-breath telemetric systems. An inverse relationship exists between the velocity corresponding to VO2max and the time a swimmer can sustain it at this velocity. The energy cost of swimming varies according to its association with velocity variability. As, in the end, the supply of oxygen (whose limitation may be due to central-O2 delivery and transportation to the working muscles-or peripheral factors-O2 diffusion and utilization in the muscles) is one of the critical factors that determine swimming performance, VO2 kinetics and its maximal values are critical in understanding swimmers' behavior in competition and to develop efficient training programs.

  4. Chemisorption of oxygen and subsequent reactions on low index surfaces of β-Mo2C

    DEFF Research Database (Denmark)

    Shi, Xue Rong; Wang, Shengguang; Wang, Jianguo

    2016-01-01

    to the carbon vacancy were identified. We examined the effect of oxygen coverage on the morphology of β-Mo2C by plotting the equilibrium crystal shape. Thermodynamic effect of temperature and reactant or product pressure on the CO/CO2 desorption were investigated. The CO/CO2 desorption is more favorable...... at the saturated oxygen coverage than the low oxygen coverage thermodynamically. The subsequent oxygen diffusion to the carbon vacancy after CO/CO2 desorption may happen depending on the surfaces and oxygen coverage....

  5. Effects of Hemopure on maximal oxygen uptake and endurance performance in healthy humans.

    Science.gov (United States)

    Ashenden, M J; Schumacher, Y O; Sharpe, K; Varlet-Marie, E; Audran, M

    2007-05-01

    Haemoglobin-based oxygen carriers (HBOCs) such as Hemopure are touted as a tenable substitute for red blood cells and therefore potential doping agents, although the mechanisms of oxygen transport of HBOCs are incompletely understood. We investigated whether infusion of Hemopure increased maximal oxygen uptake (V.O 2max) and endurance performance in healthy subjects. Twelve male subjects performed two 4-minute submaximal exercise bouts equivalent to 60 % and 75 % of V.O (2max) on a cycle ergometer, followed by a ramped incremental protocol to elicit V.O (2max). A crossover design tested the effect of infusing either 30 g (6 subjects) or 45 g (6 subjects) of Hemopure versus a placebo. Under our study conditions, Hemopure did not increase V.O (2max) nor endurance performance. However, the infusion of Hemopure caused a decrease in heart rate of approximately 10 bpm (p=0.009) and an average increase in mean ( approximately 7 mmHg) and diastolic blood pressure ( approximately 8 mmHg) (p=0.046) at submaximal and maximal exercise intensities. Infusion of Hemopure did not bestow the same physiological advantages generally associated with infusion of red blood cells. It is conceivable that under exercise conditions, the hypertensive effects of Hemopure counter the performance-enhancing effect of improved blood oxygen carrying capacity.

  6. Facile synthesis and high activity of novel BiVO{sub 4}/FeVO{sub 4} heterojunction photocatalyst for degradation of metronidazole

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jinhai [State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023 (China); School of Chemical Engineering, Guizhou University of Engineering Science, Bijie 551700 (China); Zhao, Wei; Guo, Yang; Wei, Zhongbo; Han, Mengshu [State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023 (China); He, Huan [State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023 (China); School of Public Health, University of Illinois at Chicago, Chicago, IL 60631 (United States); Yang, Shaogui [State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023 (China); Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824 (United States); Sun, Cheng, E-mail: envidean@nju.edu.cn [State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023 (China)

    2015-10-01

    Graphical abstract: - Highlights: • BiVO{sub 4}/FeVO{sub 4} was synthesized by a facile one-step hydrothermal method. • BiVO{sub 4}/FeVO{sub 4} displays superior photocatalytic activity. • The photocatalytic mechanism were discussed in detail. - Abstract: The novel BiVO{sub 4}/FeVO{sub 4} heterojunction photocatalyst was successfully synthesized by a facile hydrothermal method firstly. The physical and chemical properties of as-prepared samples were characterized based upon XRD, XPS, BET, SEM, EDS, TEM, UV–vis DRS and fluorescence spectrum techniques. The TEM images showed a clear interface between BiVO{sub 4} and FeVO{sub 4}, indicating that a heterojunction between BiVO{sub 4} and FeVO{sub 4} was formed during the hydrothermal reaction. In addition, the photodegradation activity of metronidazole (MNZ) was used as a measurement for photocatalytic performance of BiVO{sub 4}, FeVO{sub 4} and BiVO{sub 4}/FeVO{sub 4} heterojunction photocatalyst. It indicated that under visible light irradiation the photocatalytic activity of BiVO{sub 4}/FeVO{sub 4} heterojunction photocatalyst was very effective, and moreover, much higher than the single BiVO{sub 4} or single FeVO{sub 4}. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation of the electronic structure, and the experimental results.

  7. Crystal structure of ferroelectric Bi{sub 2}VO{sub 5.5}

    Energy Technology Data Exchange (ETDEWEB)

    Sooryanarayana, K.; Guru Row, T.N.; Varma, K.B.R. [Indian Inst. of Science, Bangalore (India)

    1997-12-01

    The structure of the {alpha}-phase of bismuth vanadate Bi{sub 2}VO{sub 5.5} has been determined using single crystal X-ray diffraction data in the space group Aba2. The refinement involves a well defined disorder at the vanadium site, which incorporates the features of the superlattice structure with vanadium tetrahedra and oxygen-deficient octahedra that is displaced about the twofold axis.

  8. VoIP Accessibility: A Usability Study of Voice over Internet Protocol (VoIP) Systems and A Survey of VoIP Users with Vision Loss

    Science.gov (United States)

    Packer, Jaclyn; Reuschel, William

    2018-01-01

    Introduction: Accessibility of Voice over Internet Protocol (VoIP) systems was tested with a hands-on usability study and an online survey of VoIP users who are visually impaired. The survey examined the importance of common VoIP features, and both methods assessed difficulty in using those features. Methods: The usability test included four paid…

  9. A COMPARISON BETWEEN VENTILATION AND HEART RATE AS INDICATOR OF OXYGEN UPTAKE DURING DIFFERENT INTENSITIES OF EXERCISE

    Directory of Open Access Journals (Sweden)

    Jacques Prioux

    2010-03-01

    Full Text Available The aim of this study is to compare the relation between ventilation (VE and oxygen uptake (VO2 [VO2=ƒ(VE] and between heart rate (HR and VO2 [VO2=ƒ(HR]. Each one of the subjects performed three types of activities of different intensities (walking without load, walking with load and intermittent work. VO2, VE, and HR were measured continuously by using indirect calorimetry and an electrocardiogram. Linear regressions and coefficients of determination (r² were calculated to compare the relation VO2 =ƒ(VE and VO2 =ƒ(HR for two different regroupings: by session duration (r²session and by subject (r²subject. Results showed that r²session of the relation VO2 =ƒ(VE were significantly higher than those of the relation VO2 =ƒ(HR for steady state activities (walking with or without load during 3 or 6 min, p < 0.01 and for activities without oxygen consumption steady state (walking with or without load during 1 min, p < 0.01 and intermittent work, p < 0.05. VE is more strongly correlated with VO2 than with HR. This is a very promising approach to develop a new method to estimate energy expenditure

  10. Radiation-induced defects in LiAlO{sub 2} crystals: Holes trapped by lithium vacancies and their role in thermoluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Holston, M.S.; McClory, J.W.; Giles, N.C. [Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433 (United States); Halliburton, L.E., E-mail: Larry.Halliburton@mail.wvu.edu [Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506 (United States)

    2015-04-15

    Electron paramagnetic resonance (EPR) is used to identify the primary hole trap in undoped lithium aluminate (LiAlO{sub 2}) crystals. Our interest in this material arises because it is a candidate for radiation detection applications involving either optically stimulated luminescence (OSL) or thermoluminescence (TL). During an x-ray irradiation at room temperature, holes are trapped at oxygen ions adjacent to lithium vacancies. Large concentrations of these lithium vacancies are introduced into the crystal during growth. With the magnetic field along the [001] direction, the EPR spectrum from these trapped-hole centers consists of eleven lines, evenly spaced but with varying intensities, caused by nearly equal hyperfine interactions with two {sup 27}Al nuclei (I=5/2, 100% abundant). The g matrix is determined from the angular dependence of the EPR spectrum and has principal values of 2.0130, 2.0675, and 2.0015. These g shifts strongly support the model of a hole in a p orbital on an oxygen ion. The adjacent lithium vacancy stabilizes the hole on the oxygen ion. A sequence of pulsed thermal anneals above room temperature shows that the EPR spectrum from the holes trapped adjacent to the lithium vacancies disappears in the 90–120 °C range. The thermal decay of these hole centers directly correlates with an intense TL peak near 105 °C. Signals at lower magnetic field in the 9.4 GHz EPR spectra suggest that the electron trap associated with this TL peak at 105 °C may be a transition-metal-ion impurity, most likely Fe, located at a cation site. Additional less intense TL peaks are observed near 138, 176, and 278 °C. - Highlights: • Undoped LiAlO{sub 2} crystals are irradiated at room temperature with x-rays. • EPR is used to identify holes trapped at oxygen ions adjacent to lithium vacancies. • Thermal decay of the EPR spectrum correlates with an intense TL peak at 105 °C.

  11. Memristive behaviour of Si-Al oxynitride thin films: the role of oxygen and nitrogen vacancies in the electroforming process

    Science.gov (United States)

    Blázquez, O.; Martín, G.; Camps, I.; Mariscal, A.; López-Vidrier, J.; Ramírez, J. M.; Hernández, S.; Estradé, S.; Peiró, F.; Serna, R.; Garrido, B.

    2018-06-01

    The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole‑Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching.

  12. Magnetoresistance Versus Oxygen Deficiency in Epi-stabilized SrRu1 - x Fe x O3 - δ Thin Films.

    Science.gov (United States)

    Dash, Umasankar; Acharya, Susant Kumar; Lee, Bo Wha; Jung, Chang Uk

    2017-12-01

    Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxide materials. Here, we studied the influence of oxygen vacancies on the magnetoresistance (MR) properties of SrRu 1 - x Fe x O 3 - δ epitaxial thin films (x = 0.10, 0.20, and 0.30). For this purpose, we synthesized highly strained epitaxial SrRu 1 - x Fe x O 3 - δ thin films with atomically flat surfaces containing different amounts of oxygen vacancies using pulsed laser deposition. Without an applied magnetic field, the films with x = 0.10 and 0.20 showed a metal-insulator transition, while the x = 0.30 thin film showed insulating behavior over the entire temperature range of 2-300 K. Both Fe doping and the concentration of oxygen vacancies had large effects on the negative MR contributions. For the low Fe doping case of x = 0.10, in which both films exhibited metallic behavior, MR was more prominent in the film with fewer oxygen vacancies or equivalently a more metallic film. For semiconducting films, higher MR was observed for more semiconducting films having more oxygen vacancies. A relatively large negative MR (~36.4%) was observed for the x = 0.30 thin film with a high concentration of oxygen vacancies (δ = 0.12). The obtained results were compared with MR studies for a polycrystal of (Sr 1 - x La x )(Ru 1 - x Fe x )O 3 . These results highlight the crucial role of oxygen stoichiometry in determining the magneto-transport properties in SrRu 1 - x Fe x O 3 - δ thin films.

  13. Synthesis of surface oxygen-deficient BiPO{sub 4} nanocubes with enhanced visible light induced photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Bingtao; Yin, Haoyong; Li, Tao; Gong, Jianying; Lv, Shumei; Nie, Qiulin, E-mail: yhy@hdu.edu.cn [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou (China)

    2017-05-15

    The visible light driven BiPO{sub 4} nanocubes with sufficient surface oxygen deficiency were fabricated by a hydrothermal process and subsequently ultrasonic assistant Fe reduction process. The products were characterized by XRD, DRS, XPS, SEM and TEM which showed that the BiPO{sub 4} had cuboid-like shape with a smooth surface and clear edges and the oxygen vacancies were successfully introduced on the surface of the BiPO{sub 4} nanocubes. The as prepared oxygen-deficient BiPO{sub 4} nanocubes showed greatly enhanced visible light induced photocatalytic activity in degradation of Rhodamine B. The enhanced photocatalytic performance and expanded visible light response of BiPO{sub 4} may be due to the introduction of surface oxygen vacancies which can generate the oxygen vacancies mid-gap states lower to the conduction band of BiPO{sub 4}. (author)

  14. Higher Precision of Heart Rate Compared with VO2 to Predict Exercise Intensity in Endurance-Trained Runners.

    Science.gov (United States)

    Reis, Victor M; den Tillaar, Roland Van; Marques, Mario C

    2011-01-01

    The aim of the present study was to assess the precision of oxygen uptake with heart rate regression during track running in highly-trained runners. Twelve national and international level male long-distance road runners (age 30.7 ± 5.5 yrs, height 1.71 ± 0.04 m and mass 61.2 ± 5.8 kg) with a personal best on the half marathon of 62 min 37 s ± 1 min 22 s participated in the study. Each participant performed, in an all-weather synthetic track five, six min bouts at constant velocity with each bout at an increased running velocity. The starting velocity was 3.33 m·s(-1) with a 0.56 m·s(-1) increase on each subsequent bout. VO2 and heart rate were measured during the runs and blood lactate was assessed immediately after each run. Mean peak VO2 and mean peak heart rate were, respectively, 76.2 ± 9.7 mL·kg(-1)·min(-1) and 181 ± 13 beats·min(-1). The linearity of the regressions between heart rate, running velocity and VO2 were all very high (r > 0.99) with small standard errors of regression (i.e. Sy.x at the velocity associated with the 2 and 4 mmol·L(-1) lactate thresholds). The strong relationships between heart rate, running velocity and VO2 found in this study show that, in highly trained runners, it is possible to have heart rate as an accurate indicator of energy demand and of the running speed. Therefore, in this subject cohort it may be unnecessary to use VO2 to track changes in the subjects' running economy during training periods. Key pointsHeart rate is used in the control of exercise intensity in endurance sports.However, few studies have quantified the precision of its relationship with oxygen uptake in highly trained runners.We evaluated twelve elite half-marathon runners during track running at various intensities and established three regressions: oxygen uptake / heart rate; heart rate / running velocity and oxygen uptake / running velocity.The three regressions presented, respectively, imprecision of 4,2%, 2,75% and 4,5% at the velocity

  15. Integrating existing software toolkits into VO system

    Science.gov (United States)

    Cui, Chenzhou; Zhao, Yong-Heng; Wang, Xiaoqian; Sang, Jian; Luo, Ze

    2004-09-01

    Virtual Observatory (VO) is a collection of interoperating data archives and software tools. Taking advantages of the latest information technologies, it aims to provide a data-intensively online research environment for astronomers all around the world. A large number of high-qualified astronomical software packages and libraries are powerful and easy of use, and have been widely used by astronomers for many years. Integrating those toolkits into the VO system is a necessary and important task for the VO developers. VO architecture greatly depends on Grid and Web services, consequently the general VO integration route is "Java Ready - Grid Ready - VO Ready". In the paper, we discuss the importance of VO integration for existing toolkits and discuss the possible solutions. We introduce two efforts in the field from China-VO project, "gImageMagick" and "Galactic abundance gradients statistical research under grid environment". We also discuss what additional work should be done to convert Grid service to VO service.

  16. Origin and enhancement of spin polarized current in diluted magnetic oxides by oxygen vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Chou, Hsiung, E-mail: hchou@mail.nsysu.edu.tw; Yang, Kung-Shang; Tsao, Yao-Chung; Dwivedi, G. D.; Lin, Cheng-Pang [Department of Physics, National Sun Yat-Sen University, 70, Lienhai Road, Gushan District, Kaohsiung 804, Taiwan (China); Sun, Shih-Jye [Department of Applied Physics, National Kaohsiung University, 700, Gaoxiongdaxue Rd., Nanzi District, Kaohsiung 811, Taiwan (China); Lin, L. K.; Lee, S. F. [Institute of Physics, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115, Taiwan (China)

    2016-04-04

    Spin polarized current (SPC) is a crucial characteristic of diluted magnetic oxides due to the potential application of oxides in spintronic devices. However, most research has been focused on ferromagnetic properties rather than polarization of electric current, because direct measurements are difficult and the origin of SPC has yet to be fully understood. The method to increase the SPC percentage is beyond practical consideration at present. To address this problem, we focus on the role of oxygen vacancies (V{sub O}) on SPC, which are controlled by growing the Co-doped ZnO thin-films at room temperature in a reducing atmosphere [Ar + (1%–30%)H{sub 2}]. We found that the conductivity increases with an increase of V{sub O} via two independent channels: the variable range hopping (VRH) within localized states and the itinerant transport in the conduction band. The point contact Andreev reflection measurements at 4.2 K, where the electric conduction is governed only by the VRH mechanism, prove that the current flowing in the VRH hopping channel is SPC. The percentage of SPC increases with the introduction of V{sub O} and increase in its concentration. The transport measurement shows that by manipulating V{sub O}, one can control the percentage of VRH hopping conduction such that it can even dominate room temperature conduction. The highest achieved SPC ratio at room temperature was 80%.

  17. Lattice relaxation and ferromagnetic character of (LaVO3)m/SrVO3 superlattices

    KAUST Repository

    Schuster, Cosima B.

    2013-08-01

    The experimental observation that vanadate superlattices (LaVO 3)m/SrVO3 show ferromagnetism up to room temperature (Lüders U. et al., Phys. Rev. B, 80 (2009) 241102(R)) is investigated by means of density functional theory, and the band structure for m = 5 and 6 is calculated. A buckling of the interface VO2 layers is found in both cases, but subtle differences in bond length lead to very different properties for even and odd values of m: in the even case, the two interface VO2 layers effectively decouple from the adjacent LaO layers due to a strong bond length enhancement. This results into a local inversion of the orbital occupancy and to the confinement of the charge carriers. In the odd case, the amplitude of the bond length variation is smaller, so that the charge carriers spill into the deeper-lying VO2 layers, and spin-polarised interfaces are obtained. © Copyright EPLA, 2013.

  18. Observation of reduced phase transition temperature in N-doped thermochromic film of monoclinic VO_2

    International Nuclear Information System (INIS)

    Wan, Meinan; Xiong, Mo; Li, Neng; Liu, Baoshun; Wang, Shuo; Ching, Wai-Yim; Zhao, Xiujian

    2017-01-01

    Highlights: • N-doped VO_2(M1) thin films have been synthesized by annealing in NH_3 atmosphere. • The phase purity, microstructure and optical property of VO_2 thin film can be regulated by NH_3 concentration. • First-principles calculations have been carried out to study the mechanism of N-doping on energy band structures of VO_2(M1). • The energy band gaps of VO_2(M1) are tuned by substitution N-doping or interstitial N-doping. - Abstract: Research on monoclinic (M1) phase of VO_2 has attracted a great of interest for smart coating applications due to its exceptional thermochromic property. Herein, we report the results using a novel approach to synthesize N-doped VO_2(M1) thin films with high purity by heat treatment in NH_3 atmosphere. The N dopant in the film can be regulated by varying NH_3 concentration during the annealing process. We find that the N atoms are located at the interstitial sites or substitute oxygen atoms, and the V-N bonds in the VO_2 thin films increase with NH_3 concentration. The metal to insulator transition (MIT) temperature (τ_c_,_h) of the VO_2 thin film is effectively reduced from 80.0 to 62.9 °C, while the solar modulation efficiency (ΔT_s_o_l) and the modulation efficiency at 2000 nm (ΔT_2_0_0_0_n_m) are 7.36% and 55.6% respectively. The band gap of N-doped VO_2 thin films related to MIT (E_g_1) is estimated to be as low as 0.18–0.25 eV whereas the band gap associated with the visible transparency (E_g_2) is about 1.50–1.58 eV. Based on the highly accurate first-principles calculations, the E_g_1 of VO_2 (M1) is reduced after substituted or interstitial N-doping, while the E_g_2 alters with the mode of N-doping, which is excellent agreement with experimental measurement.

  19. Positron annihilation studies on the behaviour of vacancies in LaAlO3/SrTiO3 heterostructures

    Science.gov (United States)

    Yuan, Guoliang; Li, Chen; Yin, Jiang; Liu, Zhiguo; Wu, Di; Uedono, Akira

    2012-11-01

    The formation and diffusion of vacancies are studied in LaAlO3/SrTiO3 heterostructures. Oxygen vacancies (VOS) appear easily in the SrTiO3 substrate during LaAlO3 film growth at 700 °C and 10-4 Pa oxygen pressure rather than at 10-3-10-1 Pa, thus the latter two-dimensional electron gas should come from the polarity discontinuity at the (LaO)+/(TiO2)0 interface. For SrTiO3-δ/LaAlO3/SrTiO3, high-density VOS of the SrTiO3-δ film can pass through the LaAlO3 film and then diffuse to 1.7 µm depth in the SrTiO3 substrate, suggesting that LaAlO3 has VOS at its middle-deep energy levels within the band gap. Moreover, high-density VOS may combine with a strontium/titanium vacancy (VSr/Ti) to form VSr/Ti-O complexes in the SrTiO3 substrate at 700 °C.

  20. Effect of limb cooling on peripheral and global oxygen consumption in neonates.

    Science.gov (United States)

    Hassan, I A-A; Wickramasinghe, Y A; Spencer, S A

    2003-03-01

    To evaluate peripheral oxygen consumption (VO(2)) measurements using near infrared spectroscopy (NIRS) with arterial occlusion in healthy term neonates by studying the effect of limb cooling on peripheral and global VO(2). Twenty two healthy term neonates were studied. Peripheral VO(2) was measured by NIRS using arterial occlusion and measurement of the oxyhaemoglobin (HbO(2)) decrement slope. Global VO(2) was measured by open circuit calorimetry. Global and peripheral VO(2) was measured in each neonate before and after limb cooling. In 10 neonates, a fall in forearm temperature of 2.2 degrees C (mild cooling) decreased forearm VO(2) by 19.6% (p forearm temperature of 4 degrees C (moderate cooling) decreased forearm VO(2) by 34.7% (p cooling. The changes are more pronounced with moderate limb cooling when a concomitant rise in global VO(2) is observed. Change in peripheral temperature must be taken into consideration in the interpretation of peripheral VO(2) measurements in neonates.

  1. Thermodynamic, electronic, and magnetic properties of intrinsic vacancy defects in antiperovskite Ca3SnO

    Science.gov (United States)

    Batool, Javaria; Alay-e-Abbas, Syed Muhammad; Amin, Nasir

    2018-04-01

    The density functional theory based total energy calculations are performed to examine the effect of charge neutral and fully charged intrinsic vacancy defects on the thermodynamic, electronic, and magnetic properties of Ca3SnO antiperovskite. The chemical stability of Ca3SnO is evaluated with respect to binary compounds CaO, CaSn, and Ca2Sn, and the limits of atomic chemical potentials of Ca, Sn, and O atoms for stable synthesis of Ca3SnO are determined within the generalized gradient approximation parametrization scheme. The electronic properties of the pristine and the non-stoichiometric forms of this compound have been explored and the influence of isolated intrinsic vacancy defects (Ca, Sn, and O) on the structural, bonding, and electronic properties of non-stoichiometric Ca3SnO are analyzed. We also predict the possibility of achieving stable ferromagnetism in non-stoichiometric Ca3SnO by means of charge neutral tin vacancies. From the calculated total energies and the valid ranges of atomic chemical potentials, the formation energetics of intrinsic vacancy defects in Ca3SnO are evaluated for various growth conditions. Our results indicate that the fully charged calcium vacancies are thermodynamically stable under the permissible Sn-rich condition of stable synthesis of Ca3SnO, while tin and oxygen vacancies are found to be stable under the extreme Ca-rich condition.

  2. Ab initio atomic thermodynamics investigation on oxygen defects in the anatase TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Zhijun [College of Science, University of Shanghai for Science and Technology, Shanghai 200093 (China); Liu, Tingyu, E-mail: liutyyxj@163.com [College of Science, University of Shanghai for Science and Technology, Shanghai 200093 (China); Yang, Chenxing; Gan, Haixiu [College of Science, University of Shanghai for Science and Technology, Shanghai 200093 (China); Chen, Jianyu [Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhang, Feiwu [Nanochemistry Research Institute, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia)

    2013-01-05

    Highlights: Black-Right-Pointing-Pointer Three typical oxygen defects under the different annealing conditions have been studied. Black-Right-Pointing-Pointer The oxygen vacancy is easier to form at the surface than in the bulk. Black-Right-Pointing-Pointer The adsorption of O{sub 2} whose orientation is parallel to the surface should be more favorable. Black-Right-Pointing-Pointer The reduction reaction may firstly undertake at the surface during the annealing treatment. Black-Right-Pointing-Pointer The interstitial oxygen has important contribution to lead to the reduction of the band gap. - Abstract: In the framework of the ab initio atomic thermodynamics, the preliminary analysis of the oxygen defects in anatase TiO{sub 2} has been done by investigating the influence of the annealing treatment under representative conditions on three typical oxygen defects, that is, oxygen vacancy, oxygen adsorption and oxygen interstitial. Our results in this study agree well with the related experimental results. The molecular species of the adsorbed O{sub 2} is subject to the ratio of the number of the O{sub 2} to that of the vacancy, as well as to the initial orientation of O{sub 2} relative to the surface (101). Whatever the annealing condition is, the oxygen vacancy is easier to form at the surface than in the bulk indicating that the reduction reaction may firstly undertake at the surface during the annealing treatment, which is consistent with the phase transformation experiments. The molecular ion, peroxide species, caused by the interstitial oxygen has important contribution to the top of the valence band and lead to the reduction of the band gap.

  3. Estimated VO2max and its corresponding velocity predict performance of amateur runners

    Directory of Open Access Journals (Sweden)

    Bruno Ribeiro Ramalho Oliveira

    2012-03-01

    Full Text Available In recent years, there has been a substantial increase in the number of runners, with a proportional increase in their involvement in amateur street competition. Identification of the determinants of performance in this population appears necessary for optimization of time devoted to training. The objective of this study was to ascertain the association between estimated maximal oxygen uptake (VO2max, critical velocity (CV and VO2max velocity (VVO2max and athletic performance in the 3.6 km (uphill and 10 and 21.1 km (flatland events. Twelve amateur runners (nine male, mean age 36 ± 5 years underwent five tests: 1 and 5 km race on level ground, 3.6 km race with slope (≈8%, and indirect VO2max measurement. CV was determined from the linear relationship between distance and run time on the first two tests. The subjects then took part in two official 10 km and 21.1 km (half marathon races. VVO2max was calculated from the VO2max through a metabolic equation. VO2max showed the best association with running performance in the 10 and 21.1 km events. For the uphill race, VVO2max showed a better association. Overall, the variable with the highest average association was VO2max (0.91±0.07, followed by VVO2max (0.90±0.04 and VC (0.87±0.06. This study showed strong associations between physiological variables established by low-cost, user-friendly indirect methods and running performance in the 10 and 21.1 km (flatland and 3.6 km (uphill running events.

  4. Visible light driven photocatalysis and antibacterial activity of AgVO{sub 3} and Ag/AgVO{sub 3} nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Anamika [Department of Life Sciences, University of Mumbai, Santacruz (E), Mumbai 400 098 (India); Dutta, Dimple P., E-mail: dimpled@barc.gov.in [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Ballal, A. [Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Tyagi, A.K. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Fulekar, M.H. [School of Environment and Sustainable Development, Central University of Gujarat, Gandhinagar 382 030, Gujarat (India)

    2014-03-01

    Graphical abstract: - Highlights: • Ag/AgVO{sub 3} and pure AgVO{sub 3} nanowires synthesized by sonochemical process. • Characterization done using XRD, SEM, TEM, EDX and BET analysis. • Visible light degradation of RhB by Ag/AgVO{sub 3} within 45 min. • Antibacterial activity of Ag/AgVO{sub 3} demonstrated. - Abstract: Ag/AgVO{sub 3} nanowires and AgVO{sub 3} nanorods were synthesized in aqueous media via a facile sonochemical route. The as-synthesized products were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscopy together with an energy dispersion X-ray spectrum analysis, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The results revealed that inert atmosphere promotes the formation of Ag/AgVO{sub 3} nanowires. The photocatalytic studies revealed that the Ag/AgVO{sub 3} nanowires exhibited complete photocatalytic degradation of Rhodamine B within 45 min under visible light irradiation. The antibacterial activity of Ag/AgVO{sub 3} nanowires was tested against Escherechia coli and Bacillus subtilis. The minimum growth inhibitory concentration value was found to be 50 and 10 folds lower than for the antibiotic ciprofloxacin for E. coli and B. subtilis, respectively. The antibacterial properties of the β-AgVO{sub 3} nanorods prove that in case of the Ag dispersed Ag/AgVO{sub 3} nanowires, the enhanced antibacterial action is also due to contribution from the AgVO{sub 3} support.

  5. Ordering of vacancies on Si(001)

    NARCIS (Netherlands)

    Zandvliet, Henricus J.W.

    1997-01-01

    Missing dimer vacancies are always present on the clean Si(001) surface. The vacancy density can be increased by ion bombardment (Xe+, Ar+), etching (O2, Br2, I2, etc.) or Ni contamination. The equilibrium shape at low vacancy concentrations (<0.2¿0.3 monolayers) of these vacancy islands is

  6. VO for Education: Archive Prototype

    Science.gov (United States)

    Ramella, M.; Iafrate, G.; De Marco, M.; Molinaro, M.; Knapic, C.; Smareglia, R.; Cepparo, F.

    2014-05-01

    The number of remote control telescopes dedicated to education is increasing in many countries, leading to correspondingly larger and larger amount of stored educational data that are usually available only to local observers. Here we present the project for a new infrastructure that will allow teachers using educational telescopes to archive their data and easily publish them within the Virtual Observatory (VO) avoiding the complexity of professional tools. Students and teachers anywhere will be able to access these data with obvious benefits for the realization of grander scale collaborative projects. Educational VO data will also be an important resource for teachers not having direct access to any educational telescopes. We will use the educational telescope at our observatory in Trieste as a prototype for the future VO educational data archive resource. The publishing infrastructure will include: user authentication, content and curation validation, data validation and ingestion, VO compliant resource generation. All of these parts will be performed by means of server side applications accessible through a web graphical user interface (web GUI). Apart from user registration, that will be validated by a natural person responsible for the archive (after having verified the reliability of the user and inspected one or more test files), all the subsequent steps will be automated. This means that at the very first data submission through the webGUI, a complete resource including archive and published VO service will be generated, ready to be registered to the VO. The efforts required to the registered user will consist only in describing herself/himself at registration step and submitting the data she/he selects for publishing after each observation sessions. The infrastructure will be file format independent and the underlying data model will use a minimal set of standard VO keywords, some of which will be specific for outreach and education, possibly including VO

  7. Rates of oxygen uptake increase independently of changes in heart rate in late stages of development and at hatching in the green iguana, Iguana iguana.

    Science.gov (United States)

    Sartori, Marina R; Abe, Augusto S; Crossley, Dane A; Taylor, Edwin W

    2017-03-01

    Oxygen consumption (VO 2 ), heart rate (f H ), heart mass (M h ) and body mass (M b ) were measured during embryonic incubation and in hatchlings of green iguana (Iguana iguana). Mean f H and VO 2 were unvarying in early stage embryos. VO 2 increased exponentially during the later stages of embryonic development, doubling by the end of incubation, while f H was constant, resulting in a 2.7-fold increase in oxygen pulse. Compared to late stage embryos, the mean inactive level of VO 2 in hatchlings was 1.7 fold higher, while f H was reduced by half resulting in a further 3.6 fold increase in oxygen pulse. There was an overall negative correlation between mean f H and VO 2 when data from hatchlings was included. Thus, predicting metabolic rate as VO 2 from measurements of f H is not possible in embryonic reptiles. Convective transport of oxygen to supply metabolism during embryonic incubation was more reliably indicated as an index of cardiac output (CO i ) derived from the product of f H and M h . However, a thorough analysis of factors determining rates of oxygen supply during development and eclosion in reptiles will require cannulation of blood vessels that proved impossible in the present study, to determine oxygen carrying capacity by the blood and arteriovenous oxygen content difference (A-V diff), plus patterns of blood flow. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Extending Tactical Fleet Communications Through VoIP

    Science.gov (United States)

    2014-09-01

    corporate world , the military is leveraging VoIP communication solutions as well. Shore commands like Tactical Training Group Pacific use VoIP for...VoIP fuzzing (e.g., Asteroid , PROTOS, Sip-Proxy)  VoIP signaling manipulation (e.g., IAXAuthJack, IAXHangup, SIP-Kill)  VoIP media...as well, but instead of just matching the information to rules, it compares synchronization information between the protocols to determine if the

  9. Oscillation of tissue oxygen index in non-exercising muscle during exercise.

    Science.gov (United States)

    Yano, T; Afroundeh, R; Shirakawa, K; Lian, C-S; Shibata, K; Xiao, Z; Yunoki, T

    2015-09-01

    The purpose of the present study was to examine how oscillation of tissue oxygen index (TOI) in non-exercising exercise is affected during high-intensity and low-intensity exercises. Three exercises were performed with exercise intensities of 30% and 70% peak oxygen uptake (Vo(2)peak) for 12 min and with exercise intensity of 70% Vo(2)peak for 30 s. TOI in non-exercising muscle (biceps brachii) during the exercises for 12 min was determined by nearinfrared spectroscopy. TOI in the non-exercising muscle during the exercises was analyzed by fast Fourier transform (FFT) to obtain power spectra density (PSD). The frequency at which maximal PSD appeared (Fmax) during the exercise with 70% Vo(2)peak for 12 min (0.00477 ± 0.00172 Hz) was significantly lower than that during the exercise with 30% Vo2peak for 12 min (0.00781 ± 0.00338 Hz). There were significant differences in blood pH and blood lactate between the exercise with 70% Vo(2)peak and the exercise with 30% Vo(2)peak. It is concluded that TOI in nonexercising muscle oscillates during low-intensity exercise as well as during high-intensity exercise and that the difference in Fmax between the two exercises is associated with the difference in increase in blood lactate derived from the exercise.

  10. Electron diffraction study of the sillenites Bi{sub 12}SiO{sub 20}, Bi{sub 25}FeO{sub 39} and Bi{sub 25}InO{sub 39}: Evidence of short-range ordering of oxygen-vacancies in the trivalent sillenites

    Energy Technology Data Exchange (ETDEWEB)

    Scurti, Craig A.; Arenas, D. J. [Department of Physics, University of North Florida, Jacksonville, FL 32224 (United States); Auvray, Nicolas [Department of Physics, University of North Florida, Jacksonville, FL 32224 (United States); Laboratoire de Nanotechnologie et d’Instrumentation Optique - UMR CNRS 6279, Université Technologie de Troyes, 12 rue Marie Curie, Troyes 10010 (France); Lufaso, Michael W. [Department of Chemistry, University of North Florida, Jacksonville, FL 32224 (United States); Takeda, Seiji [The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Kohno, Hideo [School of Environmental Science and Engineering, Kochi University of Technology, Tosayamada, Kami, Kochi 782-8502 Japan (Japan)

    2014-08-15

    We present an electron diffraction study of three sillenites, Bi{sub 12}SiO{sub 20}, Bi{sub 25}FeO{sub 39}, and Bi{sub 25}InO{sub 39} synthesized using the solid-state method. We explore a hypothesis, inspired by optical studies in the literature, that suggests that trivalent sillenites have additional disorder not present in the tetravalent compounds. Electron diffraction patterns of Bi{sub 25}FeO{sub 39} and Bi{sub 25}InO{sub 39} show streaks that confirm deviations from the ideal sillenite structure. Multi-slice simulations of electron-diffraction patterns are presented for different perturbations to the sillenite structure - partial substitution of the M site by Bi{sup 3+}, random and ordered oxygen-vacancies, and a frozen-phonon model. Although comparison of experimental data to simulations cannot be conclusive, we consider the streaks as evidence of short-range ordered oxygen-vacancies.

  11. High temperature oxidation of metals: vacancy injection and consequences on the mechanical properties

    International Nuclear Information System (INIS)

    Perusin, S.

    2004-11-01

    The aim of this work is to account for the effects of the high temperature oxidation of metals on their microstructure and their mechanical properties. 'Model' materials like pure nickel, pure iron and the Ni-20Cr alloy are studied. Nickel foils have been oxidised at 1000 C on one side only in laboratory air, the other side being protected from oxidation by a reducing atmosphere. After the oxidation treatment, the unoxidized face was carefully examined by using an Atomic Force Microscope (AFM). Grain boundaries grooves were characterised and their depth were compared to the ones obtained on the same sample heat treated in the reducing atmosphere during the same time. They are found to be much deeper in the case of the single side oxidised samples. It is shown that this additional grooving is directly linked to the growth of the oxide scale on the opposite side and that it can be explained by the diffusion of the vacancies produced at the oxide scale - metal interface, across the entire sample through grain boundaries. Moreover, the comparison between single side oxidised samples and samples oxidised on both sides points out that voids in grain boundaries are only observed in this latter case proving the vacancies condensation in the metal when the two faces are oxidised. The role of the carbon content and the sample's geometry on this phenomenon is examined in detail. The diffusion of vacancies is coupled with the transport of oxygen so that a mechanism of oxygen transport by vacancies is suggested. The tensile tests realised at room temperature on nickel foils (bamboo microstructure) show that the oxide scale can constitute a barrier to the emergence of dislocations at the metal surface. Finally, the Ni-20Cr alloy is tested in tensile and creep tests between 25 and 825 C in oxidising or reducing atmospheres. (author)

  12. Oxygen vacancy defect engineering using atomic layer deposited HfAlOx in multi-layered gate stack

    Science.gov (United States)

    Bhuyian, M. N.; Sengupta, R.; Vurikiti, P.; Misra, D.

    2016-05-01

    This work evaluates the defects in high quality atomic layer deposited (ALD) HfAlOx with extremely low Al (estimated by the high temperature current voltage measurement shows that the charged oxygen vacancies, V+/V2+, are the primary source of defects in these dielectrics. When Al is added in HfO2, the V+ type defects with a defect activation energy of Ea ˜ 0.2 eV modify to V2+ type to Ea ˜ 0.1 eV with reference to the Si conduction band. When devices were stressed in the gate injection mode for 1000 s, more V+ type defects are generated and Ea reverts back to ˜0.2 eV. Since Al has a less number of valence electrons than do Hf, the change in the co-ordination number due to Al incorporation seems to contribute to the defect level modifications. Additionally, the stress induced leakage current behavior observed at 20 °C and at 125 °C demonstrates that the addition of Al in HfO2 contributed to suppressed trap generation process. This further supports the defect engineering model as reduced flat-band voltage shifts were observed at 20 °C and at 125 °C.

  13. Structural analysis of LaVO3 thin films under epitaxial strain

    Directory of Open Access Journals (Sweden)

    H. Meley

    2018-04-01

    Full Text Available Rare earth vanadate perovskites exhibit a phase diagram in which two different types of structural distortions coexist: the strongest, the rotation of the oxygen octahedra, comes from the small tolerance factor of the perovskite cell (t = 0.88 for LaVO3 and the smaller one comes from inter-site d-orbital interactions manifesting as a cooperative Jahn-Teller effect. Epitaxial strain acts on octahedral rotations and crystal field symmetry to alter this complex lattice-orbit coupling. In this study, LaVO3 thin film structures have been investigated by X-ray diffraction and scanning transmission electron microscopy. The analysis shows two different orientations of octahedral tilt patterns, as well as two distinct temperature behaviors, for compressive and tensile film strain states. Ab initio calculations capture the strain effect on the tilt pattern orientation in agreement with experimental data.

  14. Oxygen vacancy as fatigue evidence of La0.5Sr0.5CoO3/PbZr0.4Ti0.6O3/La0.5Sr0.5CoO3 capacitors

    Science.gov (United States)

    Liu, B. T.; Chen, J. E.; Sun, J.; Wei, D. Y.; Chen, J. H.; Li, X. H.; Bian, F.; Zhou, Y.; Guo, J. X.; Zhao, Q. X.; Guan, L.; Wang, Y. L.; Guo, Q. L.; Ma, L. X.

    2010-09-01

    La0.5Sr0.5CoO3 (LSCO) films grown on SrTiO3 substrates, cooled at reduced oxygen pressures, ranging from 8×104 to 1×10-4 Pa, from the depostion temperature, are used as the bottom electrodes of PbZr0.4Ti0.6O3 (PZT) capacitors to study the impact of oxygen stoichiometry of the LSCO bottom electrodes on the structural and physical properties of LSCO/PZT/LSCO capacitors. It is found that the tetragonality, polarization and fatigue-resistance of PZT films decrease with the decrease of the cooling oxygen pressure. Almost 60% polarization degradation occurs for the PZT capacitor with the LSCO bottom electrode cooled in 1×10-4 Pa oxygen up to 1010 switching cycles, indicating that the oxygen vacancy of the bottom electrode can result in fatigue of the LSCO/PZT/LSCO capacitor.

  15. Oxygen pressure manipulations on the metal-insulator transition characteristics of highly (011)-oriented vanadium dioxide films grown by magnetron sputtering

    International Nuclear Information System (INIS)

    Yu Qian; Li Wenwu; Duan Zhihua; Hu Zhigao; Chu Junhao; Liang Jiran; Chen Hongda; Liu Jian

    2013-01-01

    The metal-insulator transition behaviour of vanadium dioxide (VO 2 ) films grown at different oxygen pressures is investigated. With the aid of temperature-dependent electrical and infrared transmittance experiments, it is found that the transition temperature in the heating process goes up with increasing argon-oxygen ratio, whereas the one in the cooling process shows an inverse variation trend. It is found that the hysteresis width of the phase transition is narrowed at a lower argon-oxygen ratio because the defects introduced by excess oxygen lower the energy requirement of transformation. Furthermore, the defects reduce the forbidden gap of the VO 2 system due to the generation of a V 5+ ion. The present results are valuable for the achievement of VO 2 -based optoelectronic devices.

  16. Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process

    Science.gov (United States)

    Zhu, Nai-Wei; Hu, Ming; Xia, Xiao-Xu; Wei, Xiao-Ying; Liang, Ji-Ran

    2014-04-01

    The VO2 thin film with high performance of metal-insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-°C hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively.

  17. Zn-vacancy related defects in ZnO grown by pulsed laser deposition

    Science.gov (United States)

    Ling, F. C. C.; Luo, C. Q.; Wang, Z. L.; Anwand, W.; Wagner, A.

    2017-02-01

    Undoped and Ga-doped ZnO (002) films were grown c-sapphire using the pulsed laser deposition (PLD) method. Znvacancy related defects in the films were studied by different positron annihilation spectroscopy (PAS). These included Doppler broadening spectroscopy (DBS) employing a continuous monenergetic positron beam, and positron lifetime spectroscopy using a pulsed monoenergetic positron beam attached to an electron linear accelerator. Two kinds of Znvacancy related defects namely a monovacancy and a divacancy were identified in the films. In as-grown undoped samples grown with relatively low oxygen pressure P(O2)≤1.3 Pa, monovacancy is the dominant Zn-vacancy related defect. Annealing these samples at 900 oC induced Zn out-diffusion into the substrate and converted the monovacancy to divacancy. For the undoped samples grown with high P(O2)=5 Pa irrespective of the annealing temperature and the as-grown degenerate Ga-doped sample (n=1020 cm-3), divacancy is the dominant Zn-vacancy related defect. The clustering of vacancy will be discussed.

  18. Performance of VoIP on HSDPA

    DEFF Research Database (Denmark)

    Wang, Bang; Pedersen, Klaus I.; Kolding, Troels E.

    2005-01-01

    This paper provides packet scheduler design and performance simulations for running VoIP services over high-speed downlink packet access (HSDPA) in WCDMA. The main challenge of supporting VoIP service on HSDPA is the tight delay requirement combined with the small VoIP packet size. A packet...... scheduler design incorporating VoIP packet aggregation and user multiplexing is proposed and the VoIP capacity is studied for a macro-cellular environment. Results are obtained for different delay budgets and packet scheduling settings, using either blind round robin or a slightly modified version...... of proportional fair scheduling. For proportional fair scheduling with code-multiplexing of 4-users, the downlink VoIP cell capacity on HSDPA is found to be in the range 72-104 users depending on whether the delay budget for the Node-B scheduling and user reception equals 80 ms or 150 ms, respectively....

  19. Submaximal oxygen uptake kinetics, functional mobility, and physical activity in older adults with heart failure and reduced ejection fraction.

    Science.gov (United States)

    Hummel, Scott L; Herald, John; Alpert, Craig; Gretebeck, Kimberlee A; Champoux, Wendy S; Dengel, Donald R; Vaitkevicius, Peter V; Alexander, Neil B

    2016-07-01

    Submaximal oxygen uptake measures are more feasible and may better predict clinical cardiac outcomes than maximal tests in older adults with heart failure (HF). We examined relationships between maximal oxygen uptake, submaximal oxygen kinetics, functional mobility, and physical activity in older adults with HF and reduced ejection fraction. Older adults with HF and reduced ejection fraction (n = 25, age 75 ± 7 years) were compared to 25 healthy age- and gender-matched controls. Assessments included a maximal treadmill test for peak oxygen uptake (VO2peak), oxygen uptake kinetics at onset of and on recovery from a submaximal treadmill test, functional mobility testing [Get Up and Go (GUG), Comfortable Gait Speed (CGS), Unipedal Stance (US)], and self-reported physical activity (PA). Compared to controls, HF had worse performance on GUG, CGS, and US, greater delays in submaximal oxygen uptake kinetics, and lower PA. In controls, VO2peak was more strongly associated with functional mobility and PA than submaximal oxygen uptake kinetics. In HF patients, submaximal oxygen uptake kinetics were similarly associated with GUG and CGS as VO2peak, but weakly associated with PA. Based on their mobility performance, older HF patients with reduced ejection fraction are at risk for adverse functional outcomes. In this population, submaximal oxygen uptake measures may be equivalent to VO2 peak in predicting functional mobility, and in addition to being more feasible, may provide better insight into how aerobic function relates to mobility in older adults with HF.

  20. VoIP over WLAN

    OpenAIRE

    Nikkari, Joni

    2007-01-01

    Tässä opinnäytetyössä tutkitaan VoIP over WLAN -tekniikan mahdollisuuksia nykyaikaisessa käyttöympäristössä, sekä yritysmaailman että kotikäyttäjän näkökulmasta. Toimiakseen VoWLAN tarvitsee kaksi eri tekniikkaa: langattoman lähiverkon sekä WLAN-puhelimen, joka perustuu VoIP-tekniikkaan.; WLAN:ssa tietoliikenne kulkee normaalin kaapeloinnin sijasta radiotaajuuksia käyttämällä. Standardina toimii IEEE 802.11, joka määrittelee WLAN-verkkojen toiminnan. Standardia on kehitetty jatkuvasti, ja si...

  1. Thermal conductivity reduction in oxygen-deficient strontium titanates

    NARCIS (Netherlands)

    Yu, Choongho; Scullin, Matthew L.; Huijben, Mark; Ramesh, Ramamoorthy; Majumdar, Arun

    2008-01-01

    We report significant thermal conductivity reduction in oxygen-deficient lanthanum-doped strontium titanate (Sr1−xLaxTiO3−δ) films as compared to unreduced strontium titanates. Our experimental results suggest that the oxygen vacancies could have played an important role in the reduction. This could

  2. Muscle mitochondrial capacity exceeds maximal oxygen delivery in humans

    DEFF Research Database (Denmark)

    Boushel, Robert Christopher; Gnaiger, Erich; Calbet, Jose A L

    2011-01-01

    Across a wide range of species and body mass a close matching exists between maximal conductive oxygen delivery and mitochondrial respiratory rate. In this study we investigated in humans how closely in-vivo maximal oxygen consumption (VO(2) max) is matched to state 3 muscle mitochondrial respira...

  3. Positron lifetime in vacancy clusters. Application to the study of vacancy-impurity interactions

    International Nuclear Information System (INIS)

    Corbel, C.

    1986-02-01

    Positron lifetime measurements are used to study the vacancy recovery (77-650 K) in 20 K electron irradiated dilute gold or iron alloys in stainless steels. Positron lifetimes in clusters of various shapes and structures are calculated to precise the information obtained by measuring the positron lifetime in a vacancy cluster of unknown size and configuration. From the calculations, we have drawn the following conclusions: - the minimal size of an unknown cluster can be deduced from the measurement of the positron lifetime in the cluster; - a decrease of the positron lifetime when the structure of the cluster evolves, means either a decrease of the size of the cluster, or, the appearance of a relaxed configuration. - The positron lifetime is very useful to discriminate between a spatial planar or relaxed configuration and a tri-dimensional one. In AuGe, AuSb, AuTn alloys, vacancy clusters decorated by solute atoms appear at 250 K. Their configurations are different from those in pure Au. Mobile vacancy-solutes complexes are involved in the clustering process in AuGe, AuSb. The clusters are probably decorated by several solute atoms in AuGe and AuSb where the resistivity evidences a clustering of solute atoms. In AuFe, vacancy-single or multi-complexes stable up to 670 K prevent cluster formation. In FeTi, FeSb, FeAu, vacancy migration is hindered by the formation of vacancy-solute complexes up to 315 K (Ti), up to 670 K (Sb), up to 700 K (Au). In FeSi, FeCu, FeAg, tri-dimensional clusters grow less easily than Fe. This is likely due to the formation of several kinds of small decorated clusters with relaxed or planar configurations. They are peculiarly stable, surviving up to 700 K at least. In Si (resp. Ti) doped 59Fe25Ni16Cr, solute atoms retain the vacancies up to 300 K (resp. 320 K) [fr

  4. Escala de VO2pico em adolescentes obesos e não-Obesos por diferentes métodos Escala de VO2pico en adolescentes obesos y no obesos por diferentes métodos Scale of VO2peak in obese and non-obese adolescents by different methods

    Directory of Open Access Journals (Sweden)

    Gerusa Eisfeld Milano

    2009-12-01

    estrategia atractiva para comparar individuos con grandes diferencias en la masa corporal. OBJETIVO: Investigar el VO2pico en individuos obesos y no obesos usando el método de corrección de masa corporal (convencional y la escala alométrica (método alométrico y cómo esos métodos se aplican cuando individuos de ambos sexos se ejercitan en una cinta ergométrica. MÉTODOS: El VO2pico relativo al peso corporal y por el método alométrico fue comparado en 54 adolescentes obesos y 33 no obesos (10-16 años. Para evaluar el VO2pico durante un test máximo se utilizó calorimetría indirecta. El exponente alométrico fue calculado considerando la masa corporal individual. Así, el VO2pico fue corregido mediante el exponente alométrico. Las comparaciones se realizaron utilizando two-way ANOVA para medidas repetidas (p0,05. Sin embargo, el VO2pico calculado por el método convencional fue mayor (p0.05 entre los grupos. CONCLUSIÓN: Los individuos obesos presentaron VO2pico más bajo que los no obesos, al ser evaluados mediante el método convencional. Sin embargo, las diferencias desaparecieron cuando se aplicó el método de la escala alométrica.BACKGROUND: Peak oxygen uptake (VO2peak can be defined as the highest oxygen rate consumed during exhaustive or maximal exercise. The evaluation of the aerobic fitness can be expressed as relative to body mass, but this procedure may not fully remove differences when heavy subjects are assessed. Thus, the allometric scaling procedure is an attractive strategy to compare individuals with large differences in body mass. OBJECTIVE: Investigate VO2peak in obese and non-obese individuals using body mass correction (conventional and allometric scaling (allometric methods and how these methods apply when subjects of different genders exercise on a treadmill. METHODS: VO2peak relative to body weight and measured by the allometric method were compared in 54 obese and 33 non-obese adolescents (10 a 16 years. Indirect calorimetry was used to

  5. Phosphorous–vacancy–oxygen defects in silicon

    KAUST Repository

    Wang, Hao; Chroneos, Alexander; Hall, D.; Schwingenschlö gl, Udo; Sgourou, E. N.

    2013-01-01

    Electronic structure calculations employing the hybrid functional approach are used to gain fundamental insight in the interaction of phosphorous with oxygen interstitials and vacancies in silicon. It recently has been proposed, based on a binding

  6. A novel inorganic precipitation-peptization method for VO2 sol and VO2 nanoparticles preparation: Synthesis, characterization and mechanism.

    Science.gov (United States)

    Li, Yao; Jiang, Peng; Xiang, Wei; Ran, Fanyong; Cao, Wenbin

    2016-01-15

    In this paper, a simple, safe and cost-saving precipitation-peptization method was proposed to prepare VO2 sol by using inorganic VOSO4-NH3⋅H2O-H2O2 reactants system in air under room temperature. In this process, VOSO4 was firstly precipitated to form VO(OH)2, then monometallic species of VO(O2)(OH)(-) were formed through the coordination between VO(OH)2 and H2O2. The rearrangement of VO(O2)(OH)(-) in a nonplanar pattern and intermolecular condensation reactions result in multinuclear species. Finally, VO2 sol is prepared through the condensation reactions between the multinuclear species. After drying the obtained sol at 40°C, VO2 xerogel exhibiting monoclinic crystal structure with the space group of C2/m was prepared. The crystal structure of VO2 nanoparticles was transferred to monoclinic crystal structure with the space group of P21/c (VO2(M)) by annealing the xerogel at 550°C. Both XRD and TEM analysis indicated that the nanoparticles possess good crystallinity with crystallite size of 34.5nm as estimated by Scherrer's method. These results suggest that the VO2 sol has been prepared successfully through the proposed simple method. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. First-principles study on migration of vacancy in tungsten

    International Nuclear Information System (INIS)

    Oda, Yasuhiro; Ito, Atsushi M.; Takayama, Arimichi; Nakamura, Hiroaki

    2014-03-01

    We calculated di-vacancy binding energies and migration energies of mono-vacancy and di-vacancy in tungsten material using DFT calculation. The mono-vacancy diffuses in [111] direction easily rather than in [001] direction. The migration energies of di-vacancies are almost the same value of the mono-vacancy. The migration of di-vacancy is approximately the same as the migration of mono-vacancy. The di-vacancy binding energies are almost zero or negative. The interactions between two vacancies in tungsten material are repulsive from the second to fifth nearest-neighbor. The vacancies are difficult to aggregate since di-vacancy is less stable than mono-vacancy. (author)

  8. VO-Dance an IVOA tools to easy publish data into VO and it's extension on planetology request

    Science.gov (United States)

    Smareglia, R.; Capria, M. T.; Molinaro, M.

    2012-09-01

    Data publishing through the self standing portals can be joined to VO resource publishing, i.e. astronomical resources deployed through VO compliant services. Since the IVOA (International Virtual Observatory Alliance) provides many protocols and standards for the various data flavors (images, spectra, catalogues … ), and since the data center has as a goal to grow up in number of hosted archives and services providing, the idea arose to find a way to easily deploy and maintain VO resources. VO-Dance is a java web application developed at IA2 that addresses this idea creating, in a dynamical way, VO resources out of database tables or views. It is structured to be potentially DBMS and platform independent and consists of 3 main tokens, an internal DB to store resources description and model metadata information, a restful web application to deploy the resources to the VO community. It's extension to planetology request is under study to best effort INAF software development and archive efficiency.

  9. Indium vacancy induced d0 ferromagnetism in Li-doped In2O3 nanoparticles

    Science.gov (United States)

    Cao, Haiming; Xing, Pengfei; Zhou, Wei; Yao, Dongsheng; Wu, Ping

    2018-04-01

    Li-doped In2O3 nanoparticles with room temperature d0 ferromagnetism were prepared by a sol-gel method. X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence were carried out to investigate the effects of Li incorporation on the lattice defects. As the content of Li increases, non-monotonic changes in shifts of XRD peak (2 2 2) and the intensity ratios of indium vacancies related photoluminescence peak (PII) with respect to oxygen vacancies related peak (PI) are observed. Results show that at low doping level (≤2 at.%) Li prefers to occupy In sites, while with further doping the interstitial sites are more favorable for Li. Combined with the consistent non-monotonic change in saturation magnetization, we think that indium vacancies resulting from Li-doping play an important role in inducing d0 ferromagnetism in our Li-doped In2O3 nanoparticles, and the FM coupling is mainly mediated by the LiIn-ONN-VIn-ONN-LiIn chains.

  10. Physicochemical characterization of point defects in fluorine doped tin oxide films

    Science.gov (United States)

    Akkad, Fikry El; Joseph, Sudeep

    2012-07-01

    The physical and chemical properties of spray deposited FTO films are studied using FESEM, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), electrical and optical measurements. The results of XRD measurements showed that the films are polycrystalline (grain size 20-50 nm) with Rutile structure and mixed preferred orientation along the (200) and (110) planes. An angular shift of the XRD peaks after F-doping is observed and interpreted as being due to the formation of substitutional fluorine defects (FO) in presence of high concentration of oxygen vacancies (VO) that are electrically neutral. The electrical neutrality of oxygen vacancies is supported by the observation that the electron concentration n is two orders of magnitude lower than the VO concentration calculated from chemical analyses using XPS measurements. It is shown that an agreement between XPS, XRD, and Hall effect results is possible provided that the degree of deviation from stoichiometry is calculated with the assumption that the major part of the bulk carbon content is involved in O-C bonds. High temperature thermal annealing is found to cause an increase in the FO concentration and a decrease in both n and VO concentrations with the increase of the annealing temperature. These results could be interpreted in terms of a high temperature chemical exchange reaction between the SnO2 matrix and a precipitated fluoride phase. In this reaction, fluorine is released to the matrix and Sn is trapped by the fluoride phase, thus creating substitutional fluorine FO and tin vacancy VSn defects. The enthalpy of this reaction is determined to be approximately 2.4 eV while the energy of formation of a VSn through the migration of SnSn host atom to the fluoride phase is approximately 0.45 eV.

  11. Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3

    Science.gov (United States)

    Mattoni, Giordano; Filippetti, Alessio; Manca, Nicola; Zubko, Pavlo; Caviglia, Andrea D.

    2018-05-01

    Tungsten trioxide (WO3) is a versatile material with widespread applications ranging from electrochromics and optoelectronics to water splitting and catalysis of chemical reactions. For technological applications, thin films of WO3 are particularly appealing, taking advantage from a high surface-to-volume ratio and tunable physical properties. However, the growth of stoichiometric crystalline thin films is challenging because the deposition conditions are very sensitive to the formation of oxygen vacancies. In this paper, we show how background oxygen pressure during pulsed laser deposition can be used to tune the structural and electronic properties of WO3 thin films. By performing x-ray diffraction and low-temperature electrical transport measurements, we find changes in the WO3 lattice volume of up to 10% concomitantly with a resistivity drop of more than five orders of magnitude at room temperature as a function of increased oxygen deficiency. We use advanced ab initio calculations to describe in detail the properties of the oxygen vacancy defect states and their evolution in terms of excess charge concentration. Our results depict an intriguing scenario where structural, electronic, optical, and transport properties of WO3 single-crystal thin films can all be purposely tuned by controlling the oxygen vacancy formation during growth.

  12. Theoretical study of the influence of cation vacancies on the catalytic properties of vanadium antimonate

    International Nuclear Information System (INIS)

    Messina, S.; Juan, A.; Larrondo, S.; Irigoyen, B.; Amadeo, N.

    2008-01-01

    We have theoretically studied the influence of antimony and vanadium cation vacancies in the electronic structure and reactivity of vanadium antimonate, using molecular orbital methods. From the analysis of the electronic properties of the VSbO 4 crystal structure, we can infer that both antimony and vanadium vacancies increase the oxidation state of closer V cations. This would indicate that, in the rutile-type VSbO 4 phase the Sb and V cations defects stabilize the V in a higher oxidation state (V 4+ ). Calculations of the adsorption energy for different toluene adsorption geometries on the VSbO 4 (1 1 0) surface have also been performed. The oxidation state of Sb, V and O atoms and the overlap population of metal-oxygen bonds have been evaluated. Our results indicate that the cation defects influence in the toluene adsorption reactions is slight. We have computed different alternatives for the reoxidation of the VSbO 4 (1 1 0) surface active sites which were reduced during the oxygenated products formation. These calculations indicate that the V cations in higher oxidation state (V 4+ ) are the species, which preferentially incorporate lattice oxygen to the reduced Sb cations. Thus, the cation defects would stabilize the V 4+ species in the VSbO 4 structure, determining its ability to provide lattice oxygen as a reactant

  13. Solute-vacancy binding in aluminum

    International Nuclear Information System (INIS)

    Wolverton, C.

    2007-01-01

    Previous efforts to understand solute-vacancy binding in aluminum alloys have been hampered by a scarcity of reliable, quantitative experimental measurements. Here, we report a large database of solute-vacancy binding energies determined from first-principles density functional calculations. The calculated binding energies agree well with accurate measurements where available, and provide an accurate predictor of solute-vacancy binding in other systems. We find: (i) some common solutes in commercial Al alloys (e.g., Cu and Mg) possess either very weak (Cu), or even repulsive (Mg), binding energies. Hence, we assert that some previously reported large binding energies for these solutes are erroneous. (ii) Large binding energies are found for Sn, Cd and In, confirming the proposed mechanism for the reduced natural aging in Al-Cu alloys containing microalloying additions of these solutes. (iii) In addition, we predict that similar reduction in natural aging should occur with additions of Si, Ge and Au. (iv) Even larger binding energies are found for other solutes (e.g., Pb, Bi, Sr, Ba), but these solutes possess essentially no solubility in Al. (v) We have explored the physical effects controlling solute-vacancy binding in Al. We find that there is a strong correlation between binding energy and solute size, with larger solute atoms possessing a stronger binding with vacancies. (vi) Most transition-metal 3d solutes do not bind strongly with vacancies, and some are even energetically strongly repelled from vacancies, particularly for the early 3d solutes, Ti and V

  14. Magnetism and metal-insulator transition in oxygen deficient SrTiO3

    Science.gov (United States)

    Lopez-Bezanilla, Alejandro; Ganesh, P.; Littlewood, Peter

    2015-03-01

    We report new findings in the electronic structure and magnetism of oxygen vacancies in SrTiO3. By means of first-principles calculations we show that the appearance of magnetism in oxygen-deficient SrTiO3 is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. While an isolated vacancy behaves as a non-magnetic double donor, manipulation of the doping conditions allows the stability of a single donor state with emergent local moments. Strong local lattice distortions enhance the binding of this state. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient SrTiO3, which may have important implications in the design of switchable magneto-optic devices. AL-B and PBL were supported by DOE-BES under Contract No. DE-AC02-06CH11357. PG was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT- Battelle, LLC, for the US Department of Energy.

  15. THE CONTRIBUTION OF 'RESTING' BODY MUSCLES TO THE SLOW COMPONENT OF PULMONARY OXYGEN UPTAKE DURING HIGH-INTENSITY CYCLING

    Directory of Open Access Journals (Sweden)

    Susan A. Ward

    2012-12-01

    Full Text Available Oxygen uptake (VO2 kinetics during moderate constant- workrate (WR exercise (>lactate-threshold (ӨL are well described as exponential. AboveӨL, these kinetics are more complex, consequent to the development of a delayed slow component (VO2sc, whose aetiology remains controversial. To assess the extent of the contribution to the VO2sc from arm muscles involved in postural stability during cycling, six healthy subjects completed an incremental cycle-ergometer test to the tolerable limit for estimation of ӨL and determination of peak VO2. They then completed two constant-WR tests at 90% of ӨL and two at 80% of ∆ (difference between ӨL and VO2peak. Gas exchange variables were derived breath-by-breath. Local oxygenation profiles of the vastus lateralis and biceps brachii muscles were assessed by near-infrared spectroscopy, with maximal voluntary contractions (MVC of the relevant muscles being performed post-exercise to provide a frame of reference for normalising the exercise-related oxygenation responses across subjects. Above supra-ӨL, VO2 rose in an exponential-like fashion ("phase 2, with a delayed VO2sc subsequently developing. This was accompanied by an increase in [reduced haemoglobin] relative to baseline (∆[Hb], which attained 79 ± 13 % (mean, SD of MVC maximum in vastus lateralis at end-exercise and 52 ± 27 % in biceps brachii. Biceps brachii ∆[Hb] was significantly correlated with VO2 throughout the slow phase. In contrast, for sub- L exercise, VO2 rose exponentially to reach a steady state with a more modest increase in vastus lateralis ∆[Hb] (30 ± 11 %; biceps brachii ∆[Hb] was minimally affected (8 ± 2 %. That the intramuscular O2 desaturation profile in biceps brachii was proportional to that for VO2sc during supra-ӨL cycle ergometry is consistent with additional stabilizing arm work contributing to the VO2sc

  16. Ab initio study of vacancy formation in cubic LaMnO{sub 3} and SmCoO{sub 3} as cathode materials in solid oxide fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Olsson, Emilia; Aparicio-Anglès, Xavier [Department of Chemistry, University College London, London WC1H 0AJ (United Kingdom); Leeuw, Nora H. de, E-mail: deleeuwn@cardiff.ac.uk [Department of Chemistry, University College London, London WC1H 0AJ (United Kingdom); School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT (United Kingdom)

    2016-07-07

    Doped LaMnO{sub 3} and SmCoO{sub 3} are important solid oxide fuel cell cathode materials. The main difference between these two perovskites is that SmCoO{sub 3} has proven to be a more efficient cathode material than LaMnO{sub 3} at lower temperatures. In order to explain the difference in efficiency, we need to gain insight into the materials’ properties at the atomic level. However, while LaMnO{sub 3} has been widely studied, ab initio studies on SmCoO{sub 3} are rare. Hence, in this paper, we perform a comparative DFT + U study of the structural, electronic, and magnetic properties of these two perovskites. To that end, we first determined a suitable Hubbard parameter for the Co d–electrons to obtain a proper description of SmCoO{sub 3} that fully agrees with the available experimental data. We next evaluated the impact of oxygen and cation vacancies on the geometry, electronic, and magnetic properties. Oxygen vacancies strongly alter the electronic and magnetic structures of SmCoO{sub 3}, but barely affect LaMnO{sub 3}. However, due to their high formation energy, their concentrations in the material are very low and need to be induced by doping. Studying the cation vacancy concentration showed that the formation of cation vacancies is less energetically favorable than oxygen vacancies and would thus not markedly influence the performance of the cathode.

  17. Experimental evidence of hydrogen–oxygen decoupled diffusion into BaZr0.6Ce0.25Y0.15O3−δ

    International Nuclear Information System (INIS)

    Lim, D.-K.; Im, H.-N.; Jeon, S.-Y.; Park, J.-Y.; Song, S.-J.

    2013-01-01

    The electrical properties of BaZr 0.6 Ce 0.25 Y 0.15 O 3−δ (BZCY) were studied as a function of both oxygen partial pressure (-2.65⩽log(P O 2 atm -1 )⩽-0.62) and water vapor activity (-3.33⩽log(P H 2 O atm -1 ⩽-1.3)) in the temperature range of 973–1073 K. The total conductivity slightly increased in reducing atmospheres with increasing water vapor activity because of the relative contribution to the total conductivity by the redox reaction at the given thermodynamic conditions. The partial conductivities of protons, holes and oxygen vacancies were successfully calculated, and the activation energy determined for proton transport was 0.3 ± 0.1 eV. The chemical diffusivity of oxygen at a fixed water vapor activity, D ∼ vO , could only be evaluated from Fick’s second law during oxidation and reduction at the fixed water vapor activity. However, twofold nonmonotonic conductivity relaxation behaviors were clearly confirmed in the temperature range investigated during hydration/dehydration. If P O 2 represents the fixed oxygen partial pressure, D ∼ iH is the hydrogen chemical diffusivity at P O 2 and D ∼ vH is the oxygen chemical diffusivity at P O 2 , it was observed that D ∼ iH >D ∼ vH at all experimental conditions, suggesting that the hydrogen chemical diffusion is always faster than oxygen on hydration/dehydration in the temperature range studied

  18. Hydrogen isotope in erbium oxide: Adsorption, penetration, diffusion, and vacancy trapping

    International Nuclear Information System (INIS)

    Mao, Wei; Chikada, Takumi; Suzuki, Akihiro; Terai, Takayuki; Matsuzaki, Hiroyuki

    2015-01-01

    Highlights: • H adsorption on cubic Er 2 O 3 surface results in electron transfer from H to the surface. • The H penetration energy of at least 1.6 eV is required for cubic Er 2 O 3 surface. • The dominated mechanisms of H diffusion in bulk Er 2 O 3 are elucidated. • H diffusion near or at vacancies in Er 2 O 3 is an exothermic reaction. - Abstract: In this study, we report results using first-principles density functional theory calculations for four critical aspects of the interaction: H adsorption on Er 2 O 3 surface, surface-to-subsurface penetration of H into Er 2 O 3 , bulk diffusion of H in Er 2 O 3 , and trapping of H at vacancies. We identify surface stable adsorption positions and find that H prefers to transfer electrons to the surfaces and form covalent bonds with the nearest neighboring four oxygen atoms. For low surface coverage of H as in our case (0.89 × 10 14 H/cm 2 ), a penetration energy of at least 1.60 eV is required for cubic Er 2 O 3 surfaces. Further, the H diffusion barrier between the planes defined by Er 2 O 3 units along the favorable <1 1 1> direction is found to be very small – 0.16 eV – whereas higher barriers of 0.41 eV and 1.64 eV are required for diffusion across the planes, somewhat higher than the diffusion energy barrier of 0.20 eV observed experimentally at 873 K. In addition, we predict that interstitial H is exothermically trapped when it approaches a vacancy with the vacancy defect behaving as an electron trap since the H-vacancy defect is found to be more stable than the intrinsic defect

  19. Mathematical modeling of oxygen transport in solid oxide fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Svensson, Ann Mari

    1997-12-31

    This thesis develops mathematical models to describe the electrochemical performance of a solid oxide fuel cell cathode based on electrochemical kinetics and mass transfer. The individual effects of various coupled processes are investigated. A one-dimensional model is developed based on porous electrode theory. Two different mechanisms are investigated for the charge transfer reaction. One of these assumes that intermediately adsorbed oxygen atoms are reduced at the electrode/electrolyte interface, similar to the models proposed for metal electrodes. Simulated polarization curves exhibit limited currents due to depletion of oxygen adsorbates at high cathodic overvoltages. An empirical correlation is confirmed to exist between the limiting current an the oxygen partial pressure, however, a similar correlation often assumed to exist between the measured polarization resistance and the oxygen partial pressure could not be justified. For the other model, oxygen vacancies are assumed to be exchanged directly at the electrode/electrolyte interface. The electrochemical behaviour is improved by reducing the oxygen partial pressure, due to increased vacancy concentration of the electrode material. Simulated polarization curves exhibit Tafel-like slopes in the cathodic direction, which are due to polarization concentration, and not activation polarization in the conventional sense. Anodic limiting currents are predicted due to lack of available free sites for vacancy exchange at the cathode side. The thesis also presents a theoretical treatment of current and potential distributions in simple two-dimensional cell geometries, and a two-dimensional model for a porous electrode-electrolyte system for investigation of the effect of interfacial diffusion of adsorbates along the electrode/electrolyte interface. 172 refs., 60 figs., 11 tabs.

  20. Machine learning and statistical methods for the prediction of maximal oxygen uptake: recent advances

    Directory of Open Access Journals (Sweden)

    Abut F

    2015-08-01

    Full Text Available Fatih Abut, Mehmet Fatih AkayDepartment of Computer Engineering, Çukurova University, Adana, TurkeyAbstract: Maximal oxygen uptake (VO2max indicates how many milliliters of oxygen the body can consume in a state of intense exercise per minute. VO2max plays an important role in both sport and medical sciences for different purposes, such as indicating the endurance capacity of athletes or serving as a metric in estimating the disease risk of a person. In general, the direct measurement of VO2max provides the most accurate assessment of aerobic power. However, despite a high level of accuracy, practical limitations associated with the direct measurement of VO2max, such as the requirement of expensive and sophisticated laboratory equipment or trained staff, have led to the development of various regression models for predicting VO2max. Consequently, a lot of studies have been conducted in the last years to predict VO2max of various target audiences, ranging from soccer athletes, nonexpert swimmers, cross-country skiers to healthy-fit adults, teenagers, and children. Numerous prediction models have been developed using different sets of predictor variables and a variety of machine learning and statistical methods, including support vector machine, multilayer perceptron, general regression neural network, and multiple linear regression. The purpose of this study is to give a detailed overview about the data-driven modeling studies for the prediction of VO2max conducted in recent years and to compare the performance of various VO2max prediction models reported in related literature in terms of two well-known metrics, namely, multiple correlation coefficient (R and standard error of estimate. The survey results reveal that with respect to regression methods used to develop prediction models, support vector machine, in general, shows better performance than other methods, whereas multiple linear regression exhibits the worst performance

  1. Running Performance, VO2max, and Running Economy: The Widespread Issue of Endogenous Selection Bias.

    Science.gov (United States)

    Borgen, Nicolai T

    2018-05-01

    Studies in sport and exercise medicine routinely use samples of highly trained individuals in order to understand what characterizes elite endurance performance, such as running economy and maximal oxygen uptake VO 2max . However, it is not well understood in the literature that using such samples most certainly leads to biased findings and accordingly potentially erroneous conclusions because of endogenous selection bias. In this paper, I review the current literature on running economy and VO 2max , and discuss the literature in light of endogenous selection bias. I demonstrate that the results in a large part of the literature may be misleading, and provide some practical suggestions as to how future studies may alleviate endogenous selection bias.

  2. Mechanisms of Attenuation of Pulmonary V'O2 Slow Component in Humans after Prolonged Endurance Training.

    Directory of Open Access Journals (Sweden)

    Jerzy A Zoladz

    Full Text Available In this study we have examined the effect of prolonged endurance training program on the pulmonary oxygen uptake (V'O2 kinetics during heavy-intensity cycling-exercise and its impact on maximal cycling and running performance. Twelve healthy, physically active men (mean±SD: age 22.33±1.44 years, V'O2peak 3198±458 mL ∙ min-1 performed an endurance training composed mainly of moderate-intensity cycling, lasting 20 weeks. Training resulted in a decrease (by ~5%, P = 0.027 in V'O2 during prior low-intensity exercise (20 W and in shortening of τp of the V'O2 on-kinetics (30.1±5.9 s vs. 25.4±1.5 s, P = 0.007 during subsequent heavy-intensity cycling. This was accompanied by a decrease of the slow component of V'O2 on-kinetics by 49% (P = 0.001 and a decrease in the end-exercise V'O2 by ~5% (P = 0.005. An increase (P = 0.02 in the vascular endothelial growth factor receptor 2 mRNA level and a tendency (P = 0.06 to higher capillary-to-fiber ratio in the vastus lateralis muscle were found after training (n = 11. No significant effect of training on the V'O2peak was found (P = 0.12. However, the power output reached at the lactate threshold increased by 19% (P = 0.01. The power output obtained at the V'O2peak increased by 14% (P = 0.003 and the time of 1,500-m performance decreased by 5% (P = 0.001. Computer modeling of the skeletal muscle bioenergetic system suggests that the training-induced decrease in the slow component of V'O2 on-kinetics found in the present study is mainly caused by two factors: an intensification of the each-step activation (ESA of oxidative phosphorylation (OXPHOS complexes after training and decrease in the ''additional" ATP usage rising gradually during heavy-intensity exercise.

  3. Mechanisms of Attenuation of Pulmonary V'O2 Slow Component in Humans after Prolonged Endurance Training.

    Science.gov (United States)

    Zoladz, Jerzy A; Majerczak, Joanna; Grassi, Bruno; Szkutnik, Zbigniew; Korostyński, Michał; Gołda, Sławomir; Grandys, Marcin; Jarmuszkiewicz, Wiesława; Kilarski, Wincenty; Karasinski, Janusz; Korzeniewski, Bernard

    2016-01-01

    In this study we have examined the effect of prolonged endurance training program on the pulmonary oxygen uptake (V'O2) kinetics during heavy-intensity cycling-exercise and its impact on maximal cycling and running performance. Twelve healthy, physically active men (mean±SD: age 22.33±1.44 years, V'O2peak 3198±458 mL ∙ min-1) performed an endurance training composed mainly of moderate-intensity cycling, lasting 20 weeks. Training resulted in a decrease (by ~5%, P = 0.027) in V'O2 during prior low-intensity exercise (20 W) and in shortening of τp of the V'O2 on-kinetics (30.1±5.9 s vs. 25.4±1.5 s, P = 0.007) during subsequent heavy-intensity cycling. This was accompanied by a decrease of the slow component of V'O2 on-kinetics by 49% (P = 0.001) and a decrease in the end-exercise V'O2 by ~5% (P = 0.005). An increase (P = 0.02) in the vascular endothelial growth factor receptor 2 mRNA level and a tendency (P = 0.06) to higher capillary-to-fiber ratio in the vastus lateralis muscle were found after training (n = 11). No significant effect of training on the V'O2peak was found (P = 0.12). However, the power output reached at the lactate threshold increased by 19% (P = 0.01). The power output obtained at the V'O2peak increased by 14% (P = 0.003) and the time of 1,500-m performance decreased by 5% (P = 0.001). Computer modeling of the skeletal muscle bioenergetic system suggests that the training-induced decrease in the slow component of V'O2 on-kinetics found in the present study is mainly caused by two factors: an intensification of the each-step activation (ESA) of oxidative phosphorylation (OXPHOS) complexes after training and decrease in the ''additional" ATP usage rising gradually during heavy-intensity exercise.

  4. Positron-annihilation study of oxygen-deficient YBa2Cu3Ox (6.3

    International Nuclear Information System (INIS)

    Tang, C.Q.; Li, B.R.; Chen, A.

    1990-01-01

    We have measured the positron-lifetime spectra of oxygen-deficient YBa 2 Cu 3 O x for 6.3 m , τ 1 , τ 2 , and I 2 have a significant oxygen-content dependence. It is suggested that there are many kinds of positron states in polycrystalline YBa 2 Cu 3 O x , the disordering of O(1) vacancies strongly affects positron lifetime, and with gradually decreasing x the average electronic density decreases and the configuration and/or the charge states of the oxygen vacancies change in the region containing Cu(1)-O(1) chains

  5. Comparative optical study of thulium-doped YVO4 , GdVO4 , and LuVO4 single crystals

    Science.gov (United States)

    Lisiecki, R.; Solarz, P.; Dominiak-Dzik, G.; Ryba-Romanowski, W.; Sobczyk, M.; Černý, Pavel; Šulc, Jan; Jelínková, Helena; Urata, Yoshiharu; Higuchi, Mikio

    2006-07-01

    YVO4:Tm3+ crystals grown by the Czochralski technique and GdVO4:Tm3+ and LuVO4:Tm3+ crystals grown by the floating-zone technique were investigated using methods of optical spectroscopy. Polarized absorption and emission spectra were recorded at room temperature and at 6K . The crystal-field analysis was performed assuming the D2d site symmetry for Tm3+ ions. In this way the missing crystal-field components of the H63 ground multiplet were located. Room temperature absorption spectra were analyzed in the framework of the Judd-Ofelt theory. Evaluated radiative lifetimes of luminescent levels of Tm3+ follow a general trend diminishing in agreement with the sequence: YVO4:Tm3+→GdVO4:Tm3+→LuVO4:Tm3+ . Luminescence lifetimes measured for the systems under study are similar except for the F43 lifetime, which appears to be surprisingly short for LuVO4:Tm3+ . Anisotropy of optical spectra is particularly pronounced in LuVO4:Tm3+ . Peak absorption cross section for the band relevant for optical pumping at about 805nm is roughly three times higher for π polarization. Stimulated emission cross sections for the F43-H63 transition near 1800nm were evaluated using the reciprocity method. The diode-pumped continuous wave laser operation in GdVO4:Tm3+ with a slope efficiency of up to 40% is demonstrated. In LuVO4:Tm3+ the diode-pumped laser oscillation in a pulsed mode was observed.

  6. Response profiles of oxygen uptake efficiency during exercise in healthy children

    NARCIS (Netherlands)

    Bongers, Bart C.; Hulzebos, Erik H J; Helbing, Willem A.; Ten Harkel, Arend D J; Van Brussel, Marco; Takken, Tim

    2015-01-01

    Background Oxygen uptake efficiency (OUE), the relation between oxygen uptake (VO2) and minute ventilation (VE), differs between healthy children and children with heart disease. This study aimed to investigate the normal response profiles of OUE during a progressive cardiopulmonary exercise test.

  7. Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process

    International Nuclear Information System (INIS)

    Zhu Nai-Wei; Hu Ming; Xia Xiao-Xu; Wei Xiao-Ying; Liang Ji-Ran

    2014-01-01

    The VO 2 thin film with high performance of metal–insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO 2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO 2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO 2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-°C hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively. (interdisciplinary physics and related areas of science and technology)

  8. Accessing the VO with Python

    Science.gov (United States)

    Plante, R.; Fitzpatrick, M.; Graham, M.; Tody, D.; Young, W.

    2014-05-01

    We introduce two products for accessing the VO from Python: PyVO and VOClient. PyVO is built on the widely-used Astropy package and is well suited for integrating automated access to astronomical data into highly customizable scripts and applications for data analysis in Python. VOClient is built on a collection of C-libraries and is well suited for integrating with multi-language analysis packages. It also provides a framework for integrating legacy software into the Python environment. In this demo, we will run through several examples demonstrate basic data discovery and retrieval of data. This includes finding archives containing data of interest (VO registry), retrieving datasets (SIA, SSA), and exploring (Cone Search, SLAP). VOClient features some extended capabilities including the ability to communicate to other desktop applications from a script using the SAMP protocol.

  9. Oxygen Transport Membranes

    Energy Technology Data Exchange (ETDEWEB)

    S. Bandopadhyay

    2008-08-30

    The focus of this research was to develop new membrane materials by synthesizing different compounds and determining their defect structures, crystallographic structures and electrical properties. In addition to measuring electrical conductivity, oxygen vacancy concentration was also evaluated using thermogravimetry, Neutron diffraction and Moessbauer Spectroscopy. The reducing conditions (CO{sub 2}/CO/H{sub 2} gas mixtures with steam) as encountered in a reactor environment can be expected to have significant influence on the mechanical properties of the oxides membranes. Various La based materials with and without Ti were selected as candidate membrane materials for OTM. The maximum electrical conductivity of LSF in air as a function of temperature was achieved at < 600 C and depends on the concentration of Sr (acceptor dopant). Oxygen occupancy in LSF was estimated using Neutron diffractometry and Moessbauer Spectroscopy by measuring magnetic moment changes depending on the Fe{sup 3+} and Fe{sup 4+} ratio. After extensive studies of candidate materials, lanthanum ferrites (LSF and LSFT) were selected as the favored materials for the oxygen transport membrane (OTM). LSF is a very good material for an OTM because of its high electronic and oxygen ionic conductivity if long term stability and mechanical strength are improved. LSFT not only exhibits p-type behavior in the high oxygen activity regime, but also has n-type conduction in reducing atmospheres. Higher concentrations of oxygen vacancies in the low oxygen activity regime may improve the performance of LSFT as an OTM. The hole concentration is related to the difference in the acceptor and donor concentration by the relation p = [Sr'{sub La}]-[Ti{sm_bullet}{sub Fe}]. The chemical formulation predicts that the hole concentration is, p = 0.8-0.45 or 0.35. Experimental measurements indicated that p is about {approx} 0.35. The activation energy of conduction is 0.2 eV which implies that LSCF conducts via the

  10. Demokratski stil vođenja

    OpenAIRE

    Roko, Maruna

    2018-01-01

    Djelatnici u poduzeću s demokratskim stilom vođenja moraju biti zadovoljni plaćom i ostalim beneficijama, kao i uvjetima rada, te moraju biti motivirani zahvaljujući nemonotonosti posla i upravljačkim vještinama uprave. Velike prednosti demokratskog stila vođenja su veća fleksibilnost i zarada i izostanak neizvjesnosti i svakodnevnog stresa zbog rizika, dok se teški rad i upornost nagrađuju. Demokratski vođa mora konstantno ispitivati informacije na tržištu prodaje i nabave, proučavati zakons...

  11. Enhanced tunability of electrical and magnetic properties in (La,Sr)MnO3 thin films via field-assisted oxygen vacancy modulation

    Science.gov (United States)

    Wong, Hon Fai; Ng, Sheung Mei; Cheng, Wang Fai; Liu, Yukuai; Chen, Xinxin; von Nordheim, Danny; Mak, Chee Leung; Dai, Jiyan; Ploss, Bernd; Leung, Chi Wah

    2017-12-01

    We investigated the tunability of the transport and magnetic properties in 7.5 nm La0.7Sr0.3MnO3 (LSMO) epitaxial films in a field effect geometry with the ferroelectric copolymer P(VDF-TrFE) as the gate insulator. Two different switching behaviors were observed upon application of gate voltages with either high or low magnitudes. The application of single voltage pulses of alternating polarity with an amplitude high enough to switch the remanent polarization of the ferroelectric copolymer led to a 15% change of the resistance of the LSMO channel at temperature 300 K (but less than 1% change at 20 K). A minimal shift of the peak in the resistance-temperature plot was observed, implying that the Curie temperature TC of the manganite layer is not changed. Alternatively, the application of a chain of low voltage pulses was found to shift TC by more than 16 K, and a change of the channel resistance by a 45% was obtained. We attribute this effect to the field-assisted injection and removal of oxygen vacancies in the LSMO layer, which can occur across the thickness of the oxide film. By controlling the oxygen migration, the low-field switching route offers a simple method for modulating the electric and magnetic properties of manganite films.

  12. Observation of reduced phase transition temperature in N-doped thermochromic film of monoclinic VO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Meinan; Xiong, Mo [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Li, Neng, E-mail: lineng@whut.edu.cn [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Liu, Baoshun; Wang, Shuo [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Ching, Wai-Yim [Department of Physics and Astronomy, University of Missouri-Kansas City, Kansas City, MO 64110 (United States); Zhao, Xiujian, E-mail: opluse@whut.edu.cn [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China)

    2017-07-15

    Highlights: • N-doped VO{sub 2}(M1) thin films have been synthesized by annealing in NH{sub 3} atmosphere. • The phase purity, microstructure and optical property of VO{sub 2} thin film can be regulated by NH{sub 3} concentration. • First-principles calculations have been carried out to study the mechanism of N-doping on energy band structures of VO{sub 2}(M1). • The energy band gaps of VO{sub 2}(M1) are tuned by substitution N-doping or interstitial N-doping. - Abstract: Research on monoclinic (M1) phase of VO{sub 2} has attracted a great of interest for smart coating applications due to its exceptional thermochromic property. Herein, we report the results using a novel approach to synthesize N-doped VO{sub 2}(M1) thin films with high purity by heat treatment in NH{sub 3} atmosphere. The N dopant in the film can be regulated by varying NH{sub 3} concentration during the annealing process. We find that the N atoms are located at the interstitial sites or substitute oxygen atoms, and the V-N bonds in the VO{sub 2} thin films increase with NH{sub 3} concentration. The metal to insulator transition (MIT) temperature (τ{sub c,h}) of the VO{sub 2} thin film is effectively reduced from 80.0 to 62.9 °C, while the solar modulation efficiency (ΔT{sub sol}) and the modulation efficiency at 2000 nm (ΔT{sub 2000nm}) are 7.36% and 55.6% respectively. The band gap of N-doped VO{sub 2} thin films related to MIT (E{sub g1}) is estimated to be as low as 0.18–0.25 eV whereas the band gap associated with the visible transparency (E{sub g2}) is about 1.50–1.58 eV. Based on the highly accurate first-principles calculations, the E{sub g1} of VO{sub 2} (M1) is reduced after substituted or interstitial N-doping, while the E{sub g2} alters with the mode of N-doping, which is excellent agreement with experimental measurement.

  13. Density functional study on the heterogeneous oxidation of NO over α-Fe{sub 2}O{sub 3} catalyst by H{sub 2}O{sub 2}: Effect of oxygen vacancy

    Energy Technology Data Exchange (ETDEWEB)

    Song, Zijian, E-mail: szj22zc15@163.com [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Wang, Ben, E-mail: benwang@hust.edu.cn [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Yu, Jie, E-mail: yujie@hust.edu.cn [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Ma, Chuan, E-mail: machuan628@163.com [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Zhou, Changsong, E-mail: zhouchangsong@hust.edu.cn [School of Energy and Mechanical Engineering, Nanjing Normal University, 210042, Nanjing (China); Chen, Tao, E-mail: chentao_hust@foxmail.com [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Yan, Qianqian [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Wang, Ke, E-mail: m201570959@hust.edu.cn [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China); Sun, Lushi, E-mail: sunlushi@hust.edu.cn [State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 430074, Wuhan (China)

    2017-08-15

    Highlights: • NO and H{sub 2}O{sub 2} adsorption on perfect and oxygen defect α-Fe{sub 2}O{sub 3} (0 0 1) surface were studied by DFT calculations. • H{sub 2}O{sub 2} shows high chemical reactivity for its adsorption on oxygen defect α-Fe{sub 2}O{sub 3} (0 0 1) surface. • Oxygen vacancy plays an important role of the catalytic oxidation of NO by H{sub 2}O{sub 2} over the α-Fe{sub 2}O{sub 3} catalyst surfaces. • Mechanism of NO oxidation over α-Fe{sub 2}O{sub 3} (0 0 1) surface by H{sub 2}O{sub 2} was explained. - Abstract: Catalytic oxidation with H{sub 2}O{sub 2} is a promising method for NOx emission control in coal-fired power plants. Hematite-based catalysts are attracting increased attention because of their surface redox reactivity. To elucidate the NO oxidation mechanism on α-Fe{sub 2}O{sub 3} surfaces, density functional theory (DFT) calculations were conducted by investigating the adsorption characteristics of nitric oxide (NO) and hydrogen peroxide (H{sub 2}O{sub 2}) on perfect and oxygen defect α-Fe{sub 2}O{sub 3} (0 0 1) surfaces. Results show that NO was molecularly adsorbed on two kinds of surfaces. H{sub 2}O{sub 2} adsorption on perfect surface was also in a molecular form; however, H{sub 2}O{sub 2} dissociation occurred on oxygen defect α-Fe{sub 2}O{sub 3} (0 0 1) surface. The adsorption intensities of the two gas molecules in perfect α-Fe{sub 2}O{sub 3} (0 0 1) surface followed the order NO > H{sub 2}O{sub 2}, and the opposite was true for the oxygen defect α-Fe{sub 2}O{sub 3} (0 0 1). Oxygen vacancy remarkably enhanced the adsorption intensities of NO and H{sub 2}O{sub 2} and promoted H{sub 2}O{sub 2} decomposition on catalyst surface. As an oxidative product of NO, HNO{sub 2} was synthesized when NO and H{sub 2}O{sub 2} co-adsorbed on the oxygen defect α-Fe{sub 2}O{sub 3} (0 0 1) surface. Analyses of Mulliken population, electron density difference, and partial density of states showed that H{sub 2}O{sub 2} decomposition

  14. Luminescence Properties of Self-Activated Mm(VO4)2 (M = Mg, Ca, Sr, and Ba) Phosphors Synthesized by Solid-State Reaction Method.

    Science.gov (United States)

    Min, Xin; Huang, Zhaohui; Fang, Minghao; Liu, Yan'gai; Tang, Chao; Wu, Xiaowen

    2016-04-01

    In this paper, M3(VO4)2 (M = Mg, Ca, Sr, and Ba) self-activated phosphors were prepared by a solid-state reaction method at 1,000 °C for 5 h. The phase formation and micrographs were analyzed by X-ray diffraction and scanning electron microscopy. The Ca3(VO4)2 phosphor does not show any emission peaks under excitation with ultraviolet (UV) light. However, the M3(VO4)2 (M = Mg, Sr, and Ba) samples are effectively excited by UV light chips ranging from 200 nm to 400 nm and exhibit broad emission bands due to the charge transfer from the oxygen 2p orbital to the vacant 3d orbital of the vanadium in the VO4. The color of these phosphors changes from yellow to light blue via blue-green with increasing ionic radius from Mg to Sr to Ba. The luminescence lifetimes and quantum yield decrease with the increasing unit cell volume and V-V distance, in the order of Mg3(VO4)2 to Sr3(VO4)2 to Ba3(VO4)2. The emission intensity decreases with the increase of temperatures, but presents no color shift. This confirms that these self-activated M3(VO4)2 phosphors can be suggested as candidates of the single-phase phosphors for light using UV light emitting diodes (LEDs).

  15. OXYGEN TRANSPORT CERAMIC MEMBRANES

    Energy Technology Data Exchange (ETDEWEB)

    Dr. Sukumar Bandopadhyay; Dr. Nagendra Nagabhushana

    2000-10-01

    This is the third quarterly report on oxygen Transport Ceramic Membranes. In the following, the report describes the progress made by our university partners in Tasks 1 through 6, experimental apparatus that was designed and built for various tasks of this project, thermodynamic calculations, where applicable and work planned for the future. (Task 1) Design, fabricate and evaluate ceramic to metal seals based on graded ceramic powder/metal braze joints. (Task 2) Evaluate the effect of defect configuration on ceramic membrane conductivity and long term chemical and structural stability. (Task 3) Determine materials mechanical properties under conditions of high temperatures and reactive atmospheres. (Task 4) Evaluate phase stability and thermal expansion of candidate perovskite membranes and develop techniques to support these materials on porous metal structures. (Task 5) Assess the microstructure of membrane materials to evaluate the effects of vacancy-impurity association, defect clusters, and vacancy-dopant association on the membrane performance and stability. (Task 6) Measure kinetics of oxygen uptake and transport in ceramic membrane materials under commercially relevant conditions using isotope labeling techniques.

  16. Heart rate during basketball game play and volleyball drills accurately predicts oxygen uptake and energy expenditure.

    Science.gov (United States)

    Scribbans, T D; Berg, K; Narazaki, K; Janssen, I; Gurd, B J

    2015-09-01

    There is currently little information regarding the ability of metabolic prediction equations to accurately predict oxygen uptake and exercise intensity from heart rate (HR) during intermittent sport. The purpose of the present study was to develop and, cross-validate equations appropriate for accurately predicting oxygen cost (VO2) and energy expenditure from HR during intermittent sport participation. Eleven healthy adult males (19.9±1.1yrs) were recruited to establish the relationship between %VO2peak and %HRmax during low-intensity steady state endurance (END), moderate-intensity interval (MOD) and high intensity-interval exercise (HI), as performed on a cycle ergometer. Three equations (END, MOD, and HI) for predicting %VO2peak based on %HRmax were developed. HR and VO2 were directly measured during basketball games (6 male, 20.8±1.0 yrs; 6 female, 20.0±1.3yrs) and volleyball drills (12 female; 20.8±1.0yrs). Comparisons were made between measured and predicted VO2 and energy expenditure using the 3 equations developed and 2 previously published equations. The END and MOD equations accurately predicted VO2 and energy expenditure, while the HI equation underestimated, and the previously published equations systematically overestimated VO2 and energy expenditure. Intermittent sport VO2 and energy expenditure can be accurately predicted from heart rate data using either the END (%VO2peak=%HRmax x 1.008-17.17) or MOD (%VO2peak=%HRmax x 1.2-32) equations. These 2 simple equations provide an accessible and cost-effective method for accurate estimation of exercise intensity and energy expenditure during intermittent sport.

  17. Positron annihilation in single crystals of TiO2, VO2, Pb, and U

    International Nuclear Information System (INIS)

    Blau, M.

    1982-09-01

    Two positron annihilation set-ups for Doppler broadening correlation measurements are described. The Doppler broadening spectra were measured in different directions of single crystals of TiO 2 and VO 2 , at room temperature. The anisotropy was explained using two models in which the positron behaves as a free or bounded particle, and was related to the effective charge on the oxygen ion. The changes in the spectra in VO 2 , on passing from the insulator to the metal phase, were found to be gradual and small. The results indicate that the main contribution to the metal-insulator transition is due to changes in the relative occupation of the oxygen p-states and not to changes in covalency or screening. Angular correlations were measured in single crystals of lead in three crystallographic directions. The derivatives of the spectra were compared with the Fermi surface obtained from dHvA measurements, using plane-wave electrons. Most of the features of the experimental derivatives were explained with this simple model. Angular correlation measurements were made on single crystals of uranium in two crystallographic directions. The derivates of the spectra were very wide with a few peaks. (Author)

  18. Density functional study of NO adsorption on undefected and oxygen defective Au–BaO(1 0 0) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Añez, Rafael, E-mail: ranez@ivic.gob.ve [Laboratorio de Química Física y Catálisis Computacional, Centro de Química, Instituto Venezolano de Investigaciones Científicas, Apartado, 21827 Caracas (Venezuela, Bolivarian Republic of); Sierraalta, Aníbal; Bastardo, Anelisse [Laboratorio de Química Física y Catálisis Computacional, Centro de Química, Instituto Venezolano de Investigaciones Científicas, Apartado, 21827 Caracas (Venezuela, Bolivarian Republic of); Coll, David [Laboratorio de Físico Química Teórica de Materiales, Centro de Química, Instituto Venezolano de Investigaciones Científicas, Apartado, 21827 Caracas (Venezuela, Bolivarian Republic of); Garcia, Belkis [Instituto Universitario de Tecnología de Valencia IUTVAL, Valencia, Edo. Carabobo (Venezuela, Bolivarian Republic of)

    2014-07-01

    A periodic density functional approach has been used in order to explore the interaction of NO with undoped and Au doped BaO(1 0 0) surface. Due to oxygen vacancies increase the interaction between the doping metal and the surface, F{sub S} and F{sub S}{sup +} vacancies were studied and compared with the results obtained on the undefected doped BaO(1 0 0). Our results indicate that the high basicity of the BaO surface, besides the electron density changes produced by the oxygen vacancies, modify considerably how the Au atom interacts with the surface increasing the ionic character of the interaction. F{sub S} vacancy shows to be a promise center to activate de NO bond on the BaO(1 0 0) surface.

  19. Tungsten oxides. I. Effects of oxygen vacancies and doping on electronic and optical properties of different phases of WO3

    Science.gov (United States)

    Migas, D. B.; Shaposhnikov, V. L.; Rodin, V. N.; Borisenko, V. E.

    2010-11-01

    In this part we present results of our ab initio calculations indicating that dispersion of the bands near the gap region for different phases of WO3 (namely, ɛ-WO3, δ-WO3, γ-WO3, β-WO3, orth-WO3, α-WO3, and hex-WO3) is rather close. The rapid increase in the absorption coefficient starts at the lower energy range for α-WO3 and hex-WO3 than for the other phases in accordance with the calculated band gaps. An oxygen vacancy has turned out to decrease the gap by 0.50 eV and to shift the absorption coefficient to the lower energy range in the room temperature γ-WO3 phase. We have also traced changes caused by molybdenum and sulfur doping of γ-WO3. Only sulfur doped γ-WO3 has been revealed to display the formation of the impurity band along with a sizable reduction in the gap and the shift in the absorption coefficient to the lower energy range.

  20. Oxygen and disorder effect in the magnetic properties of manganite films

    Energy Technology Data Exchange (ETDEWEB)

    Sirena, M. E-mail: sirenam@ib.cnea.gov.ar; Haberkorn, N.; Granada, M.; Steren, L.B.; Guimpel, J

    2004-05-01

    We have made a systematic study of the magnetic properties of low doped manganite films submitted to different oxygenation treatments. We have found that oxygenation dynamics depends critically of the strain field in the sample. The T{sub C} and the Mr increase as the oxygen content is increased. A decrease of the coercive field of the LSMO-STO films was observed, indicating that annealing treatments increase the oxygen content reducing oxygen vacancies.

  1. Oxygen and disorder effect in the magnetic properties of manganite films

    International Nuclear Information System (INIS)

    Sirena, M.; Haberkorn, N.; Granada, M.; Steren, L.B.; Guimpel, J.

    2004-01-01

    We have made a systematic study of the magnetic properties of low doped manganite films submitted to different oxygenation treatments. We have found that oxygenation dynamics depends critically of the strain field in the sample. The T C and the Mr increase as the oxygen content is increased. A decrease of the coercive field of the LSMO-STO films was observed, indicating that annealing treatments increase the oxygen content reducing oxygen vacancies

  2. The oxygen consumption rates of different life stages of the endoparasitic nematode

    Directory of Open Access Journals (Sweden)

    Willie van Aardt

    2010-01-01

    Full Text Available The oxygen consumption rates of different life stages of the endoparasitic nematode, Pratylenchus zeae (Nematoda: Tylenchida during non- and post-anhydrobiosisPratylenchus zeae, widely distributed in tropical and subtropical regions, is an endoparasite in roots of maize and other crop plants. The nematode is attracted to plant roots by CO2 and root exudates and feeds primarily on cells of the root cortex, making channels and openings where the eggs are deposited, with the result that secondary infection occurs due to bacteria and fungi. Nothing is known about the respiration physiology of this nematode and how it manages to survive during dry seasons. To measure the oxygen consumption rate (VO2 of individual P. zeae (less than half a millimeter long, a special measuring technique namely Cartesian diver micro-respirometry was applied. The Cartesian divers were machined from Perspex, and proved to be more accurate to measure VO2 compared with heavier glass divers used in similar experiments on free living nematodes. An accuracy of better than one nanoliter of oxygen consumed per hour was achieved with a single P. zeae inside the diver. Cartesian diver micro-respirometry measurements are based in principle on the manometric changes that occur in a fl otation tube in a manometer set-up when oxygen is consumed by P. zeae and CO2 from the animal is chemically absorbed. VO2 was measured for eggs (length: < 0.05 mm, larvae (length: 0.36 mm and adults (length: 0.47 mm before induction to anhydrobiosis. P. zeae from infected maize roots were extracted and exposed aseptically to in vitro maize root cultures in a grow cabinet at 50 % to 60% relative humidity at 28 ºC using eggs, larvae and adults. VO2 was also measured for post-anhydrobiotic eggs, larvae and adults by taking 50 individuals, eggs and larvae from the culture and placing them in Petri-dishes with 1% agar/water to dry out for 11 days at 28 ºC and 50% relative humidity. The VO2 was measured

  3. Initial Weekly HRV Response is Related to the Prospective Change in VO2max in Female Soccer Players.

    Science.gov (United States)

    Esco, M R; Flatt, A A; Nakamura, F Y

    2016-06-01

    The aim of this study was to determine whether the early response in weekly measures of HRV, when derived from a smartphone application, were related to the eventual change in VO2max following an off-season training program in female soccer athletes. 9 female collegiate soccer players participated in an 11-week off-season conditioning program. In the week immediately before and after the training program, each participant performed a test on a treadmill to determine maximal oxygen consumption (VO2max). Daily measures of the log-transformed root mean square of successive R-R intervals (lnRMSSD) were performed by the participants throughout week 1 and week 3 of the conditioning program. The mean and coefficient of variation (CV) lnRMSSD values of week 1 showed small (r=- 0.13, p=0.74) and moderate (r=0.57, p=0.11), respectively, non-significant correlations to the change in VO2max at the end of the conditioning program (∆VO2max). Significant and near-perfect correlation was found between the change in the weekly mean lnRMSSD values from weeks 1 and 3 (∆lnRMSSDM) and ∆VO2max (r=0.90, p=0.002). The current results have identified that the initial change in weekly mean lnRMSSD from weeks 1 to 3 of a conditioning protocol was strongly associated with the eventual adaptation of VO2max. © Georg Thieme Verlag KG Stuttgart · New York.

  4. Endurance training decreases the non-linearity in the oxygen uptake-power output relationship in humans.

    Science.gov (United States)

    Majerczak, Joanna; Korostynski, Michal; Nieckarz, Zenon; Szkutnik, Zbigniew; Duda, Krzysztof; Zoladz, Jerzy A

    2012-03-01

    In this study, we hypothesized that 5 weeks of cycling endurance training can decrease the magnitude of the non-proportional increase in oxygen uptake (V(O(2))) to power output relationship (V(O(2)) 'excess') at exercise intensities exceeding the lactate threshold (LT). Ten untrained, physically active men performed a bout of incremental cycling exercise until exhaustion before and after training. The mitochondrial DNA copy number, myosin heavy chain composition and content of uncoupling protein 3 and sarcoplasmic reticulum Ca(2+)-ATPases (SERCAs) were analysed in muscle biopsies taken from vastus lateralis before and after training. The training resulted in an enhancement of the power-generating capabilities at maximal oxygen uptake (V(O(2)max)) by ∼7% (P = 0.002) despite there being no changes in V(O(2)max) (P = 0.49). This effect was due to a considerable reduction in the magnitude of the V(O(2)) 'excess' (P 0.05) were found after training. We conclude that the training-induced increase in power-generating capabilities at V(O(2)max) was due to attenuation of the V(O(2)) 'excess' above the LT. This adaptive response seems to be related to the improvement of muscle metabolic stability, as judged by a lowering of plasma ammonia concentration. The enhancement of muscle metabolic stability after training could be caused by a decrease in ATP usage at a given power output owing to downregulation of SERCA2 pumps.

  5. n-VO{sub 2}/p-GaN based nitride–oxide heterostructure with various thickness of VO{sub 2} layer grown by MBE

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Minhuan [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Bian, Jiming, E-mail: jmbian@dlut.edu.cn [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 200050, China (China); Sun, Hongjun; Liu, Weifeng [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Zhang, Yuzhi [Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 200050, China (China); Luo, Yingmin [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

    2016-12-15

    Graphical abstract: The significant influences of VO{sub 2} layer thickness on the structural, electrical and contact properties of the n-VO{sub 2}/p-GaN based nitride-oxide heterostructure were investigated systemically. - Highlights: • High quality VO{sub 2} films with precisely controlled thickness were grown on p-GaN/sapphire substrates by oxide molecular beam epitaxy (O-MBE). • A distinct reversible SMT phase transition was observed for the n-VO{sub 2}/p-GaN based nitride-oxide heterostructure. • The clear rectifying transport characteristics originated from the n-VO{sub 2}/p-GaN interface were demonstrated before and after SMT of the VO{sub 2} over layer. • The XPS analyses confirmed the valence state of V in VO{sub 2} films was principally composed of V{sup 4+} with trace amount of V{sup 5+}. • The design and modulation of the n-VO{sub 2}/p-GaN based heterostructure devices will benefit significantly from these achievements. - Abstract: High quality VO{sub 2} films with precisely controlled thickness were grown on p-GaN/sapphire substrates by oxide molecular beam epitaxy (O-MBE). Results indicated that a distinct reversible semiconductor-to-metal (SMT) phase transition was observed for all the samples in the temperature dependent electrical resistance measurement, and the influence of VO{sub 2} layer thickness on the SMT properties of the as-grown n-VO{sub 2}/p-GaN based nitride-oxide heterostructure was investigated. Meanwhile, the clear rectifying transport characteristics originated from the n-VO{sub 2}/p-GaN interface were demonstrated before and after SMT of the VO{sub 2} over layer, which were attributed to the p-n junction behavior and Schottky contact character, respectively. Moreover, the X-ray photoelectron spectroscopy (XPS) analyses confirmed the valence state of vanadium (V) in VO{sub 2} films was principally composed of V{sup 4+} with trace amount of V{sup 5+}. The design and modulation of the n-VO{sub 2}/p-GaN based heterostructure

  6. Vacancies in thermal equilibrium in Nb

    International Nuclear Information System (INIS)

    Nielsen, B.; Lynn, K.G.; Hurst, J.; Vehanen, A.; Schultz, P.J.

    1985-06-01

    We have measured the diffusion of positrons in Nb(110) in the temperature range from 300K to 2450K utilizing a variable energy positron beam. The purpose was to study the vacancy formation. However, no significant sign of vacancy trapping was observed. This could be due to a high detrapping rate caused by a low positron binding energy or due to a high vacancy formation enthalpy H/sub IV//sup F/. The last possibility is consistent with recent studies of the vacancy migration and with calculation of the positron binding energy. In this case we find the H/sub IV//sup F/ > 3 eV

  7. 7 CFR 1221.105 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS... INFORMATION ORDER Sorghum Promotion, Research, and Information Order Sorghum Promotion, Research, and Information Board § 1221.105 Vacancies. To fill any vacancy occasioned by the death, removal, resignation, or...

  8. Electrochemical catalytic activity of tungsten trioxide- modified graphite felt toward VO2+/VO2+ redox reaction

    International Nuclear Information System (INIS)

    Shen, Yang; Xu, Hongfeng; Xu, Pengcheng; Wu, Xiaoxin; Dong, Yiming; Lu, Lu

    2014-01-01

    A novel graphite felt electrode modified with tungsten trioxide (WO 3 ) was developed to improve the electrochemical performance of graphite felt toward the VO 2 + /VO 2+ redox pair. WO 3 was prepared using a hydrothermal method, and the morphology of WO 3 structures was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical property of WO 3 -modified graphite felt toward VO 2 + /VO 2+ was carefully characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The hydrogen-vanadium redox flow battery (H-VRFB) test indicates that single cells using 1.1 mg cm −2 WO 3 -modified graphite felt exhibited excellent performance at 70 mA cm −2 , and the corresponding coulombic, voltage, and energy efficiencies were 99.1%, 88.66% and 87.86%, respectively

  9. Estimated Prestroke Peak VO2 Is Related to Circulating IGF-1 Levels During Acute Stroke.

    Science.gov (United States)

    Mattlage, Anna E; Rippee, Michael A; Abraham, Michael G; Sandt, Janice; Billinger, Sandra A

    2017-01-01

    Background Insulin-like growth factor-1 (IGF-1) is neuroprotective after stroke and is regulated by insulin-like binding protein-3 (IGFBP-3). In healthy individuals, exercise and improved aerobic fitness (peak oxygen uptake; peak VO 2 ) increases IGF-1 in circulation. Understanding the relationship between estimated prestroke aerobic fitness and IGF-1 and IGFBP-3 after stroke may provide insight into the benefits of exercise and aerobic fitness on stroke recovery. Objective The purpose of this study was to determine the relationship of IGF-1 and IGFBP-3 to estimated prestroke peak VO 2 in individuals with acute stroke. We hypothesized that (1) estimated prestroke peak VO 2 would be related to IGF-1 and IGFBP-3 and (2) individuals with higher than median IGF-1 levels will have higher estimated prestroke peak VO 2 compared to those with lower than median levels. Methods Fifteen individuals with acute stroke had blood sampled within 72 hours of hospital admission. Prestroke peak VO 2 was estimated using a nonexercise prediction equation. IGF-1 and IGFBP-3 levels were quantified using enzyme-linked immunoassay. Results Estimated prestroke peak VO 2 was significantly related to circulating IGF-1 levels (r = .60; P = .02) but not IGFBP-3. Individuals with higher than median IGF-1 (117.9 ng/mL) had significantly better estimated aerobic fitness (32.4 ± 6.9 mL kg -1 min -1 ) than those with lower than median IGF-1 (20.7 ± 7.8 mL kg -1 min -1 ; P = .03). Conclusions Improving aerobic fitness prior to stroke may be beneficial by increasing baseline IGF-1 levels. These results set the groundwork for future clinical trials to determine whether high IGF-1 and aerobic fitness are beneficial to stroke recovery by providing neuroprotection and improving function. © The Author(s) 2016.

  10. A comparison of VO2max and metabolic variables between treadmill running and treadmill skating.

    Science.gov (United States)

    Koepp, Kriston K; Janot, Jeffrey M

    2008-03-01

    The purpose of this study was to determine differences in VO2max and metabolic variables between treadmill running and treadmill skating. This study also examined VO2max responses during a continuous skating treadmill protocol and a discontinuous skating treadmill protocol. Sixteen male high school hockey players, who had a mean age of 16 +/- 1 years and were of an above-average fitness level, participated in this study. All subjects completed 4 exercise trials: a 1-hour skating treadmill familiarization trial, a treadmill running trial, and 2 randomized skating treadmill trials. Minute ventilation (VE), oxygen consumption VO2), carbon dioxide production VCO2), respiratory exchange ratio (RER), and heart rate were averaged every 15 seconds up to VO2max for each exercise test. The results showed that there was a significant difference (P skating treadmill protocol. There was also a significant difference for maximal RER between the discontinuous and continuous skating treadmill protocol and between the discontinuous skating treadmill protocol and running treadmill protocol. In conclusion, the running treadmill elicited a greater VO2max (mL.kg.min) than the skating treadmill did, but when it comes to specificity of ice skating, the skating treadmill may be ideal. Also, there was no significant difference between the discontinuous and continuous skating treadmill protocols. Therefore, a continuous protocol is possible on the skating treadmill without compromising correct skating position and physiologic responses. However, the continuous skating treadmill protocol should undergo validation before other scientists, coaches, and strength and conditioning professionals can apply it correctly.

  11. Microwave-assisted in situ synthesis of reduced graphene oxide-BiVO{sub 4} composite photocatalysts and their enhanced photocatalytic performance for the degradation of ciprofloxacin

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Yan [School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, Zhenjiang, 212013 (China); Sun, Shaofang [School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, Zhenjiang, 212013 (China); School of Environmental Science and Engineering, Chang’an University, Yanta Road 126, Xi’an, 710054 (China); Song, Yang; Yan, Xu [School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, Zhenjiang, 212013 (China); Guan, Weisheng [School of Environmental Science and Engineering, Chang’an University, Yanta Road 126, Xi’an, 710054 (China); Liu, Xinlin [School of Material Science and Engineering, Jiangsu University, Xuefu Road 301, Zhenjiang, 212013 (China); Shi, Weidong, E-mail: swd1978@ujs.edu.cn [School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, Zhenjiang, 212013 (China)

    2013-04-15

    Highlights: ► Microwave-assisted in situ growth of RGO-BiVO{sub 4} composite was proposed. ► A relatively small particle size with organic-additives free. ► Graphene was formed during the microwave-heating by oxygen capture. ► GB-2 sample exhibits the highest CIP degradation ratio (3 times over pure BiVO{sub 4}). ► The enhancements of activities result from the effective charge separation. -- Abstract: To improve the photodegradation efficiency for ciprofloxacin (CIP), a new-type microwave-assisted in situ growth method is developed for the preparation of reduced graphene oxide (RGO) -BiVO{sub 4} composite photocatalysts. The as-produced RGO-BiVO{sub 4} composite photocatalysts show extremely high enhancement of CIP degradation ratio over the pure BiVO{sub 4} photocatalyst under visible light. Specially, the 2 wt% RGO-BiVO{sub 4} composite photocatalyst exhibits the highest CIP degradation ratio (68.2%) in 60 min, which is over 3 times than that (22.7%) of the pure BiVO{sub 4} particles. The enhancement of photocatalytic activities of RGO-BiVO{sub 4} photocatalysts can be attributed to the effective separation of electron–hole pairs rather than the improvement of light absorption.

  12. The role of haemoglobin mass on VO(2)max following normobaric 'live high-train low' in endurance-trained athletes

    DEFF Research Database (Denmark)

    Robach, Paul; Siebenmann, Christoph; Jacobs, Robert A

    2012-01-01

    It remains unclear by which mechanism 'live high-train low' (LHTL) altitude training increases exercise performance. Haematological and skeletal muscle adaptations have both been proposed. To test the hypotheses that (i) LHTL improves maximal oxygen uptake (VO(2)max) and (ii) this improvement is ...

  13. Suppression of oxygen diffusion by thin Al2O3 films grown on SrTiO3 studied using a monoenergetic positron beam

    International Nuclear Information System (INIS)

    Uedono, A.; Kiyohara, M.; Yasui, N.; Yamabe, K.

    2005-01-01

    The annealing behaviors of oxygen vacancies introduced by the epitaxial growth of thin SrTiO 3 and Al 2 O 3 films on SrTiO 3 substrates were studied by using a monoenergetic positron beam. The films were grown by molecular-beam epitaxy without using an oxidant. The Doppler broadening spectra of the annihilation radiation were measured as a function of the incident positron energy for samples fabricated under various growth conditions. The line-shape parameter S, corresponding to the annihilation of positrons in the substrate, was increased by the film growth, suggesting diffusion of oxygen from the substrate into the film and a resultant introduction of vacancies (mainly oxygen vacancies). A clear correlation between the value of S and the substrate conductivity was obtained. From isochronal annealing experiments, the Al 2 O 3 thin film was found to suppress the penetration of oxygen from the atmosphere for annealing temperatures below 600 deg. C. Degradation of the film's oxygen blocking property occurred due to the annealing at 700 deg. C, and this was attributed to the oxidation of the Al 2 O 3 by the atmosphere and the resultant introduction of vacancy-type defects

  14. Phosphorous–vacancy–oxygen defects in silicon

    KAUST Repository

    Wang, Hao

    2013-07-30

    Electronic structure calculations employing the hybrid functional approach are used to gain fundamental insight in the interaction of phosphorous with oxygen interstitials and vacancies in silicon. It recently has been proposed, based on a binding energy analysis, that phosphorous–vacancy–oxygen defects may form. In the present study we investigate the stability of this defect as a function of the Fermi energy for the possible charge states. Spin polarization is found to be essential for the charge neutral defect.

  15. Effects of grain boundaries at the electrolyte/cathode interfaces on oxygen reduction reaction kinetics of solid oxide fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Min Gi; Koo, Ja Yang; Ahn, Min Woo; Lee, Won Young [Dept. of Mechanical Engineering, Sungkyunkwan University, Suwon (Korea, Republic of)

    2017-04-15

    We systematically investigated the effects of grain boundaries (GBs) at the electrolyte/cathode interface of two conventional electrolyte materials, i.e., yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC). We deposited additional layers by pulsed laser deposition to control the GB density on top of the polycrystalline substrates, obtaining significant improvements in peak power density (two-fold for YSZ and three-fold for GDC). The enhanced performance at high GB density in the additional layer could be ascribed to the accumulation of oxygen vacancies, which are known to be more active sites for oxygen reduction reactions (ORR) than grain cores. GDC exhibited a higher enhancement than YSZ, due to the easier formation, and thus higher concentration, of oxygen vacancies for ORR. The strong relation between the concentration of oxygen vacancies and the surface exchange characteristics substantiated the role of GBs at electrolyte/cathode interfaces on ORR kinetics, providing new design parameters for highly performing solid oxide fuel cells.

  16. Changing vacancy balance in ZnO by tuning synthesis between zinc/oxygen lean conditions

    Science.gov (United States)

    Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas; Zubiaga, Asier; Tuomisto, Filip; Kuznetsov, Andrej Yu.

    2010-08-01

    The nature of intrinsic defects in ZnO films grown by metal organic vapor phase epitaxy was studied by positron annihilation and photoluminescence spectroscopy techniques. The supply of Zn and O during the film synthesis was varied by applying different growth temperatures (325-485 °C), affecting decomposition of the metal organic precursors. The microscopic identification of vacancy complexes was derived from a systematic variation in the defect balance in accordance with Zn/O supply trends.

  17. Surface oxygen vacancy and oxygen permeation flux limits of perovskite ion transport membranes

    KAUST Repository

    Hunt, Anton; Dimitrakopoulos, Georgios; Ghoniem, Ahmed F.

    2015-01-01

    © 2015 Elsevier B.V. The mechanisms and quantitative models for how oxygen is separated from air using ion transport membranes (ITMs) are not well understood, largely due to the experimental complexity for determining surface exchange reactions

  18. Hydrogen isotope in erbium oxide: Adsorption, penetration, diffusion, and vacancy trapping

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Wei, E-mail: mao@nuclear.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan); Chikada, Takumi [Department of Chemistry, Graduate School of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529 (Japan); Suzuki, Akihiro [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22, Shirakata-shirane, Tokai, Naka 319-1188, Ibaraki (Japan); Terai, Takayuki [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Matsuzaki, Hiroyuki [The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan)

    2015-03-15

    Highlights: • H adsorption on cubic Er{sub 2}O{sub 3} surface results in electron transfer from H to the surface. • The H penetration energy of at least 1.6 eV is required for cubic Er{sub 2}O{sub 3} surface. • The dominated mechanisms of H diffusion in bulk Er{sub 2}O{sub 3} are elucidated. • H diffusion near or at vacancies in Er{sub 2}O{sub 3} is an exothermic reaction. - Abstract: In this study, we report results using first-principles density functional theory calculations for four critical aspects of the interaction: H adsorption on Er{sub 2}O{sub 3} surface, surface-to-subsurface penetration of H into Er{sub 2}O{sub 3}, bulk diffusion of H in Er{sub 2}O{sub 3}, and trapping of H at vacancies. We identify surface stable adsorption positions and find that H prefers to transfer electrons to the surfaces and form covalent bonds with the nearest neighboring four oxygen atoms. For low surface coverage of H as in our case (0.89 × 10{sup 14} H/cm{sup 2}), a penetration energy of at least 1.60 eV is required for cubic Er{sub 2}O{sub 3} surfaces. Further, the H diffusion barrier between the planes defined by Er{sub 2}O{sub 3} units along the favorable <1 1 1> direction is found to be very small – 0.16 eV – whereas higher barriers of 0.41 eV and 1.64 eV are required for diffusion across the planes, somewhat higher than the diffusion energy barrier of 0.20 eV observed experimentally at 873 K. In addition, we predict that interstitial H is exothermically trapped when it approaches a vacancy with the vacancy defect behaving as an electron trap since the H-vacancy defect is found to be more stable than the intrinsic defect.

  19. Determinants of maximal oxygen uptake in severe acute hypoxia

    DEFF Research Database (Denmark)

    Calbet, J A L; Boushel, Robert Christopher; Rådegran, G

    2003-01-01

    To unravel the mechanisms by which maximal oxygen uptake (VO2 max) is reduced with severe acute hypoxia in humans, nine Danish lowlanders performed incremental cycle ergometer exercise to exhaustion, while breathing room air (normoxia) or 10.5% O2 in N2 (hypoxia, approximately 5,300 m above sea......: 1) reduction of PiO2, 2) impairment of pulmonary gas exchange, and 3) reduction of maximal cardiac output and peak leg blood flow, each explaining about one-third of the loss in VO2 max....

  20. Allometric modelling of peak oxygen uptake in male soccer players of 8-18 years of age

    NARCIS (Netherlands)

    Valente-dos-Santos, Joao; Coelho-e-Silva, Manuel J.; Tavares, Oscar M.; Brito, Joao; Seabra, Andre; Rebelo, Antonio; Sherar, Lauren B.; Elferink-Gemser, Marije T.; Malina, Robert M.

    Background: Peak oxygen uptake (VO2peak) is routinely scaled as mL O-2 per kilogram body mass despite theoretical and statistical limitations of using ratios. Aim: To examine the contribution of maturity status and body size descriptors to ageassociated inter-individual variability in VO2peak and to

  1. Diffusion in a pure, high-vacancy-content crystal

    International Nuclear Information System (INIS)

    McKee, R.A.

    1981-01-01

    The idea that vacancies can follow a nonrandom walk in a solid has been developed and put into a quantitative form for diffusion in a pure, high-vacancy-content crystal. Intrinsic and tracer diffusion in a metal have been analyzed, and the electrical mobility in an ionic solid has been expressed in terms of the tracer diffusion coefficient and the separate correlation factors for atoms and vacancies. The description uses classical methods of diffusion theory, and generalized results that account for nonrandom vacancy walk have been shown to reduce to those obtained by Howard and Lidiard in a system where the vacancy moves randomly as an isolated point defect. Experimental data for carbon diffusion in fcc iron have been examined to illustrate an interstitial-vacancy analogy that was used in this analysis, and the general result has been applied specifically to discuss vacancy diffusion in Fe/sub 1-x/S

  2. Machine learning and statistical methods for the prediction of maximal oxygen uptake: recent advances.

    Science.gov (United States)

    Abut, Fatih; Akay, Mehmet Fatih

    2015-01-01

    Maximal oxygen uptake (VO2max) indicates how many milliliters of oxygen the body can consume in a state of intense exercise per minute. VO2max plays an important role in both sport and medical sciences for different purposes, such as indicating the endurance capacity of athletes or serving as a metric in estimating the disease risk of a person. In general, the direct measurement of VO2max provides the most accurate assessment of aerobic power. However, despite a high level of accuracy, practical limitations associated with the direct measurement of VO2max, such as the requirement of expensive and sophisticated laboratory equipment or trained staff, have led to the development of various regression models for predicting VO2max. Consequently, a lot of studies have been conducted in the last years to predict VO2max of various target audiences, ranging from soccer athletes, nonexpert swimmers, cross-country skiers to healthy-fit adults, teenagers, and children. Numerous prediction models have been developed using different sets of predictor variables and a variety of machine learning and statistical methods, including support vector machine, multilayer perceptron, general regression neural network, and multiple linear regression. The purpose of this study is to give a detailed overview about the data-driven modeling studies for the prediction of VO2max conducted in recent years and to compare the performance of various VO2max prediction models reported in related literature in terms of two well-known metrics, namely, multiple correlation coefficient (R) and standard error of estimate. The survey results reveal that with respect to regression methods used to develop prediction models, support vector machine, in general, shows better performance than other methods, whereas multiple linear regression exhibits the worst performance.

  3. HYDROGEN VACANCY INTERACTION IN TUNGSTEN

    NARCIS (Netherlands)

    FRANSENS, [No Value; ELKERIEM, MSA; PLEITER, F

    1991-01-01

    Hydrogen-vacancy interaction in tungsten was investigated by means of the perturbed angular correlation technique, using the isotope In-111 as a probe. Hydrogen trapping at an In-111-vacancy cluster manifests itself as a change of the local electric field gradient, which gives rise to an observable

  4. Oxygen consumption of elite distance runners on an anti-gravity treadmill®.

    Science.gov (United States)

    McNeill, David K P; Kline, John R; de Heer, Hendrick D; Coast, J Richard

    2015-06-01

    Lower body positive pressure (LBPP), or 'anti-gravity' treadmills® have become increasingly popular among elite distance runners. However, to date, few studies have assessed the effect of body weight support (BWS) on the metabolic cost of running among elite runners. This study evaluated how BWS influenced the relationship between velocity and metabolic cost among 6 elite male distance runners. Participants ran three- 16 minute tests consisting of 4 stages of 4 minutes at 8, 7, 6 and 5 min·mile(-1) pace (3.35, 3.84, 4.47 and 5.36 m·s(-1)), while maintaining an aerobic effort (Respiratory Exchange Ratio ≤1.00). One test was run on a regular treadmill, one on an anti-gravity treadmill with 40% BWS and one with 20% BWS being provided. Expired gas data were collected and regression equations used to determine and compare slopes. Significant decreases in oxygen uptake (V̇O2) were found with each increase in BWS (p rate, perceived exertion or directly measured oxygen uptake) should be used to guide training intensity when training on the LBPP treadmill. Key pointsWith increasing amounts of body weight-support (BWS), the slope of the relationship between velocity and oxygen consumption (ΔVO2/Δv) decreases significantly. This means the change in oxygen consumption (VO2) is significantly smaller over a given change in velocity at higher amounts of BWS.There is a non-linear decrease in VO2 with increasing BWS. As such, with each increment in the amount of BWS provided, the reduction in VO2 becomes increasingly smaller.This paper provides first of its kind data on the effects of BWS on the cost of running among highly trained, elite runners. The outcomes of this study are in line with previous findings among non-elite runners.

  5. Exercise-induced prostacyclin release positively correlates with VO(2max) in young healthy men.

    Science.gov (United States)

    Zoladz, J A; Majerczak, J; Duda, K; Chłopicki, S

    2009-01-01

    In this study we have evaluated the effect of maximal incremental cycling exercise (IE) on the systemic release of prostacyclin (PGI(2)), assessed as plasma 6-keto-PGF(1alpha) concentration in young healthy men. Eleven physically active - untrained men (mean +/- S.D.) aged 22.7 +/- 2.1 years; body mass 76.3 +/- 9.1 kg; BMI 23.30 +/- 2.18 kg . m(-2); maximal oxygen uptake (VO(2max)) 46.5 +/- 3.9 ml . kg(-1) . min(-1), performed an IE test until exhaustion. Plasma concentrations of 6-keto-PGF(1alpha), lactate, and cytokines were measured in venous blood samples taken prior to the exercise and at the exhaustion. The net exercise-induced increase in 6-keto-PGF(1alpha) concentration, expressed as the difference between the end-exercise minus pre-exercise concentration positively correlated with VO(2max) (r=0.78, p=0.004) as well as with the net VO(2) increase at exhaustion (r=0.81, p=0.003), but not with other respiratory, cardiac, metabolic or inflammatory parameters of the exercise (minute ventilation, heart rate, plasma lactate, IL-6 or TNF-alpha concentrations). The exercise-induced increase in 6-keto-PGF(1alpha) concentration?? was significantly higher (p=0.008) in a group of subjects (n=5) with the highest VO(2max) when compared to the group of subjects with the lowest VO(2max), in which no increase in 6-keto-PGF(1alpha) concentration was found. In conclusion, we demonstrated, to our knowledge for the first time, that exercise-induced release of PGI(2) in young healthy men correlates with VO(2max), suggesting that vascular capacity to release PGI(2) in response to physical exercise represents an important factor characterizing exercise tolerance. Moreover, we postulate that the impairment of exercise-induced release of PGI(2) leads to the increased cardiovascular hazard of vigorous exercise.

  6. Klasični (ekstenzivni) voćnjaci u Hrvatskoj

    OpenAIRE

    Čmelik, Zlatko

    2011-01-01

    Hrvatska ima vrlo povoljne pomoekološke uvjete za uzgoj voćaka. Tradicija uzgoja voćaka duga je više stoljeća, a voćke su se uzgajale na gotovo svim seoskim gospodarstvima, te dijelom i u urbanim sredinama. Intenzivan uzgoj voćaka počeo se značajnije širiti polovinom prošlog stoljeća. Intenzivan uzgoj je u određenoj mjeri potisnuo interes za klasičnim, ali se postojeći voćnjaci visokostablašica uglavnom nisu krčili već su u većoj mjeri bili zapušteni. U novije vrijeme klasični voćnjaci pon...

  7. Variação diurna e resposta da cinética do VO2 de ciclistas durante exercício muito intenso Diurnal variation and Vo2 kinetic response of cyclists during heavy exercis e

    Directory of Open Access Journals (Sweden)

    Marcos G. Santana

    2008-06-01

    Full Text Available O objetivo do presente estudo foi avaliar a influência da hora do dia nos parâmetros da cinética do consumo de oxigênio de ciclistas durante exercício muito intenso. Nove voluntários do sexo masculino realizaram exercícios de carga constante às 08:00, 13:00 e 18:00 h, em dias diferentes. Estes exercícios foram realizados duas vezes em cada visita, com um intervalo de 1 h entre eles. A intensidade usada foi de 75%Δ (75% da diferença entre o VO2 no limiar de lactato e o VO2max. A amplitude do componente primário do VO2 (2597 ± 273 ml.min-1, 2513 ± 268 ml.min-1 e 2609 ± 370 ml.min-1, a constante de tempo do componente primário do VO2 (19.3 ± 2.5 s, 18.4 ± 3.0 s e 19.7 ± 3.9 s, o componente lento do VO2 (735 ± 81 ml.min-1, 764 ± 99 ml.min-1 e 680 ± 121 ml.min-1 e o tempo de resposta média (51.8 ± 4.2 s, 51.2 ± 4.2 s e 51.4 ± 3.4 s não apresentaram diferenças significativas entre os diferentes horários do dia (08:00, 13:00 e 18:00 h, assim como os demais parâmetros da cinética do VO2. Estes resultados sugerem que a resposta da cinética do VO2 de ciclistas durante exercício muito intenso (75%Δ não é influenciada pela hora do dia.The objective of the present study was to evaluate the influence of the time of day on the parameters of oxygen uptake kinetics of trained cyclists during high intensity exercise. Nine male volunteers repeated bouts at constant loads at 08:00, 13:00 and 18:00 h on different days. These exercise bouts were performed twice on each occasion, with an interval of 1 h between them. The load intensity used was 75%Δ (75% of the difference between the VO2 at the lactate threshold and the VO2max. The primary VO2 amplitude (2597 ± 273 ml.min-1, 2513 ± 268 ml.min-1 and 2609 ± 370 ml.min-1, the primary VO2 time constant (19.3 ± 2.5 s, 18.4 ± 3.0 s and 19.7 ± 3.9 s, the VO2 slow component (735 ± 81 ml.min-1, 764 ± 99 ml.min-1 and 680 ± 121 ml.min-1 and the mean response time (51.8 ± 4.2 s, 51

  8. Oxygen uptake kinetics during and after exercise are useful markers of coronary artery disease in patients with exercise electrocardiography suggesting myocardial ischemia

    International Nuclear Information System (INIS)

    Tajima, Akihiko; Ohkoshi, Nobuyuki; Kawara, Tokuhiro; Aizawa, Tadanori; Itoh, Haruki; Maeda, Tomoko; Osada, Naohiko; Omiya, Kazuto; Wasserman, K.

    2009-01-01

    The aim of the current study was to determine if the slowed exercise oxygen uptake (VO 2 ) kinetics, which is developed by myocardial ischemia, would be accompanied by delayed recovery VO 2 kinetics in patients with coronary artery disease (CAD). Thirty-seven patients with significant ST depression during treadmill exercise underwent cardiopulmonary exercise testing with cycle ergometer. Measurements performed are the ratios of change in increase in oxygen (O 2 ) uptake relative to increase in work rate (ΔVO 2 /ΔWR) across anaerobic threshold (AT) and 1 mm ST depression point (ST-dep), the time constants of VO 2 during recovery (T 1/2 VO 2 ), stress radio-isotope scintigraphy and coronary angiography. Patients were divided into CAD positive (CAD+) and CAD negative (CAD-) groups, based on coronary angiography. In CAD+, ΔVO 2 /ΔWR decreased above AT and ST-dep, in contrast to CAD- patients. The T 1/2 VO 2 in CAD+ (103.1±13.0 s) was greater than that of CAD- (76.5±8.7 s) and showed negative correlations to the ratios of ΔVO 2 /ΔWR across AT and ST-dep. These parameters improved in the patients who underwent coronary bypass surgery. Exercise and recovery VO 2 kinetics were slowed when myocardial ischemia was provoked by exercise. Measurement of exercise and recovery VO 2 kinetics improve the accuracy of the exercise electrocardiogram diagnosis of CAD. (author)

  9. Surfactant-assisted hydrothermal fabrication and visible-light-driven photocatalytic degradation of methylene blue over multiple morphological BiVO4 single-crystallites

    International Nuclear Information System (INIS)

    Meng Xue; Zhang Lei; Dai Hongxing; Zhao Zhenxuan; Zhang Ruzhen; Liu Yuxi

    2011-01-01

    Monoclinic BiVO 4 single-crystallites with polyhedral, rod-like, tubular, leaf-like, and spherical morphologies have been fabricated using the triblock copolymer P123-assisted hydrothermal strategy with bismuth nitrate and ammonium metavanadate as metal source and various bases as pH adjustor. The physicochemical properties of the materials were characterized by means of the XRD, TGA/DSC, Raman, HRSEM, HRTEM/SAED, XPS, and UV-vis techniques. The photocatalytic activities of the as-fabricated BiVO 4 samples were measured for the photodegradation of methylene blue (MB) under visible-light irradiation. It is shown that factors, such as the pH value of precursor solution, the introduction of surfactant, the nature of alkaline source, and the hydrothermal temperature, have a crucial influence on the particle architecture of the BiVO 4 product. Among the as-fabricated BiVO 4 samples, the ones derived hydrothermally with P123 at pH = 6 or 10 possessed excellent optical absorption performance both in UV- and visible-light regions and hence showed outstanding photocatalytic activities for the addressed reaction. The unusually high visible-light-driven catalytic performance of monoclinically crystallized rod-like and tubular BiVO 4 single-crystallites is associated with the higher surface areas and concentrations of surface oxygen defects, and unique particle morphologies. The possible formation mechanisms of such multiple morphological BiVO 4 materials have also been discussed.

  10. Oxygen delivery and consumption during on-bypass cabg in htea and central analgesia

    Directory of Open Access Journals (Sweden)

    Віталій Олексійович Собокарь

    2015-04-01

    Full Text Available Objective. Despite some advantages, the use of high thoracic epidural anesthesia (HTEA during on-bypass cardiac surgery may be discouraged by fear of adverse hemodynamic effects and associated disturbances of oxygen delivery.Aim. To compare oxygen delivery and consumption during on-bypass coronary artery bypass grafting in settings of HTEA and central analgesia (CA.Methods. 132 patients were assigned into two groups – study group (n=85, where the surgery was performed under HTEA and control group (n=47 - where the surgery was carried out under CA. Using data of transesophageal cardiac ultrasound and blood oximetry blood oxygen delivery (DO2, oxygen consumption (VO2, oxygen extraction coefficient (CEO2 were calculated at four stages of the surgery: after induction, sternotomy, cardiopulmonary bypass and at the end of the surgery.Results. In the initial stages of the surgery DO2 and VO2 were reduced relative to reference values with a tendency to increase in the course of the operation and achievement of the normal or supernormal level (VO2, study group in the final stage. The decrease was due to moderate hypodynamic circulation and hemodilution. After sternotomy DO2 in the study group was higher than that of the control: 356 (279; 458 vs 317±89 ml·min-1·m-2, (р=0,021. After cardiopulmonary bypass oxygen saturation of venous blood (SatvO2, in the study group was 71 ± 9 % compared with 68 ± 10 % in the control group. At the end of the surgery SatvO2 in the study group was 71 (66; 75 vs 59 (53; 70 % in the control (р = 0,005 and oxygen tension of venous blood (РvО2 was correspondingly 39 ± 6 and 33 (30; 38 mm Hg (р = 0,027. Despite the decrease in DO2 and VO2, oxygen extraction indices - CEO2, pvO2, SatvO2, and remained within the reference range, except that of the control group at the end of the surgery. Furthermore, at no stage lactate rise or acid-base deviations was observed in the both groups.Conclusions. In patients operated

  11. A close correlation between induced ferromagnetism and oxygen deficiency in Fe doped In2O3

    International Nuclear Information System (INIS)

    Singhal, R.K.; Samariya, A.; Kumar, Sudhish; Sharma, S.C.; Xing, Y.T.; Deshpande, U.P.; Shripathi, T.; Saitovitch, E.

    2010-01-01

    We report on the reversible manipulation of room temperature ferromagnetism in Fe (5%) doped In 2 O 3 polycrystalline magnetic semiconductor. The X-ray diffraction and photoemission measurements confirm that the Fe ions are well incorporated into the lattice, substituting the In 3+ ions. The magnetization measurements show that the host In 2 O 3 has a diamagnetic ground state, while it shows weak ferromagnetism at 300 K upon Fe doping. The as-prepared sample was then sequentially annealed in hydrogen, air, vacuum and finally in air. The ferromagnetic signal shoots up by hydrogenation as well as vacuum annealing and bounces back upon re-annealing the samples in air. The sequence of ferromagnetism shows a close inter-relationship with the behavior of oxygen vacancies (V o ). The Fe ions tend to a transform from 3+ to 2+ state during the giant ferromagnetic induction, as revealed by photoemission spectroscopy. A careful characterization of the structure, purity, magnetic, and transport properties confirms that the ferromagnetism is due to neither impurities nor clusters but directly related to the oxygen vacancies. The ferromagnetism can be reversibly controlled by these vacancies while a parallel variation of carrier concentration, as revealed by resistance measurements, appears to be a side effect of the oxygen vacancy variation.

  12. Vacancy complexes induce long-range ferromagnetism in GaN

    KAUST Repository

    Zhang, Zhenkui

    2014-11-14

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μB, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  13. Vacancy complexes induce long-range ferromagnetism in GaN

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhenkui; Schwingenschlögl, Udo, E-mail: Udo.Schwingenschlogl@kaust.edu.sa, E-mail: Iman.Roqan@kaust.edu.sa; Roqan, Iman S., E-mail: Udo.Schwingenschlogl@kaust.edu.sa, E-mail: Iman.Roqan@kaust.edu.sa [Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia)

    2014-11-14

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μ{sub B}, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  14. Vacancy complexes induce long-range ferromagnetism in GaN

    KAUST Repository

    Zhang, Zhenkui; Schwingenschlö gl, Udo; Roqan, Iman S.

    2014-01-01

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μB, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  15. Vacancy decay in endohedral atoms

    International Nuclear Information System (INIS)

    Amusia, M. Ya.; Baltenkov, A. S.

    2006-01-01

    It is demonstrated that the fullerene shell dramatically affects the radiative and Auger vacancy decay of an endohedral atom A-C 60 . The collectivized electrons of the C 60 shell add new possibilities for radiative and nonradiative decays similar to that in ordinary atoms where the vacancies in the initial and final state almost always belong to different subshells. It is shown that the smallness of the atomic shell radii as compared to that of the fullerene shell provides an opportunity to derive the simple formulas for the probabilities of the electron transitions. It is shown that the radiative and Auger (or Koster-Kronig) widths of the vacancy decay due to electron transition in the atom A in A-C 60 acquire an additional factor that can be expressed via the polarizability of the C 60 at transition energy. It is demonstrated that due to an opening of the nonradiative decay channel for vacancies in subvalent subshells the decay probability increases by five to six orders of magnitude

  16. Predição da potência aeróbia (VO2máx de crianças e adolescentes em teste incremental na esteira rolante Prediction of aerobic power (VO2max of children and adolescents during an incremental treadmill test

    Directory of Open Access Journals (Sweden)

    Fabiana Andrade Machado

    2013-03-01

    Full Text Available O consumo máximo de oxigênio (VO2máx é a quantidade máxima de energia que pode ser produzida pelo metabolismo aeróbio em determinada unidade de tempo, podendo ser determinado direta ou indiretamente através de equações preditivas. O objetivo deste trabalho foi elaborar uma equação preditiva específica para determinar o VO2máx de meninos de 10 a 16 anos. Quarenta e dois meninos realizaram teste ergoespirométrico de corrida em esteira rolante com velocidade inicial de 9 km/h até exaustão voluntária. Através da regressão linear múltipla foi possível desenvolver a seguinte equação para a determinação indireta do VO2máx: VO2máx (ml/min = -1574,06 + (141,38 x Vpico + (48,34 * Massa corporal, com erro padrão de estimativa = 191,5 ml/min (4,10 ml/kg/min e o coeficiente de determinação = 0,934. Sugerimos que esta é uma fórmula adequada para predizer o VO2máx para esta população.The maximal oxygen uptake (VO2max is the maximal quantity of energy that can be produced by the aerobic metabolism in certain time unity. It can be determined direct or indirectly by predictive equations. The objective of this study was to make a specific predictive equation to determine the VO2max from boys aged 10-16 years-old. Forty-two boys underwent a treadmill running ergospirometric test, with the initial velocity set at 9 km/h, until voluntary exhaustion. By the multiple linear regression was possible to develop the following equation for the indirect determination of the VO2max: VO2max (ml/min = -1574.06 + (141.38 x Vpeak + (48.34 * Body mass, with standard error of estimate = 191.5 ml/min (4.10 ml/kg/min and coefficient of determination = 0.934. We suggest that this formula is appropriate to predict VO2max for this population.

  17. Remarkable changes in interface O vacancy and metal-oxide bonds in amorphous indium-gallium-zinc-oxide thin-film transistors by long time annealing at 250 °C

    International Nuclear Information System (INIS)

    Chowdhury, Md Delwar Hossain; Um, Jae Gwang; Jang, Jin

    2014-01-01

    We have studied the effect of long time post-fabrication annealing on negative bias illumination stress (NBIS) of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film-transistors. Annealing for 100 h at 250 °C increased the field effect mobility from 14.7 cm 2 /V s to 17.9 cm 2 /V s and reduced the NBIS instability remarkably. Using X-ray photoelectron spectroscopy, the oxygen vacancy and OH were found to exist at the interfaces of a-IGZO with top and bottom SiO 2 . Long time annealing helps to decrease the vacancy concentration and increase the metal-oxygen bonds at the interfaces; this leads to increase in the free carrier concentrations in a-IGZO and field-effect mobility. X-ray reflectivity measurement indicated the increment of a-IGZO film density of 5.63 g cm −3 to 5.83 g cm −3 (3.4% increase) by 100 h annealing at 250 °C. The increase in film density reveals the decrease of O vacancy concentration and reduction of weak metal-oxygen bonds in a-IGZO, which substantially helps to improve the NBIS stability

  18. Role of vacancy defects in Al doped ZnO thin films for optoelectronic devices

    Science.gov (United States)

    Rotella, H.; Mazel, Y.; Brochen, S.; Valla, A.; Pautrat, A.; Licitra, C.; Rochat, N.; Sabbione, C.; Rodriguez, G.; Nolot, E.

    2017-12-01

    We report on the electrical, optical and photoluminescence properties of industry-ready Al doped ZnO thin films grown by physical vapor deposition, and their evolution after annealing under vacuum. Doping ZnO with Al atoms increases the carrier density but also favors the formation of Zn vacancies, thereby inducing a saturation of the conductivity mechanism at high aluminum content. The electrical and optical properties of these thin layered materials are both improved by annealing process which creates oxygen vacancies that releases charge carriers thus improving the conductivity. This study underlines the effect of the formation of extrinsic and intrinsic defects in Al doped ZnO compound during the fabrication process. The quality and the optoelectronic response of the produced films are increased (up to 1.52 mΩ \\cdotcm and 3.73 eV) and consistent with the industrial device requirements.

  19. Increased cardiac output and maximal oxygen uptake in response to ten sessions of high intensity interval training.

    Science.gov (United States)

    Astorino, Todd A; Edmunds, Ross M; Clark, Amy; King, Leesa; Gallant, Rachael M; Namm, Samantha; Fischer, Anthony; Wood, Kimi A

    2018-01-01

    Increases in maximal oxygen uptake (VO2max) are widely reported in response to completion of high intensity interval training (HIIT), yet the mechanism explaining this result is poorly understood. This study examined changes in VO2max and cardiac output (CO) in response to 10 sessions of low-volume HIIT. Participants included 30 active men and women (mean age and VO2max=22.9±5.4 years and 39.6±5.6 mL/kg/min) who performed HIIT and 30 men and women (age and VO2max=25.7±4.5 years and 40.7±5.2 mL/kg/min) who served as non-exercising controls (CON). High intensity interval training consisted of 6-10 s bouts of cycling per session at 90-110 percent peak power output (PPO) interspersed with 75 s recovery. Before and after training, progressive cycling to exhaustion was completed during which CO, stroke volume (SV), and heart rate (HR) were estimated using thoracic impedance. To confirm VO2max attainment, a verification test was completed after progressive cycling at a work rate equal to 110%PPO. Data demonstrated significant improvements in VO2max (2.71±0.63 L/min to 2.86±0.63 L/min, Psessions of HIIT is due to improvements in oxygen delivery.

  20. Topotactic insertion of lithium in the layered structure Li4VO(PO4)2: The tunnel structure Li5VO(PO4)2

    International Nuclear Information System (INIS)

    Satya Kishore, M.; Pralong, V.; Caignaert, V.; Malo, S.; Hebert, S.; Varadaraju, U.V.; Raveau, B.

    2008-01-01

    A new V(III) lithium phosphate Li 5 VO(PO 4 ) 2 has been synthesized by electrochemical insertion of lithium into Li 4 VO(PO 4 ) 2 . This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li 4 VO(PO 4 ) 2 and to the tunnel structure of VO(H 2 PO 4 ) 2 . The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H 2 PO 4 ) 2 and going to the final phase Li 5 VO(PO 4 ) 2 are explained on the basis of the flexible coordinations of V 4+ and V 3+ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality. - Graphical abstract: Electrochemical synthesis of a new 3D V(III) lithium phosphate, Li 5 VO(PO 4 ) 2 . Starting from the 2D Li 4 VO(PO 4 ) 2 , the topotactic reaction that take place during lithium intercalation is explained on the basis of the flexible coordinations of V 4+ and V 3+ species

  1. Direct observation of hopping induced spin polarization current in oxygen deficient Co-doped ZnO by Andreev reflection technique

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Kung-Shang; Huang, Tzu-Yu; Dwivedi, G.D. [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China); Lin, Lu-Kuei; Lee, Shang-Fan [Taiwan Institute of Physics, Academia Sinica, Taipei, Taiwan (China); Sun, Shih-Jye [Department of Applied Physics, National Kaohsiung University, Kaohsiung, Taiwan (China); Chou, Hsiung, E-mail: hchou@mail.nsysu.edu.tw [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China)

    2017-07-01

    Highlights: • Co-doped ZnO thin-films were grown with varying V{sub O} concentartion. • PCAR measurements were done to study the SPC. • High spin polarization was observed above a certain V{sub O} concentartion. • High V{sub O} samples provide a high density of completed percolation path. • This complete percolation path gives rise to high SPC. - Abstract: Oxygen vacancy induced ferromagnetic coupling in diluted magnetic oxide (DMO) semiconductors have been reported in several studies, but technologically more crucial spin-polarized current (SPC) is still under-developed in DMOs. Few studies have claimed that VRH mechanism can originate the SPC, but, how VRH mechanism associated with percolation path, is not clearly understood. We used Point-contact Andreev reflection (PCAR) technique to probe the SPC in Co-doped ZnO (CZO) films. Since the high resistance samples cause broadening in conductance(G)-voltage(V) curves, which may result in an unreliable evaluation of spin polarization, we include two extra parameters, (i) effective temperature and (ii) spreading resistance, for the simulation to avoid the uncertainty in extracting spin polarization. The effective G-V curves and higher spin polarization can be obtained above a certain oxygen vacancy concentration. The number of completed and fragmentary percolation paths is proportional to the concentration of oxygen vacancies. For low oxygen vacancy samples, the Pb-tip has a higher probability of covering fragmentary percolation paths than the complete ones, due to its small contact size. The completed paths may remain independent of one another and get polarized in different directions, resulting in lower spin-polarization value. High oxygen vacancy samples provide a high density of completed path, most of them link to one another by crossing over, and gives rise to high spin-polarization value.

  2. Exploring and Controlling Intrinsic Defect Formation in SnO2 Thin Films

    KAUST Repository

    Porte, Yoann; Maller, Robert; Faber, Hendrik; Alshareef, Husam N.; Anthopoulos, Thomas D; McLachlan, Martyn

    2015-01-01

    By investigating the influence of key growth variables on the measured structural and electrical properties of SnO2 prepared by Pulsed Laser Deposition (PLD) we demonstrate fine control of intrinsic n-type defect formation. Variation of growth temperatures shows oxygen vacancies (VO) as the dominant defect which can be compensated for by thermal oxidation at temperatures > 500°C. As a consequence films with carrier concentrations in the range 1016-1019 cm-3 can be prepared by adjusting temperature alone. By altering the background oxygen pressure (PD) we observe a change in the dominant defect - from tin interstitials (Sni) at low PD (< 50 mTorr) to VO at higher oxygen pressures with similar ranges of carrier concentrations observed. Finally we demonstrate the importance of controlling the composition target surface used for PLD by exposing a target to > 100,000 laser pulses. Here carrier concentrations > 1x1020 cm-3 are observed that are attributed to high concentrations of Sni which cannot be completely compensated for by modifying the growth parameters.

  3. Exploring and Controlling Intrinsic Defect Formation in SnO2 Thin Films

    KAUST Repository

    Porte, Yoann

    2015-12-15

    By investigating the influence of key growth variables on the measured structural and electrical properties of SnO2 prepared by Pulsed Laser Deposition (PLD) we demonstrate fine control of intrinsic n-type defect formation. Variation of growth temperatures shows oxygen vacancies (VO) as the dominant defect which can be compensated for by thermal oxidation at temperatures > 500°C. As a consequence films with carrier concentrations in the range 1016-1019 cm-3 can be prepared by adjusting temperature alone. By altering the background oxygen pressure (PD) we observe a change in the dominant defect - from tin interstitials (Sni) at low PD (< 50 mTorr) to VO at higher oxygen pressures with similar ranges of carrier concentrations observed. Finally we demonstrate the importance of controlling the composition target surface used for PLD by exposing a target to > 100,000 laser pulses. Here carrier concentrations > 1x1020 cm-3 are observed that are attributed to high concentrations of Sni which cannot be completely compensated for by modifying the growth parameters.

  4. Synthesis, characterization and formation mechanism of metastable phase VO2(A) nanorods

    International Nuclear Information System (INIS)

    Cheng, X.H.; Xu, H.F.; Wang, Z.Z.; Zhu, K.R.; Li, G.; Jin, Shaowei

    2013-01-01

    Graphical abstract: - Highlights: • Pure phases of VO 2 (B) and VO 2 (A) were prepared by a facile hydrothermal method. • Belt-like particles prepared at 180 °C was indexed as monoclinic VO 2 (B) phase. • Rod-like particles prepared at 230 °C was indexed as tetragonal VO 2 (A) phase. • VO 2 (A) nanorods resulted from VO 2 (B) nanobelts by assembly and crystal adjustment. - Abstract: Pure phase VO 2 (A) nanorods were synthesized via the reduction of V 2 O 5 by oxalic acid during the hydrothermal treatment. Two sets of samples were prepared by varying both system temperature and reaction time under a filling ratio of 0.40 for observing the formation and evolution of VO 2 (A) nanorods. Structures were characterized by X-ray diffraction, scanning and transmission electron microscopies, respectively. It was found that VO 2 (B) was firstly formed and then transformed into VO 2 (A) as the increasing system temperature or extending reaction time. An assembling and following crystal adjustment was proposed for explanation the formation process of VO 2 (A) from VO 2 (B). For VO 2 (A) nanorods, the phase transition temperature of 169.7 °C was higher than that of the VO 2 (A) bulk, it might be ascribed to the lower crystallinity or nonstoichiometry in VO 2 (A) nanorods. VO 2 nanostructures with controllable phases and properties should find their promising applications in a single VO 2 nanodevice

  5. Effects of three warm-up regimens of equal distance on VO2 kinetics during supramaximal exercise in Thoroughbred horses.

    Science.gov (United States)

    Mukai, K; Hiraga, A; Takahashi, T; Ohmura, H; Jones, J H

    2010-11-01

    Several studies have indicated that even low-intensity warm-up increases O(2) transport kinetics and that high-intensity warm-up may not be needed in horses. However, conventional warm-up exercise for Thoroughbred races is more intense than those utilised in previous studies of equine warm-up responses. To test the hypothesis that warm-up exercise at different intensities alters the kinetics and total contribution of aerobic power to total metabolic power in subsequent supramaximal (sprint) exercise in Thoroughbred horses. Nine well-trained Thoroughbreds ran until fatigue at 115% of maximal oxygen consumption (VO2max) 10 min after warming-up under each of 3 protocols of equal running distance: 400 s at 30% VO2max (LoWU), 200 s at 60% VO2max (MoWU) and 120 s at 100% VO2max (HiWU). Variables measured during exercise were rates of O(2) and CO(2) consumption/production (VO2,VO2), respiratory exchange ratio (RER), heart rate, blood lactate concentration and accumulation rate and blood gas variables. VO2 was significantly higher in HiWU than in LoWU at the onset of the sprint exercise and HR was significantly higher in HiWU than in LoWU throughout the sprint. Accumulation of blood lactate, RER, P(a)CO(2) and PvCO2 in the first 60 s were significantly lower in HiWU than in LoWU and MoWU. There were no significant differences in stroke volume, run time or arterial-mixed venous O(2) concentration. These results suggest HiWU accelerates kinetics and reduces reliance on net anaerobic power compared with LoWU at the onset of the subsequent sprint. © 2010 EVJ Ltd.

  6. Lattice relaxation and ferromagnetic character of (LaVO3)m/SrVO3 superlattices

    KAUST Repository

    Schuster, Cosima B.; Lü ders, Ulrike; Fré sard, Raymond; Schwingenschlö gl, Udo

    2013-01-01

    The experimental observation that vanadate superlattices (LaVO 3)m/SrVO3 show ferromagnetism up to room temperature (Lüders U. et al., Phys. Rev. B, 80 (2009) 241102(R)) is investigated by means of density functional theory, and the band structure for m = 5 and 6 is calculated. A buckling of the interface VO2 layers is found in both cases, but subtle differences in bond length lead to very different properties for even and odd values of m: in the even case, the two interface VO2 layers effectively decouple from the adjacent LaO layers due to a strong bond length enhancement. This results into a local inversion of the orbital occupancy and to the confinement of the charge carriers. In the odd case, the amplitude of the bond length variation is smaller, so that the charge carriers spill into the deeper-lying VO2 layers, and spin-polarised interfaces are obtained. © Copyright EPLA, 2013.

  7. Effect of vacancy loops on swelling of metals under irradiation

    International Nuclear Information System (INIS)

    Golubov, S.I.

    1981-01-01

    Subsequent analysis of vacancy loops formation in metals under irradiation is carried out and effect of vacancy loops on vacancy porosity is studied. Expression for quasistationary function of vacancy loops distribution according to sizes taking into consideration two mechanisms of their initiation-cascade and fluctuational ones - is obtained. It is shown that rate of vacancy absorption and interstitials by vacancy loops in quasiequilibrium state is similar and depends only on summary length of loops, for its calculations the self-coordinated procedure is formulated. For the rate of metal swelling under irradiation obtained is the expression taking into consideration the presence of vacancy loops [ru

  8. Precursor defect to the vacancy-dioxygen center in Si

    Science.gov (United States)

    Londos, C. A.; Sarlis, N.; Fytros, L. G.; Papastergiou, K.

    1996-03-01

    In a recent paper [Phys. Rev. B 50, 11 531 (1994)] we have tentatively attributed two new infrared bands at 914 cm -1 and 1000 cm-1, in neutron-irradiated Czochralski-grown silicon, to a [VO+Oi] structure that was considered to develop as an intermediate stage in the process of conversion of a VO center to a VO2 complex upon heat treatment. As a continuation of this work, we further investigate [VO+Oi] structure and the formation of intermediate defects. In addition, we present semiempirical calculations of the localized vibrational mode frequencies of the [VO+Oi] defect. The results are consistent with the experimental observations.

  9. Comparative study of optical and scintillation properties of YVO4, (Lu0.5Y0.5)VO4, and LuVO4 single crystals

    International Nuclear Information System (INIS)

    Fujimoto, Yutaka; Yanagida, Takayuki; Yokota, Yuui; Chani, Valery; Kochurikhin, Vladimir V.; Yoshikawa, Akira

    2011-01-01

    Optical and scintillation properties of YVO 4 , (Lu 0.5 Y 0.5 )VO 4 , and LuVO 4 single crystals grown by the Czochralski (CZ) method with RF heating system are compared. All vanadate crystals show high transmittance (∼80%) in the 400-900 nm wavelength range. In both photo- and radio-luminescence spectra, intense peak around 400-500 nm, which was ascribed to the transition from triplet state of VO 4 3- , was clearly observed. The main decay time component was about 38 μs (YVO 4 ), 18 μs ((Lu 0.5 Y 0.5 )VO 4 ), and 17 μs (LuVO 4 ) under 340 nm excitation. The scintillation light yields of YVO 4 , (Lu 0.5 Y 0.5 )VO 4 , and LuVO 4 crystals (obtained from the 137 Cs excited pulse height spectra) were evaluated to be about 11,200, 10,700, and 10,300 ph/MeV, respectively.

  10. First-principles studies of various crystallographic phases and neutral atomic vacancies in KNbO3 and KTaO3

    International Nuclear Information System (INIS)

    Shigemi, A.; Koyama, T.; Wada, T.

    2006-01-01

    We evaluated enthalpies of formation and formation energies of neutral vacancies in KNbO 3 and KTaO 3 using a plane-wave pseudopotential method within a density functional formalism. The KNbO 3 (R3mR) phase with the lowest symmetry was found to have the lowest enthalpy of formation. On the other hand, the various virtual KTaO 3 phases (P4mm, Bmm2 and R3mR) with the lower symmetry were found to be approximately equal to the enthalpy of formation of a cubic KTaO 3 phase at 0 K. For both KNbO 3 and KTaO 3 , the formation energy of a K vacancy was found to be the lowest under an oxidizing atmosphere and that of an O vacancy was found to be the lowest under a reducing atmosphere. The formation energy of a Nb/Ta vacancy was the highest under both oxygen-rich and -poor conditions. These results are in good agreement with the empirical rule that B site defects in perovskite-type oxide do not exist. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Vacancy ordering and superstructure formation in dry and hydrated strontium tantalate perovskites: A TEM perspective

    DEFF Research Database (Denmark)

    Ashok, Anuradha M.; Haavik, Camilla; Norby, Poul

    2014-01-01

    Crystal structures of Sr4(Sr2Ta2)O11 and Sr4(Sr1.92Ta2.08)O11.12, synthesized by solid state reaction technique in dry and hydrated state have been studied mainly using Transmission Electron Microscopy. Due to the lesser ability of X-rays to probe details in oxygen sublattice, the change in crystal...... and corresponding unit cells of all the perovskites based on the ordering of oxygen vacancies is deduced. Crystal unit cells based on the observations are proposed with ideal atomic coordinates. Finally an attempt is made to explain the water uptake behaviour of these perovskites based on the proposed crystal...

  12. Homogeneous double-layer amorphous Si-doped indium oxide thin-film transistors for control of turn-on voltage

    International Nuclear Information System (INIS)

    Kizu, Takio; Tsukagoshi, Kazuhito; Aikawa, Shinya; Nabatame, Toshihide; Fujiwara, Akihiko; Ito, Kazuhiro; Takahashi, Makoto

    2016-01-01

    We fabricated homogeneous double-layer amorphous Si-doped indium oxide (ISO) thin-film transistors (TFTs) with an insulating ISO cap layer on top of a semiconducting ISO bottom channel layer. The homogeneously stacked ISO TFT exhibited high mobility (19.6 cm"2/V s) and normally-off characteristics after annealing in air. It exhibited normally-off characteristics because the ISO insulator suppressed oxygen desorption, which suppressed the formation of oxygen vacancies (V_O) in the semiconducting ISO. Furthermore, we investigated the recovery of the double-layer ISO TFT, after a large negative shift in turn-on voltage caused by hydrogen annealing, by treating it with annealing in ozone. The recovery in turn-on voltage indicates that the dense V_O in the semiconducting ISO can be partially filled through the insulator ISO. Controlling molecule penetration in the homogeneous double layer is useful for adjusting the properties of TFTs in advanced oxide electronics.

  13. Dynamics of vacancies in two-dimensional Lennard-Jones crystals

    Science.gov (United States)

    Yao, Zhenwei; Olvera de La Cruz, Monica

    2015-03-01

    Vacancies represent an important class of crystallographic defects, and their behaviors can be strongly coupled with relevant material properties. We report the rich dynamics of vacancies in two-dimensional Lennard-Jones crystals in several thermodynamic states. Specifically, we numerically observe significantly faster diffusion of the 2-point vacancy with two missing particles in comparison with other types of vacancies; it opens the possibility of doping 2-point vacancies into atomic materials to enhance atomic migration. In addition, the resulting dislocations in the healing of a long vacancy suggest the intimate connection between vacancies and topological defects that may provide an extra dimension in the engineering of defects in extensive crystalline materials for desired properties. We thank the financial support from the U.S. Department of Commerce, National Institute of Standards and Technology, the Office of the Director of Defense Research and Engineering (DDR&E) and the Air Force Office of Scientific Research.

  14. Oxygen uptake and body composition after aquatic physical training in women with fibromyalgia: a randomized controlled trial.

    Science.gov (United States)

    Andrade, Carolina P; Zamunér, Antonio R; Forti, Meire; França, Thalita F; Tamburús, Nayara Y; Silva, Ester

    2017-10-01

    Aquatic physical training (APT) has been strongly recommended to improve symptoms in fibromyalgia syndrome (FMS). However, its effects on body composition and whether lean body mass (LBM) directly influences the aerobic functional capacity of this population are still not clear. To investigate whether APT can help improve body composition and increase the aerobic functional capacity in women with FMS, and whether oxygen uptake (VO2) related to LBM can better quantify the functional capacity of this population. Randomized controlled trial. The Federal University of São Carlos, São Paulo, Brazil. Fifty-four women with FMS were randomly assigned to trained group (TG, N.=27) or control group (CG, N.=27). All women underwent cardiopulmonary exercise test (CPET) to assess oxygen consumption at ventilatory anaerobic threshold (VAT) and at peak exercise, and also to assess body composition. The TG was submitted to APT program, held twice a week for 16 weeks. The exercise intensity was adapted throughout the sessions in order to keep heart rate and ratings of perceived exertion achieved at VAT. After APT, body composition was not significantly different between groups (TG and CG). In VAT only TG showed increased VO2 related to LBM, since in peak CPET, VO2 in absolute units, VO2 related to total body mass (TBM), VO2 related to LBM and power showed significant differences. Significant difference between VO2 related to TBM and VO2 related to baseline LBM and after 16 weeks of follow-up, both in VAT as in peak CPET in both groups. Significant difference between VO2 related to TBM and VO2 related to LBM at VAT and at peak CPET in both groups at baseline and after 16 weeks of follow-up was observed. APT with standardized intensities did not cause significant changes in body composition, but was effective in promoting increased VO2 at peak CPET in women with FMS. However, VO2 related to LBM more accurately reflected changes in aerobic functional capacity at VAT level after to

  15. Passivation of interstitial and vacancy mediated trap-states for efficient and stable triple-cation perovskite solar cells

    Science.gov (United States)

    Mahmud, Md Arafat; Elumalai, Naveen Kumar; Upama, Mushfika Baishakhi; Wang, Dian; Gonçales, Vinicius R.; Wright, Matthew; Xu, Cheng; Haque, Faiazul; Uddin, Ashraf

    2018-04-01

    The current work reports the concurrent passivation of interstitial and oxygen vacancy mediated defect states in low temperature processed ZnO electron transport layer (ETL) via Ultraviolet-Ozone (UVO) treatment for fabricating highly efficient (maximum efficiency: 16.70%), triple cation based MA0.57FA0.38Rb0.05PbI3 (MA: methyl ammonium, FA: formamidinium, Rb: rubidium) perovskite solar cell (PSC). Under UV exposure, ozone decomposes to free atomic oxygen and intercalates into the interstitial and oxygen vacancy induced defect sites in the ZnO lattice matrix, which contributes to suppressed trap-assisted recombination phenomena in perovskite device. UVO treatment also reduces the content of functional hydroxyl group on ZnO surface, that increases the inter-particle connectivity and grain size of perovskite film on UVO treated ZnO ETL. Owing to this, the perovskite film atop UVO treated ZnO film exhibits reduced micro-strain and dislocation density values, which contribute to the enhanced photovoltaic performance of PSC with modified ZnO ETL. The modified PSCs exhibit higher recombination resistance (RRec) ∼40% compared to pristine ZnO ETL based control devices. Adding to the merit, the UVO treated ZnO PSC also demonstrates superior device stability, retaining about 88% of its initial PCE in the course of a month-long, systematic degradation study.

  16. Oxygen measurements in thin ribbon silicon

    Energy Technology Data Exchange (ETDEWEB)

    Hyland, S L; Ast, D G; Baghdadi, A

    1987-03-01

    The oxygen content of thin silicon ribbons grown by the dendritic web technique was measured using a modification of the ASTM method based on Fourier transform infrared spectroscopy. Web silicon was found to have a high oxygen content, ranging from 13 to 19 ppma, calculated from the absorption peak associated with interstitial oxygen and using the new ASTM conversion coefficient. The oxygen concentration changed by about 10% along the growth direction of the ribbon. In some samples, a shoulder was detected on the absorption peak. A similar shoulder in Czochralski grown material has been variously interpreted in the literature as due to a complex of silicon, oxygen, and vacancies, or to a phase of SiO/sub 2/ developed along dislocations in the material. In the case of web silicon, it is not clear which is the correct interpretation.

  17. The Impact of Firefighter Personal Protective Equipment and Treadmill Protocol on Maximal Oxygen Uptake

    Science.gov (United States)

    Lee, Joo-Young; Bakri, Ilham; Kim, Jung-Hyun; Son, Su-Young; Tochihara, Yutaka

    2015-01-01

    This study investigated the effects of firefighter personal protective equipment (PPE) on the determination of maximal oxygen uptake (VO2max) while using two different treadmill protocols: a progressive incline protocol (PIP) and a progressive speed protocol (PSP), with three clothing conditions (Light-light clothing; Boots-PPE with rubber boots; Shoes-PPE with running shoes). Bruce protocol with Light was performed for a reference test. Results showed there was no difference in VO2max between Bruce Light, PIP Light, and PSP Light. However, VO2max was reduced in Boots and Shoes with shortened maximal performance time (7 and 6 min reduced for PIP Boots and Shoes, respectively; 11 and 9 min reduced for PSP Boots and Shoes, respectively), whereas the increasing rate of VO2 in Boots and Shoes during submaximal exercise was greater compared with Light. Wearing firefighter boots compared with wearing running shoes also significantly affected submaximal VO2 but not VO2max. These results suggest that firefighters’ maximal performance determined from a typical VO2max test without wearing PPE may overestimate the actual performance capability of firefighters wearing PPE. PMID:23668854

  18. On-line Monitoring of VoIP Quality Using IPFIX

    Directory of Open Access Journals (Sweden)

    Petr Matousek

    2014-01-01

    Full Text Available The main goal of VoIP services is to provide a reliable and high-quality voice transmission over packet networks. In order to prove the quality of VoIP transmission, several approaches were designed. In our approach, we are concerned about on-line monitoring of RTP and RTCP traffic. Based on these data, we are able to compute main VoIP quality metrics including jitter, delay, packet loss, and finally R-factor and MOS values. This technique of VoIP quality measuring can be directly incorporated into IPFIX monitoring framework where an IPFIX probe analyses RTP/RTCP packets, computes VoIP quality metrics, and adds these metrics into extended IPFIX flow records. Then, these extended data are stored in a central IPFIX monitoring system called collector where can be used for monitoring purposes. This paper presents a functional implementation of IPFIX plugin for VoIP quality measurement and compares the results with results obtained by other tools.

  19. Precursor defect to the vacancy-dioxygen center in Si

    International Nuclear Information System (INIS)

    Londos, C.A.; Sarlis, N.; Fytros, L.G.; Papastergiou, K.

    1996-01-01

    In a recent paper [Phys. Rev. B 50, 11531 (1994)] we have tentatively attributed two new infrared bands at 914 cm -1 and 1000 cm -1 , in neutron-irradiated Czochralski-grown silicon, to a [VO+O i ] structure that was considered to develop as an intermediate stage in the process of conversion of a VO center to a VO 2 complex upon heat treatment. As a continuation of this work, we further investigate [VO+O i ] structure and the formation of intermediate defects. In addition, we present semiempirical calculations of the localized vibrational mode frequencies of the [VO+O i ] defect. The results are consistent with the experimental observations. copyright 1996 The American Physical Society

  20. Self-regulated growth of LaVO3 thin films by hybrid molecular beam epitaxy

    International Nuclear Information System (INIS)

    Zhang, Hai-Tian; Engel-Herbert, Roman; Dedon, Liv R.; Martin, Lane W.

    2015-01-01

    LaVO 3 thin films were grown on SrTiO 3 (001) by hybrid molecular beam epitaxy. A volatile metalorganic precursor, vanadium oxytriisopropoxide (VTIP), and elemental La were co-supplied in the presence of a molecular oxygen flux. By keeping the La flux fixed and varying the VTIP flux, stoichiometric LaVO 3 films were obtained for a range of cation flux ratios, indicating the presence of a self-regulated growth window. Films grown under stoichiometric conditions were found to have the largest lattice parameter, which decreased monotonically with increasing amounts of excess La or V. Energy dispersive X-ray spectroscopy and Rutherford backscattering measurements were carried out to confirm film compositions. Stoichiometric growth of complex vanadate thin films independent of cation flux ratios expands upon the previously reported self-regulated growth of perovskite titanates using hybrid molecular beam epitaxy, thus demonstrating the general applicability of this growth approach to other complex oxide materials, where a precise control over film stoichiometry is demanded by the application

  1. Electrospinning synthesis of InVO{sub 4}/BiVO{sub 4} heterostructured nanobelts and their enhanced photocatalytic performance

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Zhendong; Lu, Qifang, E-mail: luqf0110@126.com; Guo, Enyan; Liu, Suwen [Qilu University of Technology, Shandong Provincial Key Laboratory of Processing and Testing Technology of Glass and Functional Ceramics, School of Material Science and Engineering (China)

    2016-08-15

    In the present work, one-dimensional InVO{sub 4}/BiVO{sub 4} heterostructured nanobelts with the width of about 800 nm have been successfully prepared by a simple electrospinning technique followed by the subsequent calcination process. The prepared products were characterized by thermogravimetry, fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–Vis absorbance spectroscopy, high-performance liquid chromatography, and photoluminescence spectroscopy. The obtained InVO{sub 4}/BiVO{sub 4} heterostructured nanobelts presented an admirable morphology and excellent photocatalytic properties for the degradation of methylene blue solution under visible-light irradiation.Graphical AbstractThe electrospun precursor samples (a and b) displayed a well-defined one-dimensional (1D) belt structure. After calcined at 550 °C for 2 h (c and d), the samples can retain well the 1D morphology. And an obvious porous structure can be found from the TEM images of the calcined samples (e and f).

  2. An attempt to specify thermal history in CZ silicon wafers and possibilities for its modification

    International Nuclear Information System (INIS)

    Kissinger, G.; Sattler, A.; Mueller, T.; Ammon, W. von

    2007-01-01

    The term thermal history of silicon wafers represents the whole variety of process parameters of crystal growth. The aim of this contribution is an attempt to specify thermal history by one parameter that is directly correlated to the bulk microdefect density. The parameter that reflects thermal history and correlates it with nucleation of oxide precipitates is the concentration of VO 2 complexes. The VO 2 concentration in silicon wafers is too low to be measured by FTIR but it can be obtained from the loss of interstitial oxygen during a standardized thermal treatment. Based on this, the vacancy concentration frozen during crystal cooling in the ingot can be calculated. RTA treatments above 1150 deg. C create a well defined level of the VO 2 concentration in silicon wafers. This means that a well controlled modification of the thermal history is possible. We also investigated the kinetics of reduction of the as-grown excess VO 2 concentration during RTA treatments at 950 deg. C and 1050 deg. C and the effectiveness of this attempt to totally delete the thermal history

  3. Vacancy clusters at nanoparticle surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J.; Moxom, J.; Somieski, B.; White, C.W. [Oak Ridge National Lab., TN (United States); Mills, A.P. Jr. [Bell Labs., Lucent Technologies, Murray Hill, NJ (United States); Suzuki, R.; Ishibashi, S. [Electrotechnical Lab., Tsukuba, Ibaraki (Japan); Ueda, A.; Henderson, D. [Physics Dept., Fisk Univ., Nashville, TN (United States)

    2001-07-01

    We detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v{sub 4}) are attached to the gold nanoparticle surfaces within the projected range (R{sub p}). (orig.)

  4. Vacancy clusters at nanoparticle surfaces

    International Nuclear Information System (INIS)

    Xu, J.; Moxom, J.; Somieski, B.; White, C.W.; Mills, A.P. Jr.; Suzuki, R.; Ishibashi, S.; Ueda, A.; Henderson, D.

    2001-01-01

    We detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v 4 ) are attached to the gold nanoparticle surfaces within the projected range (R p ). (orig.)

  5. Macroscopic results for a novel oxygenated silicon material

    International Nuclear Information System (INIS)

    Watts, S.J.; Da Via', C.; Karpenko, A.

    2002-01-01

    High-resistivity FZ silicon diodes have been processed in order to increase their oxygen dimer (O 2i ) concentration. Deep level transient spectroscopy measurements have been performed after proton irradiation showing that the formation of the VO centre is suppressed. The substrates had a starting resistivity of 2-4 kΩ cm, with an oxygen concentration of 10 15 and 10 17 cm -3 . Results for doping changes, leakage current and annealing behaviour after irradiation with 24 GeV/c protons are shown

  6. Prediction of VO[subscript 2]max in Children and Adolescents Using Exercise Testing and Physical Activity Questionnaire Data

    Science.gov (United States)

    Black, Nate E.; Vehrs, Pat R.; Fellingham, Gilbert W.; George, James D.; Hager, Ron

    2016-01-01

    Purpose: The purpose of this study was to evaluate the use of a treadmill walk-jog-run exercise test previously validated in adults and physical activity questionnaire data to estimate maximum oxygen consumption (VO[subscript 2]max) in boys (n = 62) and girls (n = 66) aged 12 to 17 years old. Methods: Data were collected from Physical Activity…

  7. Serum Tumor Necrosis Factor-alpha associates with Myocardial Oxygen Demand and Exercise Tolerance in Postmenopausal Women.

    Science.gov (United States)

    Carter, Stephen J; Bryan, David R; Neumeier, William H; Glasser, Stephen P; Hunter, Gary R

    2018-01-01

    The functional implications of serum tumor necrosis factor-alpha (TNF-α), a marker of oxidative stress, on hemodynamic parameters at rest and during physical exertion are unclear. The aims of this investigation were to examine the independent associations of TNF-α on myocardial oxygen demand at rest and during submaximal exercise, while also evaluating the association of TNF-α on exercise tolerance. Forty, postmenopausal women, provided blood samples and completed a modified-Balke protocol to measure maximal oxygen uptake (VO 2max ). Large artery compliance was measured by pulse contour analyses while rate-pressure product (RPP), an index of myocardial oxygen demand, was measured at rest and during two submaximal workloads (i.e., ≈55% and ≈75% VO 2max ). RPP was calculated by dividing the product of heart rate and systolic blood pressure (via auscultation) by 100. Exercise tolerance corresponded with the cessation of the graded exercise test. During higher-intensity exertion, ≈75% VO 2max , multiple linear regression revealed a positive association ( r = 0.43; p = 0.015) between TNF-α and RPP while adjusting for maximal heart rate, VO 2max , large artery compliance, and percent body fat. Path analyses revealed a significant indirect effect of large artery compliance on exercise tolerance through TNF-α, β = 0.13, CI [0.03, 0.35], indicating greater levels of TNF-α associated with poorer exercise tolerance. These data suggest TNF-α independently associates with myocardial oxygen demand during physical exertion, thus highlighting the utility of higher-intensity efforts to expose important phenomena not apparent at rest. TNF-α also appears to be indirectly associated with the link between large artery compliance and exercise tolerance.

  8. Defining and Measuring Job Vacancies in a Dynamic Perspective

    NARCIS (Netherlands)

    P.A. Donker van Heel (Peter)

    2015-01-01

    textabstractWhat is the best definition for job vacancies, what is the best method to measure job vacancies, and what further research is needed to gain a better insight into job vacancies in a dynamic perspective?

  9. Measurement of Diaphragmatic Blood Flow and Oxygen Consumption in the Dog by the Kety-Schmidt Technique

    Science.gov (United States)

    Rochester, Dudley F.

    1974-01-01

    To assess energy expenditure of the diaphragm directly, a method was devised for percutaneous catheterization of the left inferior phrenic vein in dogs. Necropsy studies, including retrograde injection of india ink and measurement of radioactivity in diaphragmatic muscle strips, suggested that the territory drained by the inferior phrenic vein was uniformly perfused, and that there were no major anastomoses between this bed and adjacent ones. Diaphragmatic blood flow (˙Q di) was calculated from the integrated diaphragmatic arteriovenous difference of 85Kr by the Kety-Schmidt technique. Diaphragmatic oxygen consumption (˙Vo2 di) was determined as the product of ˙Q di and the diaphragmatic arteriovenous oxygen content difference [(A-V)O2 di]. When lightly anesthetized dogs breathed quietly, ˙Q di was 22±SD 6 ml/min/100 g, (A-V)O2 di was 6.1±SD 2.5 ml/100 ml, and ˙VO2 di averaged 1.2±SD 0.3 ml/min/100 g. This represented 1.0±SD 0.2% of total body oxygen consumption. ˙VO2 di remained relatively constant during quiet breathing, whereas ˙Q di varied directly with cardiac output and reciprocally with (A-V)O2 di. The oxygen consumption of the noncontracting diaphragm was 60±SD 20% of the level measured during quiet breathing. The energy expended by the diaphragm to support simple hyperventilation was small. A 100% increase in minute ventilation, induced by inhalation of 5% CO2 in 21% or 14% O2, increased ˙Q di 13%, (A-V)O2 di 19%, and ˙VO2 di 40%. The diaphragm consumed 0.13±SD 0.09 ml O2 for each additional liter of ventilation. In four dogs, pneumonia appeared to increase ˙VO2 both by increasing minute ventilation and by increasing the energy cost per liter of ventilation. PMID:4825221

  10. Remarkable changes in interface O vacancy and metal-oxide bonds in amorphous indium-gallium-zinc-oxide thin-film transistors by long time annealing at 250 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chowdhury, Md Delwar Hossain; Um, Jae Gwang; Jang, Jin, E-mail: jjang@khu.ac.kr [Advanced Display Research Center and Department of Information Display, Kyung Hee University, Seoul 130-701 (Korea, Republic of)

    2014-12-08

    We have studied the effect of long time post-fabrication annealing on negative bias illumination stress (NBIS) of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film-transistors. Annealing for 100 h at 250 °C increased the field effect mobility from 14.7 cm{sup 2}/V s to 17.9 cm{sup 2}/V s and reduced the NBIS instability remarkably. Using X-ray photoelectron spectroscopy, the oxygen vacancy and OH were found to exist at the interfaces of a-IGZO with top and bottom SiO{sub 2}. Long time annealing helps to decrease the vacancy concentration and increase the metal-oxygen bonds at the interfaces; this leads to increase in the free carrier concentrations in a-IGZO and field-effect mobility. X-ray reflectivity measurement indicated the increment of a-IGZO film density of 5.63 g cm{sup −3} to 5.83 g cm{sup −3} (3.4% increase) by 100 h annealing at 250 °C. The increase in film density reveals the decrease of O vacancy concentration and reduction of weak metal-oxygen bonds in a-IGZO, which substantially helps to improve the NBIS stability.

  11. Impurities of oxygen in silicon

    International Nuclear Information System (INIS)

    Gomes, V.M.S.

    1985-01-01

    The electronic structure of oxygen complex defects in silicon, using molecular cluster model with saturation by watson sphere into the formalism of Xα multiple scattering method is studied. A systematic study of the simulation of perfect silicon crystal and an analysis of the increasing of atom number in the clusters are done to choose the suitable cluster for the calculations. The divacancy in three charge states (Si:V 2 + , Si:V 2 0 , Si:V 2 - ), of the oxygen pair (Si:O 2 ) and the oxygen-vacancy pair (Si:O.V) neighbours in the silicon lattice, is studied. Distortions for the symmetry were included in the Si:V 2 + and Si:O 2 systems. The behavior of defect levels related to the cluster size of Si:V 2 0 and Si:O 2 systems, the insulated oxygen impurity of silicon in interstitial position (Si:O i ), and the complexes involving four oxygen atoms are analysed. (M.C.K.) [pt

  12. Oxygen tracer studies of ferroelectric fatigue in Pb(Zr,Ti)O3 thin films

    International Nuclear Information System (INIS)

    Schloss, Lawrence F.; McIntyre, Paul C.; Hendrix, Bryan C.; Bilodeau, Steven M.; Roeder, Jeffrey F.; Gilbert, Stephen R.

    2002-01-01

    Long-range oxygen motion has been observed in Pt/Pb(Zr,Ti)O 3 /Ir thin-film structures after electrical fatigue cycling at room temperature. Through an exchange anneal, isotopic 18 O was incorporated as a tracer into bare Pb(Zr,Ti)O 3 (PZT) films, allowing secondary ion mass spectrometry measurements of the tracer profile evolution as a function of the number of polarization reversals. Observation of 18 O tracer redistribution during voltage cycling, which is presumably mediated by oxygen vacancy motion, was found to be strongly dependent upon the thermal history of the film. However, there was no strong correlation between the extent of 18 O tracer redistribution and the extent of polarization suppression induced by voltage cycling. Our results suggest that oxygen vacancy motion plays, at most, a secondary role in ferroelectric fatigue of PZT thin films

  13. Vacancy supersaturations produced by high-energy ion implantation

    International Nuclear Information System (INIS)

    Venezia, V.C.; Eaglesham, D.J.; Jacobson, D.C.; Gossmann, H.J.

    1998-01-01

    A new technique for detecting the vacancy clusters produced by high-energy ion implantation into silicon is proposed and tested. This technique takes advantage of the fact that metal impurities, such as Au, are gettered near one-half of the projected range (1/2 R p ) of MeV implants. The vacancy clustered region produced by a 2 MeV Si + implant into silicon has been labeled with Au diffused in from the front surface. The trapped Au was detected by Rutherford backscattering spectrometry (RBS) to profile the vacancy clusters. Cross section transmission electron microscopy (XTEM) analysis shows that the Au in the region of vacancy clusters is in the form of precipitates. By annealing MeV implanted samples prior to introduction of the Au, changes in the defect concentration within the vacancy clustered region were monitored as a function of annealing conditions

  14. Adjacent Fe-Vacancy Interactions as the Origin of Room Temperature Ferromagnetism in (In1 -xFex )2O3

    Science.gov (United States)

    Green, R. J.; Regier, T. Z.; Leedahl, B.; McLeod, J. A.; Xu, X. H.; Chang, G. S.; Kurmaev, E. Z.; Moewes, A.

    2015-10-01

    Dilute magnetic semiconductors (DMSs) show great promise for applications in spin-based electronics, but in most cases continue to elude explanations of their magnetic behavior. Here, we combine quantitative x-ray spectroscopy and Anderson impurity model calculations to study ferromagnetic Fe-substituted In2 O3 films, and we identify a subset of Fe atoms adjacent to oxygen vacancies in the crystal lattice which are responsible for the observed room temperature ferromagnetism. Using resonant inelastic x-ray scattering, we map out the near gap electronic structure and provide further support for this conclusion. Serving as a concrete verification of recent theoretical results and indirect experimental evidence, these results solidify the role of impurity-vacancy coupling in oxide-based DMSs.

  15. Ordered perovskites with cationic vacancies. 7. Structural investigations on Ba/sub 2/Zrsub(3/4)vacantsub(1/4)SbO/sub 6/

    Energy Technology Data Exchange (ETDEWEB)

    Treiber, U; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

    1980-11-01

    The ochre coloured Ba/sub 2/Zrsub(3/4)vacantsub(1/4)SbO/sub 6/ belongs to the group of oxygen perovskites with an ordered distribution of the vacancies. It crystallizes tetragonal (a = 11.68/sub 5/ A; c = 16.60/sub 6/ A) with 16 formula units in the cell: Ba/sub 32/Zr/sub 12/vacant/sub 4/Sb/sub 16/O/sub 96/. For the space group P 4/mmm intensity calculations on powder data gave a refined, intensity related R' value of 4.8%. In the structure the Zr and Ba atoms are ordered (1:1 order); the four cationic vacancies are located in a face centered arrangement in the zirconium sublattice. The Ba atoms are displaced by approximately 0.20 A in direction of the neighbouring vacancy, while the other cations maintain their ideal positions.

  16. Oxygen consumption rates in hovering hummingbirds reflect substrate-dependent differences in P/O ratios: carbohydrate as a 'premium fuel'.

    Science.gov (United States)

    Welch, Kenneth C; Altshuler, Douglas L; Suarez, Raul K

    2007-06-01

    The stoichiometric relationship of ATP production to oxygen consumption, i.e. the P/O ratio, varies depending on the nature of the metabolic substrate used. The latest estimates reveal a P/O ratio approximately 15% higher when glucose is oxidized compared with fatty acid oxidation. Because the energy required to produce aerodynamic lift for hovering is independent of the metabolic fuel oxidized, we hypothesized that the rate of oxygen consumption, VO2, should decline as the respiratory quotient, RQ (VCO2/VO2), increases from 0.71 to 1.0 as hummingbirds transition from a fasted to a fed state. Here, we show that hovering VO2 values in rufous (Selasphorus rufus) and Anna's hummingbirds (Calypte anna) are significantly greater when fats are metabolized (RQ=0.71) than when carbohydrates are used (RQ=1.0). Because hummingbirds gained mass during our experiments, making mass a confounding variable, we estimated VO2 per unit mechanical power output. Expressed in this way, the difference in VO2 when hummingbirds display an RQ=0.71 (fasted) and an RQ=1.0 (fed) is between 16 and 18%, depending on whether zero or perfect elastic energy storage is assumed. These values closely match theoretical expectations, indicating that a combination of mechanical power estimates and ;indirect calorimetry', i.e. the measurement of rates of gas exchange, enables precise estimates of ATP turnover and metabolic flux rates in vivo. The requirement for less oxygen when oxidizing carbohydrate suggests that carbohydrate oxidation may facilitate hovering flight in hummingbirds at high altitude.

  17. Influence of oxygen flow rate on metal-insulator transition of vanadium oxide thin films grown by RF magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Xu; Liu, Xinkun; Li, Haizhu; Huang, Mingju [Henan University, Key Lab of Informational Opto-Electronical Materials and Apparatus, School of Physics and Electronics, Kaifeng (China); Zhang, Angran [South China Normal University, Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, Guangzhou (China)

    2017-03-15

    High-quality vanadium oxide (VO{sub 2}) films have been fabricated on Si (111) substrates by radio frequency (RF) magnetron sputtering deposition method. The sheet resistance of VO{sub 2} has a significant change (close to 5 orders of magnitude) in the process of the metal-insulator phase transition (MIT). The field emission-scanning electron microscope (FE-SEM) results show the grain size of VO{sub 2} thin films is larger with the increase of oxygen flow. The X-ray diffraction (XRD) results indicate the thin films fabricated at different oxygen flow rates grow along the (011) crystalline orientation. As the oxygen flow rate increases from 3 sccm to 6 sccm, the phase transition temperature of the films reduces from 341 to 320 K, the width of the thermal hysteresis loop decreases from 32 to 9 K. The thin films fabricated in the condition of 5 sccm have a high temperature coefficient of resistance (TCR) -3.455%/K with a small resistivity of 2.795 ρ/Ω cm. (orig.)

  18. Anti-biofouling function of amorphous nano-Ta2O5 coating for VO2-based intelligent windows

    Science.gov (United States)

    Li, Jinhua; Guo, Geyong; Wang, Jiaxing; Zhou, Huaijuan; Shen, Hao; Yeung, Kelvin W. K.

    2017-04-01

    From environmental and health perspectives, the acquisition of a surface anti-biofouling property holds important significance for the usability of VO2 intelligent windows. Herein, we firstly deposited amorphous Ta2O5 nanoparticles on VO2 film by the magnetron sputtering method. It was found that the amorphous nano-Ta2O5 coating possessed a favorable anti-biofouling capability against Pseudomonas aeruginosa as an environmental microorganism model, behind which lay the mechanism that the amorphous nano-Ta2O5 could interrupt the microbial membrane electron transport chain and significantly elevate the intracellular reactive oxygen species (ROS) level. A plausible relationship was established between the anti-biofouling activity and physicochemical nature of amorphous Ta2O5 nanoparticles from the perspective of defect chemistry. ROS-induced oxidative damage gave rise to microbial viability loss. In addition, the amorphous nano-Ta2O5 coating can endow VO2 with favorable cytocompatibility with human skin fibroblasts. This study may provide new insights into understanding the anti-biofouling and antimicrobial actions of amorphous transition metal oxide nanoparticles, which is conducive to expanding their potential applications in environmental fields.

  19. 24 CFR 983.352 - Vacancy payment.

    Science.gov (United States)

    2010-04-01

    ... PROJECT-BASED VOUCHER (PBV) PROGRAM Payment to Owner § 983.352 Vacancy payment. (a) Payment for move-out month. If an assisted family moves out of the unit, the owner may keep the housing assistance payment... 24 Housing and Urban Development 4 2010-04-01 2010-04-01 false Vacancy payment. 983.352 Section...

  20. Myosin heavy chain composition in the vastus lateralis muscle in relation to oxygen uptake and heart rate during cycling in humans.

    Science.gov (United States)

    Majerczak, J; Nieckarz, Z; Karasinski, J; Zoladz, J A

    2014-04-01

    In this study we examined the relationship between fast myosin heavy chain (MyHC2) content in the vastus lateralis and the rate of oxygen uptake (VO2) and heart rate (HR) increase during an incremental exercise in 38, young, healthy men. Prior to the exercise test, muscle biopsies were taken in order to evaluate the MyHC composition. It was found that during cycling performed below the lactate threshold (LT), a positive relationship between MyHC2 and the intercept of the oxygen uptake and power output (VO2-PO) relationship existed (r=0.49, P=0.002), despite no correlation between MyHC2 and the slope value of the VO2-PO relationship (r= -0.18, P=0.29). During cycling performed above the LT, MyHC2 correlated positively with the magnitude of the nonlinearity in the VO2-PO relationship; i.e. with the accumulated VO2'excess' (r=0.44, P=0.006) and peak VO2'excess' (r=0.44, P=0.006), as well as with the slope of the HR-PO relationship (r=0.49, P=0.002). We have concluded that a greater MyHC2 content in the vastus lateralis is accompanied by a higher oxygen cost of cycling during exercise performed below the LT. This seems to be related to the higher energy cost of the non-cross-bridge activities in the muscles possessing a greater proportion of MyHC2 content. In the case of heavy-intensity exercise, a higher MyHC2 content in the vastus lateralis is accompanied by greater non-linearity in the VO2-PO relationship, as well as a steeper increase in HR in the function of an increase of PO. This relationship can be explained by greater disturbances in metabolic stability in type II muscle fibres during exercise, resulting in a decrease of muscle mechanical efficiency and greater increase of heart rate at a given power output. Therefore, MyHC composition has an impact on the oxygen cost of cycling both below and above the LT.

  1. Vacancy dynamic in Ni-Mn-Ga ferromagnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Merida, D., E-mail: david.merida@ehu.es [Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); Elektrizitate eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); García, J. A. [Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); BC Materials (Basque Centre for Materials, Application and Nanostructures), 48040 Leioa (Spain); Sánchez-Alarcos, V.; Pérez-Landazábal, J. I.; Recarte, V. [Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadia, 31006 Pamplona (Spain); Plazaola, F. [Elektrizitate eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain)

    2014-06-09

    Vacancies control any atomic ordering process and consequently most of the order-dependent properties of the martensitic transformation in ferromagnetic shape memory alloys. Positron annihilation spectroscopy demonstrates to be a powerful technique to study vacancies in NiMnGa alloys quenched from different temperatures and subjected to post-quench isothermal annealing treatments. Considering an effective vacancy type the temperature dependence of the vacancy concentration has been evaluated. Samples quenched from 1173 K show a vacancy concentration of 1100 ± 200 ppm. The vacancy migration and formation energies have been estimated to be 0.55 ± 0.05 eV and 0.90 ± 0.07 eV, respectively.

  2. Hydrothermal synthesis and electrochemical characterization of VO2 (B) with controlled crystal structures

    International Nuclear Information System (INIS)

    Jiang Wentao; Ni Juan; Yu Ke; Zhu Ziqiang

    2011-01-01

    Three different VO 2 (B) nanostructures, including urchin-like VO 2 (B), VO 2 (B) honeycombs and VO 2 (B) nanorods have been successfully fabricated through hydrothermal process by adjusting the concentrations of the oxalic acid. The microstructure and morphology of the VO 2 nanostructures were evaluated by using X-ray diffraction and scanning and transmission electron microscopies. Electrochemical properties measurements of urchin-like VO 2 (B) and VO 2 (B) honeycombs showed excellent cycling performance, especially the urchin-like VO 2 (B) exhibited higher discharge capacity and better capacity retention.

  3. Graphene/VO2 hybrid material for high performance electrochemical capacitor

    International Nuclear Information System (INIS)

    Deng, Lingjuan; Zhang, Gaini; Kang, Liping; Lei, Zhibin; Liu, Chunling; Liu, Zong-Huai

    2013-01-01

    Graphical abstract: Graphene/VO 2 hybrid materials are prepared by one-step simultaneous hydrothermal reduction technology. The prepared graphene (1.0)/VO 2 hybrid material shows a specific capacitances of 225 F g −1 in 0.5 mol L −1 K 2 SO 4 solution. Furthermore, an asymmetric electrochemical capacitor with graphene (1.0)/VO 2 as a positive electrode and graphene as a negative electrode is assembled, and it can work in a cell voltage of 1.7 V and show excellent capacitive property. - Highlights: • Graphene/VO 2 hybrid material has been prepared by one-step hydrothermal reduction. • Graphene/VO 2 hybrid material exhibits high specific capacitance. • An asymmetric capacitor working at 1.7 V in aqueous solution is assembled based on graphene/VO 2 electrode. • The asymmetric capacitor exhibits high energy density. - Abstract: Vanadium oxides have attracted significant attention for electrochemical capacitor because of their extensive multifunctional properties. In the present work, graphene/VO 2 (RG/VO 2 ) hybrid materials with different RG amounts are prepared in a mixture of ammonium vanadate, formic acid and graphite oxide (GO) nanosheets by one-step simultaneous hydrothermal reduction technology. The hydrothermal treatment makes the reduction of GO into RG and the formation of VO 2 particles with starfruit morphology. The starfruit-like VO 2 particles are uniformly embedded in the hole constructed by RG nanosheets, which makes the electrode–electrolyte contact better. A high specific capacitance of 225 F g −1 has been achieved for RG(1.0)/VO 2 electrode with RG content of 26 wt% in 0.5 mol L −1 K 2 SO 4 electrolyte. An asymmetrical electrochemical capacitor is assembled by using RG(1.0)/VO 2 as positive electrode and RG as negative electrode, and it can be reversibly charged–discharged at a cell voltage of 1.7 V in 0.5 mol L −1 K 2 SO 4 electrolyte. The asymmetrical capacitor can deliver an energy density of 22.8 Wh kg −1 at a power density

  4. Integrating a Semitransparent, Fullerene-Free Organic Solar Cell in Tandem with a BiVO4 Photoanode for Unassisted Solar Water Splitting.

    Science.gov (United States)

    Peng, Yuelin; Govindaraju, Gokul V; Lee, Dong Ki; Choi, Kyoung-Shin; Andrew, Trisha L

    2017-07-12

    We report an unassisted solar water splitting system powered by a diketopyrrolopyrrole (DPP)-containing semitransparent organic solar cell. Two major merits of this fullerene-free solar cell enable its integration with a BiVO 4 photoanode. First is the high open circuit voltage and high fill factor displayed by this single junction solar cell, which yields sufficient power to effect water splitting when serially connected to an appropriate electrode/catalyst. Second, the wavelength-resolved photoaction spectrum of the DPP-based solar cell has minimal overlap with that of the BiVO 4 photoanode, thus ensuring that light collection across these two components can be optimized. The latter feature enables a new water splitting device configuration wherein the solar cell is placed first in the path of incident light, before the BiVO 4 photoanode, although BiVO 4 has a wider bandgap. This configuration is accessed by replacing the reflective top electrode of the standard DPP-based solar cell with a thin metal film and an antireflection layer, thus rendering the solar cell semitransparent. In this configuration, incident light does not travel through the aqueous electrolyte to reach the solar cell or photoanode, and therefore, photon losses due to the scattering of water are reduced. Moreover, this new configuration allows the BiVO 4 photoanode to be back-illuminated, i.e., through the BiVO 4 /back contact interface, which leads to higher photocurrents compared to front illumination. The combination of a semitransparent single-junction solar cell and a BiVO 4 photoanode coated with oxygen evolution catalysts in a new device configuration yielded an unassisted solar water splitting system with a solar-to-hydrogen conversion efficiency of 2.2% in water.

  5. Oxygen cost and physiological responses of recreational badminton match play.

    Science.gov (United States)

    Deka, Pallav; Berg, Kris; Harder, Jeanette; Batelaan, Herman; McGRATH, Melanie

    2017-06-01

    Badminton, as an Olympic sport, is popular worldwide. However, the benefits of recreational badminton match play are not well known. The purpose of the study was to determine the oxygen cost of recreational badminton match play. Heart rate (HR), blood lactate (BL), rating of perceived exertion (RPE), step count and energy expenditure were also assessed. Fourteen male recreational badminton players aged 35.9±6.62 years participated in test sessions to assess oxygen uptake (VO2) and the related physiological responses of match play. During the match play sessions, participants played singles badminton matches for 30 min while wearing a portable metabolic system. VO2 and HR were continuously recorded while blood lactate and RPE were determined following warm-up, at 15 minutes and 30 minutes of match play. Step count was recorded at 15 minutes and 30 minutes of play. VO2 over 30 minutes was 34.4±5.8 mL/kg/min which was 76.1% of maximal oxygen uptake. Across three 10-minute periods of play, VO2 was not significantly different while HR was higher in the third 10-minute period than the first and second 10-minute periods (P=0.001). Mean HR over 30 minutes was 167.9±9.4 bpm. BL was significantly higher at 15 and 30 minutes than following warm-up while RPE of 17.57±1.91 after 30 minutes was significantly higher (P=0.009) than RPE of 15.79±1.63 at 15 minutes. Step count did not vary between the two 15-minute periods of play with a total of 2404±360 steps while energy expenditure over 30 minutes of play was 391.7±66 kcal. Recreational badminton match play can be categorized as vigorous intensity suggesting that it can be a viable means of achieving recommended physical activity and improving aerobic fitness.

  6. Contribution to the study of vacancies in silver and uranium (1962); Contribution a l'etude des lacunes dans l'argent et l'uranium (1962)

    Energy Technology Data Exchange (ETDEWEB)

    Quere, Y [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1961-12-15

    In metals, high temperature vacancies can be retained by quenching. Results are given for the quenching of uranium (in liquid helium) and of silver (in liquid nitrogen). In this last case the energy of formation (1.06 eV) and the energy of mobility (0.86 eV) of the vacancies have been measured as well as the energy of mobility of the divacancies (0.58 eV). If the quenching is slow, it is shown that it is possible to trap the vacancies on the impurities of the metal. This leads to increases in the electrical resistivity observed by annealing after quenching, the vacancies being released before disappearing into sinks. The vacancy-impurity binding energy (the impurity being probably oxygen which is present in the silver used at a concentration of 20 ppm. atom.) can thus be estimated to be 0.4 eV. (author) [French] Dans un metal, les lacunes de haute temperature peuvent etre retenues par trempe. On presente des experiences de trempe d'uranium (dans l'helium liquide) et d'argent (dans l'azote liquide). Dans ce dernier cas, on mesure l'energie de formation (1,06 eV) et l'energie de mobilite (0,86 eV) des lacunes ainsi que l'energie de mobilite des bilacunes (0,58 eV). Si la trempe est lente, on montre que l'on peut pieger des lacunes sur les impuretes du metal. On interprete de cette facon des augmentations de resistivite electrique observees par recuit apres trempe, les lacunes se depiegeant avant de disparaitre dans des puits. L'energie de liaison lacune-impurete (l'impurete etant probablement l'oxygene dont l'argent utilise contient 20 ppm. atom.) peut alors etre evalue 0,4 eV. (auteur)

  7. Mobility and stability of large vacancy and vacancy-copper clusters in iron: An atomistic kinetic Monte Carlo study

    Energy Technology Data Exchange (ETDEWEB)

    Castin, N., E-mail: ncastin@sckcen.be [Studiecentrum voor Kernenergie - Centre d' Etudes de l' energie Nucleaire (SCK-CEN), Nuclear Materials Science Institute, Unit Structural Materials Modelling and Microstructure-Boeretang 200, B2400 Mol (Belgium); Pascuet, M.I., E-mail: pascuet@cnea.gov.ar [Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Av. Rivadavia 1917, C1033AAJ Buenos Aires (Argentina); Malerba, L. [Studiecentrum voor Kernenergie - Centre d' Etudes de l' energie Nucleaire (SCK-CEN), Nuclear Materials Science Institute, Unit Structural Materials Modelling and Microstructure-Boeretang 200, B2400 Mol (Belgium)

    2012-10-15

    The formation of Cu-rich precipitates under irradiation is a major cause for changes in the mechanical response to load of reactor pressure vessel steels. In previous works, it has been shown that the mechanism under which precipitation occurs is governed by diffusion of vacancy-copper (VCu) complexes, also in the absence of irradiation. Coarse-grained computer models (such as object kinetic Monte Carlo) aimed at simulating irradiation processes in model alloys or steels should therefore explicitly include the mobility of Cu precipitates, as a consequence of vacancy hops at their surface. For this purpose, in this work we calculate diffusion coefficients and lifetimes for a large variety of VCu complexes. We use an innovative atomistic model, where vacancy migration energies are calculated with little approximations, taking into account all effects of static relaxation and long-range chemical interaction as predicted by an interatomic potential. Our results show that, contrary to what intuition might suggest, saturation in vacancies tend to slow down the transport of Cu atoms.

  8. Using VoIP to compete.

    Science.gov (United States)

    Werbach, Kevin

    2005-09-01

    Internet telephony, or VoIP, is rapidly replacing the conventional kind. This year, for the first time, U.S. companies bought more new Internet-phone connections than standard lines. The major driver behind this change is cost. But VoIP isn't just a new technology for making old-fashioned calls cheaper, says consultant Kevin Werbach. It is fundamentally changing how companies use voice communications. What makes VoIP so powerful is that it turns voice into digital data packets that can be stored, copied, combined with other data, and distributed to virtually any device that connects to the Internet. And it makes it simple to provide all the functionality of a corporate phone-call features, directories, security-to anyone anywhere there's broadband access. That fosters new kinds of businesses such as virtual call centers, where widely dispersed agents work at all hours from their homes. The most successful early adopters, says Werbach, will focus more on achieving business objectives than on saving money. They will also consider how to push VoIP capabilities out to the extended organization, making use of everyone as a resource. Deployment may be incremental, but companies should be thinking about where VoIP could take them. Executives should ask what they could do if, on demand, they could bring all their employees, customers, suppliers, and partners together in a virtual room, with shared access to every modern communications and computing channel. They should take a fresh look at their business processes to find points at which richer and more customizable communications could eliminate bottlenecks and enhance quality. The important dividing line won't be between those who deploy Vol P and those who don't, or even between early adopters and laggards. It will be between those who see Vol P as just a new way to do the same old things and those who use itto rethink their entire businesses.

  9. Electrocatalytic activity of cobalt phosphide-modified graphite felt toward VO2+/VO2+ redox reaction

    Science.gov (United States)

    Ge, Zhijun; Wang, Ling; He, Zhangxing; Li, Yuehua; Jiang, Yingqiao; Meng, Wei; Dai, Lei

    2018-04-01

    A novel strategy for improving the electro-catalytic properties of graphite felt (GF) electrode in vanadium redox flow battery (VRFB) is designed by depositing cobalt phosphide (CoP) onto GF surface. The CoP powder is synthesized by direct carbonization of Co-based zeolitic imidazolate framework (ZIF-67) followed by phosphidation. Cyclic voltammetry results confirm that the CoP-modified graphite felt (GF-CoP) electrode has excellent reversibility and electro-catalytic activity to the VO2+/VO2+ cathodic reaction compared with the pristine GF electrode. The cell using GF-CoP electrode shows apparently higher discharge capacity over that based on GF electrode. The cell using GF-CoP electrode has the capacity of 67.2 mA h at 100 mA cm-2, 32.7 mA h larger than that using GF electrode. Compared with cell using GF electrode, the voltage efficiency of the cell based on GF-CoP electrode increases by 5.9% and energy efficiency by 5.4% at a current density of 100 mA cm-2. The cell using GF-CoP electrode can reach 94.31% capacity retention after 50 cycles at a current density of 30 mA cm-2. The results show that the CoP can effectively promote the VO2+/VO2+ redox reaction, implying that metal phosphides are a new kind of potential catalytic materials for VRFB.

  10. The relationship between heart rate and rate of oxygen consumption in Galapagos marine iguanas (Amblyrhynchus cristatus) at two different temperatures.

    Science.gov (United States)

    Butler, Patrick J; Frappell, Peter B; Wang, Tobias; Wikelski, Martin

    2002-07-01

    To enable the use of heart rate (fH) for estimating field metabolic rate (FMR) in free-ranging Galapagos marine iguanas Amblyrhynchus cristatus, we determined the relationships between fH and mass-specific rate of oxygen consumption (sVO2) in seven iguanas before and during exercise on a treadmill and during the post-exercise period. The experiments were conducted at 27 and 35 degrees C, which are the temperatures that represent the lowest and highest average body temperatures of these animals in the field during summer. There were linear and significant relationships between fH and sVO2 at both temperatures (r(2)=0.86 and 0.91 at 27 degrees C and 36 degrees C, respectively). The slopes of the two regression lines did not differ, but there were significant differences in their intercepts. Thus, while heart rate can be used to predict FMR, the effects of temperature on the intercept of the regression must be taken into account when converting fH to sVO2. On the basis of our data, this can be achieved by applying the following formula: sVO2=0.0113fH-0.2983Q(10)((T(b)-27)/10). The increase in sVO2 with elevated body temperature results from an increase in fH, with no significant change in mass-specific oxygen pulse (sO(2) pulse; cardiac stroke volume times the difference in oxygen content between arterial and mixed venous blood). However, during exercise at both temperatures, increases in fH are insufficient to provide all of the additional O(2) required and there are also significant increases in the sO(2) pulses. This creates the situation whereby the same fH at the two temperatures can represent different values of sVO2.

  11. Vacancies and defect levels in III–V semiconductors

    KAUST Repository

    Tahini, H. A.

    2013-08-13

    Using electronic structure calculations, we systematically investigate the formation of vacancies in III-V semiconductors (III = Al, Ga, and In and V = P, As, and Sb), for a range of charges ( −3≤q≤3 ) as a function of the Fermi level and under different growth conditions. The formation energies were corrected using the scheme due to Freysoldt et al. [Phys. Rev. Lett. 102, 016402 (2009)] to account for finite size effects. Vacancy formation energies were found to decrease as the size of the group V atom increased. This trend was maintained for Al-V, Ga-V, and In-V compounds. The negative-U effect was only observed for the arsenic vacancy in GaAs, which makes a charge state transition from +1 to –1. It is also found that even under group III rich conditions, group III vacancies dominate in AlSb and GaSb. For InSb, group V vacancies are favoured even under group V rich conditions.

  12. Vacancies and defect levels in III–V semiconductors

    KAUST Repository

    Tahini, H. A.; Chroneos, Alexander; Grimes, R. W.; Murphy, S. T.; Schwingenschlö gl, Udo

    2013-01-01

    Using electronic structure calculations, we systematically investigate the formation of vacancies in III-V semiconductors (III = Al, Ga, and In and V = P, As, and Sb), for a range of charges ( −3≤q≤3 ) as a function of the Fermi level and under different growth conditions. The formation energies were corrected using the scheme due to Freysoldt et al. [Phys. Rev. Lett. 102, 016402 (2009)] to account for finite size effects. Vacancy formation energies were found to decrease as the size of the group V atom increased. This trend was maintained for Al-V, Ga-V, and In-V compounds. The negative-U effect was only observed for the arsenic vacancy in GaAs, which makes a charge state transition from +1 to –1. It is also found that even under group III rich conditions, group III vacancies dominate in AlSb and GaSb. For InSb, group V vacancies are favoured even under group V rich conditions.

  13. Synthesis of sub-10 nm VO2 nanoparticles films with plasma-treated glass slides by aqueous sol–gel method

    International Nuclear Information System (INIS)

    Lan, Shi-Di; Cheng, Chih-Chia; Huang, Chi-Hsien; Chen, Jem-Kun

    2015-01-01

    Highlights: • Sub-10 nm VO 2 nanoparticles (VNPs) are synthesized on a plasma-treated glass. • Glass slides generate negative charges sites after plasma treatment to attract VO 2 + . • Doping tungsten with 1 wt% in VNPs did not change particle size significantly. • The particle size of VNP can be tuned by the density of negative charge sites. • Sub-10 nm structured VO 2 particle films exhibited high visible transmittance. - Abstract: This paper describes an aqueous sol–gel synthesis of thermochromic thin films consisted of vanadium dioxide nanoparticles (VNPs) on glass slides. The glass slides were treated by argon/oxygen plasma to generate dispersedly negative charge sites on the surface to attract VO 2 + from a sol–gel solution. After heat treatment in a low-pressure carbon monoxide/carbon dioxide (CO/CO 2 ) atmosphere, the VNPs could be generated in sub-10 nm of particle size on the surface. Various levels of doping were achieved by adding small quantities of a water-soluble tungsten compound to the sol; however, the particle size increased slightly with the tungsten doping levels. The change in electrical conductivity with temperature for VNP films were measured and compared to VO 2 crystalline films. VNP films exhibited the lower transition temperature of the semiconductor to metal phase change; at a doping level of 4 wt% the transition temperature was measured at 32.2 ± 1.2 and 24.1 ± 1.2 °C for the VO 2 and VNP films, respectively. The VNP films showed excellent visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal–insulator phase transition (MIT). The current method is a landmark in the development of nanostructured material toward applications in energy-saving smart windows.

  14. Ordered array of CoPc-vacancies filled with single-molecule rotors

    Science.gov (United States)

    Xie, Zheng-Bo; Wang, Ya-Li; Tao, Min-Long; Sun, Kai; Tu, Yu-Bing; Yuan, Hong-Kuan; Wang, Jun-Zhong

    2018-05-01

    We report the highly ordered array of CoPc-vacancies and the single-molecule rotors inside the vacancies. When CoPc molecules are deposited on Cd(0001) at low-temperature, three types of molecular vacancies appeared randomly in the CoPc monolayer. Annealing the sample to higher temperature leads to the spontaneous phase separation and self-organized arrangement of the vacancies. Highly ordered arrays of two-molecule vacancies and single-molecule vacancies have been obtained. In particular, there is a rotating CoPc molecule inside each single-molecule vacancy, which constitutes the array of single-molecule rotors. These results provide a new routine to fabricate the nano-machines on a large scale.

  15. Estimativa das contribuições dos sistemas anaeróbio lático e alático durante exercícios de cargas constantes em intensidades abaixo do VO2max Estimation of contributions of the anaerobic lactic and alactic systems during constant-load exercises at intensities below the VO2max

    Directory of Open Access Journals (Sweden)

    Marcos David Silva-Cavalcante

    2013-01-01

    Full Text Available O objetivo do estudo foi estimar as contribuições do metabolismo anaeróbio lático (MAL e alático (MAA em intensidades abaixo do consumo máximo de oxigênio (VO2max. Dez homens (23 ± 4 anos, 176,4 ± 6,8 cm, 72,4 ± 8,2 kg, 12,0 ± 4,5 % de gordura corporal realizaram um teste progressivo até a exaustão voluntária para identificação do VO2max, da potência correspondente ao VO2max (WVO2max e do segundo limiar ventilatório (LV2. Na segunda e na terceira visita foram realizados seis testes de cargas constantes (três testes por sessão com intensidades abaixo do VO2max. Houve uma predominância do MAL sobre o MAA durante os exercícios submáximos a partir da intensidade correspondente ao LV2, sendo significativamente maior em 90% VO2max (p The purpose this study was that estimated contributions of the anaerobic lactic (MAL and alactic (MAA metabolism during constant load exercises at intensities below the maximal oxygen capacity uptake (VO2max. Ten males (23 ± 4 years, 176.4 ± 6.8 cm, 72.4 ± 8.2 kg, 12.0 ± 4.5 % of fat body performed in the first visit a progressive test until exhaustion to identification of VO2max, power output corresponding to the VO2max (WVO2max and second ventilatory threshold (LV2. On the second and third visit, the participants performed six constant workload tests (3 per session with intensities below VO2max. There was a predominance of MAL about MAA during the exercises sub-maximal from intensity corresponding to the LV2, being significantly higher at 90% VO2max (p < 0.05. Thus, these results may help coaches to implement training loads appropriate to their athletes, according to the metabolic demand of the competition.

  16. Oxygen consumption during exercise in a heated pool.

    Science.gov (United States)

    Kirby, R L; Sacamano, J T; Balch, D E; Kriellaars, D J

    1984-01-01

    The heated hydrotherapy pool is a common exercise site for patients with painful musculoskeletal conditions. Oxygen consumption of swimming is 87 to 89% of maximum in postmyocardial infarction patients according to one recent investigation. We studied 13 able-bodied subjects to test the hypothesis that enough energy could be expended during various forms of hydrotherapy to produce both an aerobic training effect and a risk to patients with coronary artery disease. Oxygen consumption (VO2) was measured in six settings: resting supine; resting seated shoulder deep in the pool (36C); walking at comfortable speed in chest-deep water; running at the fastest speed possible in chest-deep water; using hand paddles; and running in place at shoulder depth. The mean VO2 expressed in ml/kg/min (and metabolic equivalents) were 4.91 (1.00), 4.93 (1.02), 9.34 (2.01), 27.79 (6.23), 18.25 (4.30) and 29.11 (7.09) respectively, suggesting that the more vigorous exercises stress aerobic capacity heavily but not excessively.

  17. Stress dependence of oxygen diffusion in ZrO2 film

    International Nuclear Information System (INIS)

    Yamamoto, Yasunori; Morishita, Kazunori; Iwakiri, Hirotomo; Kaneta, Yasunori

    2013-01-01

    First principles calculations were performed to evaluate the effect of stress on the diffusion process of oxygen atoms in monoclinic and tetragonal ZrO 2 . The formation and migration energies of an oxygen vacancy were obtained as a function of applied stress. Our results show that the formation and migration energies increase when the compressive stress is applied, which causes a reduction in the diffusion coefficient of an oxygen atom in ZrO 2 . This may explain the experimental observation that the oxide film grows in proportion to the cubic root of time

  18. The influence of charge transfers effects in monazite-type LaVO{sub 4} and perovskite-type LaVO{sub 3} prepared by sol-gel acrylamide polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Herrera-Pérez, G., E-mail: guillermo.herrera@cimav.edu.mx [CONACYT Research Fellow. Centro de Investigación en Materiales Avanzados (CIMAV), Miguel de Cervantes 120, Chihuahua 31136, Chihuahua (Mexico); Jiménez-Mier, J. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 Mexico D. F (Mexico); Yang, W.-L. [The Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Reyes-Rojas, A.; Fuentes-Cobas, L.E. [Department of Physics of Materials Department. Centro de Investigación en Materiales Avanzados (CIMAV), Miguel de Cervantes 120, Chihuahua 31136, Chihuahua (Mexico)

    2016-08-15

    Highlights: • We elucidate the electronic structure through the vanadium L{sub 2,3} edge in LaVO{sub 4} by XAS. • The interpretation of XAS spectrum was performed by the multiplet calculation. • Our results suggest that LaVO{sub 4} can be considered in the charge transfer regime. - Abstract: Core-hole spectroscopy such as X-ray absorption spectroscopy (XAS) is useful to determine the electronic structure of strongly correlated and strongly hybridized compounds such as vanadates. Monazite-type LaVO{sub 4} and perovskite-type LaVO{sub 3} are good candidates to elucidate the electronic structure through the vanadium L{sub 2,3} edge. LaVO{sub 4} was prepared by sol-gel acrylamide polymerization and solid-state reaction. LaVO{sub 3} was obtained by reduction of LaVO{sub 4} using Zr as gatherer. Monoclinic crystal phase for LaVO{sub 4} and orthorhombic crystal phase for LaVO{sub 3} were confirmed by the Rietveld refinement of X-ray diffraction patterns. XAS comparison between Vanadium L{sub 2,3} edge confirms the presence of V{sup 5+} for the monazite and V{sup 3+} for the orthorhombic perovskite. Multiplet calculations including crystal field and charge transfer effects (CTM) were performed in order to elucidate the tetragonal (D{sub 4h} symmetry) parameters Dq, Ds and Dt, the charge transfer energy Δ, and d-d Coulomb repulsion energy U parameters. CTM confirms for LaVO{sub 3} the strong V 3d–O 2p hybridization with a significant contribution of covalent character due to the delocalization of 3d electrons. For LaVO{sub 4} this work suggest the reclassification of this band insulator as charge transfer insulator that shows a significant contribution of ionic character.

  19. Simulation of vacancy migration energy in Cu under high strain

    International Nuclear Information System (INIS)

    Sato, K.; Yoshiie, T.; Satoh, Y.; Xu, Q.; Kiritani, M.

    2003-01-01

    The activation energy for the migration of vacancies in Cu under high strain was calculated by computer simulation using static methods. The migration energy of vacancies was 0.98 eV in the absence of deformation. It varied with the migration direction and stress direction because the distance between a vacancy and its neighboring atoms changes by deformation. For example, the migration energy for the shortest migration distance was reduced to 9.6 and 39.4% of its initial value by 10% compression and 20% elongation, respectively, while that for the longest migration distance was raised to 171.7 by 20% elongation. If many vacancies are created during high-speed deformation, the lowering of migration energy enables vacancies to escape to sinks such as surfaces, even during the shorter deformation period. The critical strain rate above which the strain rate dependence of vacancy accumulation ceases to exist increases with the lowering of vacancy migration energy

  20. Interaction of oxygen with zirconia surface

    International Nuclear Information System (INIS)

    Ivankiv, L.I.; Ketsman, I.V.

    1999-01-01

    The influence of surface heat treatment, electron (50-800) eV irradiation and UV (180-300) nM illumination of adsorption system on the state of oxygen adsorbed on zirconia surface have been investigated. On the basis of experimental results obtained by investigation of photon emission accompanying oxygen adsorption (AL) and TPD data existence of adsorption sites on the surface is suggested on which irreversible dissociative adsorption of oxygen occurs. These very sites are associated with emission processes Conclusion is made that the only type of adsorption sites connected with anion vacancy is present on zirconia surface and this is its charge state that determines the state of adsorbed oxygen. One of the important mechanisms by which the electron and UV photon excitation affects the adsorption interaction is the change of the charge state of the adsorption site

  1. BiVO4 nanoparticles: Preparation, characterization and photocatalytic activity

    Directory of Open Access Journals (Sweden)

    Venkataraman Sivakumar

    2015-12-01

    Full Text Available Bismuth vanadate (BiVO4 nanoparticles were synthesized by a simple thermal decomposition method. The synthesized bismuth vanadate nanoparticles were characterized by X-ray diffraction analysis, it is found that the synthesized sample belongs to monoclinic BiVO4. Fourier transform infrared spectroscopy confirms the formation of Bi-O bond in the sample. Ultraviolet–Visible (DRS-UV–Visible spectroscopy and photoluminescence spectroscopy reveal the optical property of the BiVO4 nanoparticles. The morphology was identified by both scanning electron microscopy and high-resolution transmission electron microscopy. Further, the photocatalytic activity of BiVO4 nanoparticles was investigated by photodegradation of methylene blue as a model organic pollutant.

  2. Large bandgap narrowing in rutile TiO2 aimed towards visible light applications and its correlation with vacancy-type defects history and transformation

    Science.gov (United States)

    Nair, Radhika V.; Gayathri, P. K.; Siva Gummaluri, Venkata; Nambissan, P. M. G.; Vijayan, C.

    2018-01-01

    Extension of photoactivity of TiO2 to the visible region is achievable via effective control over the intrinsic defects such as oxygen and Ti vacancies, which has several applications in visible photocatalysis and sensing. We present here the first observation of an apparent bandgap narrowing and bandgap tuning effect due to vacancy cluster transformation in rutile TiO2 structures to 1.84 eV from the bulk bandgap of 3 eV. A gradual transformation of divacancies (V Ti-O) to tri vacancies ({{V}Ti-O-T{{i-}}} ) achieved through a controlled solvothermal scheme appears to result in an apparent narrowing bandgap and tunability, as supported by positron annihilation lifetime and electron paramagnetic resonance spectroscopy measurements. Visible photocatalytic activity of the samples is demonstrated in terms of photodegradation of rhodamine B dye molecules.

  3. Scavenging of oxygen vacancies at modulation-doped oxide interfaces: Evidence from oxygen isotope tracing

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Döbeli, M.; Pomjakushina, E.

    2017-01-01

    , the mechanisms underlying the extreme mobility enhancement remain elusive. Herein, we used 18O isotope exchanged SrTi18O3 as substrates to create 2DEG at room temperature with and without the LSMO buffer layer. By mapping the oxygen profile across the interface between STO18 and disordered LaAlO3 or yttria...

  4. Adjacent Fe-Vacancy Interactions as the Origin of Room Temperature Ferromagnetism in (In(1-x)Fe(x))2O3.

    Science.gov (United States)

    Green, R J; Regier, T Z; Leedahl, B; McLeod, J A; Xu, X H; Chang, G S; Kurmaev, E Z; Moewes, A

    2015-10-16

    Dilute magnetic semiconductors (DMSs) show great promise for applications in spin-based electronics, but in most cases continue to elude explanations of their magnetic behavior. Here, we combine quantitative x-ray spectroscopy and Anderson impurity model calculations to study ferromagnetic Fe-substituted In2O3 films, and we identify a subset of Fe atoms adjacent to oxygen vacancies in the crystal lattice which are responsible for the observed room temperature ferromagnetism. Using resonant inelastic x-ray scattering, we map out the near gap electronic structure and provide further support for this conclusion. Serving as a concrete verification of recent theoretical results and indirect experimental evidence, these results solidify the role of impurity-vacancy coupling in oxide-based DMSs.

  5. Integrating the IA2 Astronomical Archive in the VO: The VO-Dance Engine

    Science.gov (United States)

    Molinaro, M.; Laurino, O.; Smareglia, R.

    2012-09-01

    Virtual Observatory (VO) protocols and standards are getting mature and the astronomical community asks for astrophysical data to be easily reachable. This means data centers have to intensify their efforts to provide the data they manage not only through proprietary portals and services but also through interoperable resources developed on the basis of the IVOA (International Virtual Observatory Alliance) recommendations. Here we present the work and ideas developed at the IA2 (Italian Astronomical Archive) data center hosted by the INAF-OATs (Italian Institute for Astrophysics - Trieste Astronomical Observatory) to reach this goal. The core point is the development of an application that from existing DB and archive structures can translate their content to VO compliant resources: VO-Dance (written in Java). This application, in turn, relies on a database (potentially DBMS independent) to store the translation layer information of each resource and auxiliary content (UCDs, field names, authorizations, policies, etc.). The last token is an administrative interface (currently developed using the Django python framework) to allow the data center administrators to set up and maintain resources. This deployment, platform independent, with database and administrative interface highly customizable, means the package, when stable and easily distributable, can be also used by single astronomers or groups to set up their own resources from their public datasets.

  6. Kinetic Monte Carlo Simulation of Oxygen and Cation Diffusion in Yttria-Stabilized Zirconia

    Science.gov (United States)

    Good, Brian

    2011-01-01

    Yttria-stabilized zirconia (YSZ) is of interest to the aerospace community, notably for its application as a thermal barrier coating for turbine engine components. In such an application, diffusion of both oxygen ions and cations is of concern. Oxygen diffusion can lead to deterioration of a coated part, and often necessitates an environmental barrier coating. Cation diffusion in YSZ is much slower than oxygen diffusion. However, such diffusion is a mechanism by which creep takes place, potentially affecting the mechanical integrity and phase stability of the coating. In other applications, the high oxygen diffusivity of YSZ is useful, and makes the material of interest for use as a solid-state electrolyte in fuel cells. The kinetic Monte Carlo (kMC) method offers a number of advantages compared with the more widely known molecular dynamics simulation method. In particular, kMC is much more efficient for the study of processes, such as diffusion, that involve infrequent events. We describe the results of kinetic Monte Carlo computer simulations of oxygen and cation diffusion in YSZ. Using diffusive energy barriers from ab initio calculations and from the literature, we present results on the temperature dependence of oxygen and cation diffusivity, and on the dependence of the diffusivities on yttria concentration and oxygen sublattice vacancy concentration. We also present results of the effect on diffusivity of oxygen vacancies in the vicinity of the barrier cations that determine the oxygen diffusion energy barriers.

  7. Current Status of VO Compliant Data Service in Japanese Virtual Observatory

    Science.gov (United States)

    Shirasaki, Y.; Komiya, Y.; Ohishi, M.; Mizumoto, Y.; Ishihara, Y.; Tsutsumi, J.; Hiyama, T.; Nakamoto, H.; Sakamoto, M.

    2012-09-01

    In these years, standards to build a Virtual Observatory (VO) data service have been established with the efforts in the International Virtual Observatory Alliance (IVOA). We applied these newly established standards (SSAP, TAP) to our VO service toolkit which was developed to implement earlier VO standards SIAP and (deprecated) SkyNode. The toolkit can be easily installed and provides a GUI interface to construct and manage VO service. In this paper, we describes the architecture of our toolkit and how it is used to start hosting VO service.

  8. Mechanical control of magnetism in oxygen deficient perovskite SrTiO3.

    Science.gov (United States)

    Zhang, Yajun; Wang, Jie; Sahoo, M P K; Shimada, Takahiro; Kitamura, Takayuki

    2015-10-28

    Mechanical control of magnetism in perovskite oxides is an important and promising approach in spintronics. Based on the first-principles calculations, we demonstrate that a negative pressure leads to a great enhancement of magnetic moment in deficient SrTiO3 with oxygen vacancies, whereas a positive pressure results in the gradual disappearance of magnetism. Spin charge density, Bader charge analysis and electronic density of states successfully elucidate the origin and underlying physics of the enhancement and disappearance of magnetism. It is found that the split electronic states of dz(2), dyz and dzx in the 3d orbitals of Ti atoms remarkably contribute to the occupancy of majority spin states under negative pressure, which induces a large magnetic moment. Under positive pressure, however, the equal occupancy of both majority and minority t2g and eg states leads to the disappearance of magnetization. In addition, both negative and positive pressures can largely lower the vacancy formation enthalpy, suggesting that the oxygen vacancy is preferable with pressure. Our findings may provide a mechanism to achieve the pressure control of magnetization in nonmagnetic perovskite oxides.

  9. Macroscopic results for a novel oxygenated silicon material

    CERN Document Server

    Watts, S J; Karpenko, A

    2002-01-01

    High-resistivity FZ silicon diodes have been processed in order to increase their oxygen dimer (O sub 2 sub i) concentration. Deep level transient spectroscopy measurements have been performed after proton irradiation showing that the formation of the VO centre is suppressed. The substrates had a starting resistivity of 2-4 k OMEGA cm, with an oxygen concentration of 10 sup 1 sup 5 and 10 sup 1 sup 7 cm sup - sup 3. Results for doping changes, leakage current and annealing behaviour after irradiation with 24 GeV/c protons are shown.

  10. HIGHER PRECISION OF HEART RATE COMPARED WITH VO2 TO PREDICT EXERCISE INTENSITY IN ENDURANCE-TRAINED RUNNERS

    Directory of Open Access Journals (Sweden)

    Victor M. Reis

    2011-03-01

    Full Text Available The aim of the present study was to assess the precision of oxygen uptake with heart rate regression during track running in highly-trained runners. Twelve national and international level male long-distance road runners (age 30.7 ± 5.5 yrs, height 1.71 ± 0.04 m and mass 61.2 ± 5.8 kg with a personal best on the half marathon of 62 min 37 s ± 1 min 22 s participated in the study. Each participant performed, in an all-weather synthetic track five, six min bouts at constant velocity with each bout at an increased running velocity. The starting velocity was 3.33 m·s-1 with a 0.56 m·s-1 increase on each subsequent bout. VO2 and heart rate were measured during the runs and blood lactate was assessed immediately after each run. Mean peak VO2 and mean peak heart rate were, respectively, 76.2 ± 9.7 mL·kg-1·min-1 and 181 ± 13 beats·min-1. The linearity of the regressions between heart rate, running velocity and VO2 were all very high (r > 0.99 with small standard errors of regression (i.e. Sy.x < 5% at the velocity associated with the 2 and 4 mmol·L-1 lactate thresholds. The strong relationships between heart rate, running velocity and VO2 found in this study show that, in highly trained runners, it is possible to have heart rate as an accurate indicator of energy demand and of the running speed. Therefore, in this subject cohort it may be unnecessary to use VO2 to track changes in the subjects' running economy during training periods.

  11. Effects of chronic nitric oxide synthase inhibition on V'O2max and exercise capacity in mice.

    Science.gov (United States)

    Wojewoda, M; Przyborowski, K; Sitek, B; Zakrzewska, A; Mateuszuk, L; Zoladz, J A; Chlopicki, S

    2017-03-01

    Acute inhibition of NOS by L-NAME (N ω -nitro-L-arginine methyl ester) is known to decrease maximal oxygen consumption (V'O 2max ) and impair maximal exercise capacity, whereas the effects of chronic L-NAME treatment on V'O 2max and exercise performance have not been studied so far. In this study, we analysed the effect of L-NAME treatment, (LN2 and LN12, respectively) on V'O 2max and exercise capacity (in maximal incremental running and prolonged sub-maximal incremental running tests), systemic NO bioavailability (plasma nitrite (NO 2 - ) and nitrate (NO 3 - )) and prostacyclin (PGI 2 ) production in C57BL6/J mice. Mice treated with L-NAME for 2 weeks (LN2) displayed higher V'O 2max and better running capacity than age-matched control mice. In LN2 mice, NO bioavailability was preserved, as evidenced by maintained NO 2 - plasma concentration. PGI 2 production was activated (increased 6-keto-PGF 1α plasma concentration) and the number of circulating erythrocytes (RBC) and haemoglobin concentration were increased. In mice treated with L-NAME for 12 weeks (LN12), NO bioavailability was decreased (lower NO 2 - plasma concentration), and 6-keto-PGF 1α plasma concentration and RBC number were not elevated compared to age-matched control mice. However, LN12 mice still performed better during the maximal incremental running test despite having lower V'O 2max . Interestingly, the LN12 mice showed poorer running capacity during the prolonged sub-maximal incremental running test. To conclude, short-term (2 weeks) but not long-term (12 weeks) treatment with L-NAME activated robust compensatory mechanisms involving preservation of NO2- plasma concentration, overproduction of PGI 2 and increased number of RBCs, which might explain the fully preserved exercise capacity despite the inhibition of NOS.

  12. Vacancy defect and defect cluster energetics in ion-implanted ZnO

    Science.gov (United States)

    Dong, Yufeng; Tuomisto, F.; Svensson, B. G.; Kuznetsov, A. Yu.; Brillson, Leonard J.

    2010-02-01

    We have used depth-resolved cathodoluminescence, positron annihilation, and surface photovoltage spectroscopies to determine the energy levels of Zn vacancies and vacancy clusters in bulk ZnO crystals. Doppler broadening-measured transformation of Zn vacancies to vacancy clusters with annealing shifts defect energies significantly lower in the ZnO band gap. Zn and corresponding O vacancy-related depth distributions provide a consistent explanation of depth-dependent resistivity and carrier-concentration changes induced by ion implantation.

  13. On the stability and mobility of di-vacancies in tungsten

    Science.gov (United States)

    Heinola, K.; Djurabekova, F.; Ahlgren, T.

    2018-02-01

    Properties of small vacancy clusters in tungsten were studied with first-principles calculations. The binding and formation energies of the vacancy clusters increase with the cluster size. Dynamic characteristics of a di-vacancy were specified between room temperature and 700 K with lattice kinetic Monte Carlo calculations, which were parametrised with the present first-principles results for the dissociation barriers. An Arrhenius fit for the di-vacancy diffusion yielded \

  14. The effect of urinary cadmium on cardiovascular fitness as measured by VO2 max in white, black and Mexican Americans

    International Nuclear Information System (INIS)

    Egwuogu, Heartley; Shendell, Derek G.; Okosun, Ike S.; Goodfellow, Lynda

    2009-01-01

    Objectives: We explored potential effects of cadmium exposure on cardiovascular fitness measures, including gender and racial/ethnic differences. Methods: Data were from the 1999 to 2000 National Health and Nutrition Examination Survey (NHANES); 1963 participating subjects were included in our analysis. Volume of oxygen consumed at sub-maximum activity (VO 2 max) were recorded in a series of graded exercises; the goal was to elicit 75% of predetermined age-specific heart rates. Cadmium from urine samples was measured in the laboratory using standard methods. Multivariate linear regression analyses were performed to determine potential relationships. Results: Increased urinary cadmium concentrations were generally associated with decreased estimated VO 2 max values. Gender and racial/ethnic differences were also observed. Specifically, associations were statistically significant for white males and Mexican American females. Conclusion: Inverse associations between urinary cadmium concentrations and estimated VO 2 max values were observed, including racial and gender differences. The implications of such gender and racial/ethnic differences on long-term cardiovascular health and health disparities of present public health concern warrant further investigation

  15. Double K-vacancy production by x-ray photoionization

    International Nuclear Information System (INIS)

    Southworth, S. H.; Dunford, R. W.; Kanter, E. P.; Krassig, B.; Young, L.; Armen, G. B.; Levin, J. C.; Chen, M. H.; Ederer, D. L.

    2002-01-01

    We have studied double K-shell photoionization of Ne and Mo (Z = 10 and 42) at the Advanced Photon Source. Double K-vacancy production in Ne was observed by recording the KK-KLL Auger hypersatellite spectrum. Comparison is made with calculations using the multiconfiguration Dirac-Fock method. For Mo, double K-vacancy production was observed by recording the Kα, β fluorescence hypersatellite and satellite x rays in coincidence. From the intensities of the Auger or x-ray hypersatellites relative to diagram lines, the probabilities for double K-vacancy production relative to single K-vacancies were determined. These results, along with reported measurements on other atoms, are compared with Z-scaling calculations of the high-energy limits of the double-to-single K-shell photoionization ratio

  16. Mobile telephones: a comparison of radiated power between 3G VoIP calls and 3G VoCS calls.

    Science.gov (United States)

    Jovanovic, Dragan; Bragard, Guillaume; Picard, Dominique; Chauvin, Sébastien

    2015-01-01

    The purpose of this study is to assess the mean RF power radiated by mobile telephones during voice calls in 3G VoIP (Voice over Internet Protocol) using an application well known to mobile Internet users, and to compare it with the mean power radiated during voice calls in 3G VoCS (Voice over Circuit Switch) on a traditional network. Knowing that the specific absorption rate (SAR) is proportional to the mean radiated power, the user's exposure could be clearly identified at the same time. Three 3G (High Speed Packet Access) smartphones from three different manufacturers, all dual-band for GSM (900 MHz, 1800 MHz) and dual-band for UMTS (900 MHz, 1950 MHz), were used between 28 July and 04 August 2011 in Paris (France) to make 220 two-minute calls on a mobile telephone network with national coverage. The places where the calls were made were selected in such a way as to describe the whole range of usage situations of the mobile telephone. The measuring equipment, called "SYRPOM", recorded the radiation power levels and the frequency bands used during the calls with a sampling rate of 20,000 per second. In the framework of this study, the mean normalised power radiated by a telephone in 3G VoIP calls was evaluated at 0.75% maximum power of the smartphone, compared with 0.22% in 3G VoCS calls. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR.

  17. Potassium vanadium selenite, K(VO2)3(SeO3)2

    International Nuclear Information System (INIS)

    Harrison, W.T.A.; Dussack, L.L.; Jacobson, A.J.

    1995-01-01

    The hydrothermal synthesis and single-crystal structure of potassium vanadium(V) selenite, K(VO 2 ) 3 (SeO 3 ) 2 , are reported. K(VO 2 ) 3 (SeO 3 ) 2 is a layered phase based on a hexagonal tungsten-oxide-like array of corner-sharing VO 6 octahedra capped by Se atoms, and is isostructural with NH 4 (VO 2 ) 3 (SeO 3 ) 2 . (orig.)

  18. Endurance training increases exercise-induced prostacyclin release in young, healthy men--relationship with VO2max.

    Science.gov (United States)

    Zoladz, Jerzy A; Majerczak, Joanna; Duda, Krzysztof; Chłopicki, Stefan

    2010-01-01

    In the present study, we evaluated the effect of 5 weeks of moderate-intensity endurance training on the basal and exercise-induced systemic release of prostacyclin (PGI(2)), as assessed by plasma 6-keto-PGF(1 alpha) concentration. Twelve physically active young men with the following characteristics participated in this study (the mean +/- SD): age, 22.7 +/- 2.0 years; body mass, 76.8 +/- 8.9 kg; BMI, 23.48 +/- 2.17 kg x m(-2); and maximal oxygen uptake (VO(2 max)), 46.1 +/- 4.0 ml x kg(-1) x min(-1). Plasma 6-keto-PGF(1 alpha) concentrations were measured in venous blood samples taken prior to the exercise and at exhaustion (at VO(2 max)) before and after completing the training protocol. On average, the training resulted in a significant increase in VO(2 max) (p = 0.03), power output at VO(2 max) (p = 0.001) and a significant increase (p = 0.05) in the net-exercise-induced increase in plasma 6-keto-PGF(1 alpha) concentration (Delta 6-keto-PGF(1 alpha) i.e., the difference between the end-exercise and pre-exercise 6-keto-PGF(1 alpha) concentrations). No effect of training on the basal PGI(2) concentration was found. Interestingly, within the study sample (n = 12), two subgroups could be defined with a differential pattern of response with respect to Delta 6-keto-PGF(1 alpha) concentrations. In one subgroup (n = 7), a significant increase in Delta 6-keto-PGF(1 alpha) concentration after training was found (p < 0.02) (responders). This enhancement in the exercise-induced PGI(2) release was accompanied by a significant (p < 0.05) increase in VO(2 max) after training. In contrast, in another subgroup (n = 5), there was no observed effect of training on the Delta 6-keto-PGF(1 alpha) concentration and the VO(2 max) after training (non-responders). In both of these subgroups, training did not influence the basal PGI(2) concentration. In conclusion, the endurance training resulted in the adaptive augmentation of the systemic release of PGI(2) in response to exercise

  19. Seasonal variation of VO 2 max and the VO2-work rate relationship in elite Alpine skiers.

    Science.gov (United States)

    Gross, Micah A; Breil, Fabio A; Lehmann, Andrea D; Hoppeler, Hans; Vogt, Michael

    2009-11-01

    Alpine ski performance relates closely to both anaerobic and aerobic capacities. During their competitive season, skiers greatly reduce endurance and weight training, and on-snow training becomes predominant. To typify this shift, we compared exhaustive ramp cycling and squat (SJ) and countermovement jumping (CMJ) performance in elite males before and after their competitive season. In postseason compared with preseason: 1) maximal oxygen uptake (VO 2 max) normalized to bodyweight was higher (55.2 +/- 5.2 vs 52.7 +/- 3.6 mL x kg(-1) x min(-1), P jump height was greater in SJ (47.4 +/- 4.4 vs 44.7 +/- 4.3 cm, P skiing seemingly provides an ample cardiovascular training stimulus for skiers to maintain their aerobic capacities during the racing season. We conclude that aerobic fitness and leg explosiveness can be maintained in-season but may be compromised by heavy or excessive preseason training. In addition, ramp test V O2/W slope analysis could be useful for monitoring both positive and negative responses to training.

  20. A comparison of methods of predicting maximum oxygen uptake.

    OpenAIRE

    Grant, S; Corbett, K; Amjad, A M; Wilson, J; Aitchison, T

    1995-01-01

    The aim of this study was to compare the results from a Cooper walk run test, a multistage shuttle run test, and a submaximal cycle test with the direct measurement of maximum oxygen uptake on a treadmill. Three predictive tests of maximum oxygen uptake--linear extrapolation of heart rate of VO2 collected from a submaximal cycle ergometer test (predicted L/E), the Cooper 12 min walk, run test, and a multi-stage progressive shuttle run test (MST)--were performed by 22 young healthy males (mean...

  1. Oxygen vacancies effect on ionic conductivity and relaxation phenomenon in undoped and Mn doped PZN-4.5PT single crystals

    International Nuclear Information System (INIS)

    Kobor, Diouma; Guiffard, Benoit; Lebrun, Laurent; Hajjaji, Abdelowahed; Guyomar, Daniel

    2007-01-01

    AC-impedance spectroscopic studies in the temperature range 550-700 deg. C are carried out on undoped and Mn doped PZN-PT single crystals grown by the flux method. The variation of dielectric permittivity with temperature at different frequencies shows normal ferroelectric and relaxor-like dependence for the doped and undoped crystals, respectively. Temperature-dependent spectroscopic modulus plots reveal a much broader peak for PZN-4.5PT + 1%Mn compared with that for PZN-4.5PT, which is different from the dielectric behaviour of the doped one. Complex modulus imaginary part (Z-prime) versus real part (Z') plots fit well with one semicircle thus indicating only bulk contribution. The relaxation observed in the spectroscopic plots was assigned to mobile relaxor species such as oxygen vacancies and ions. No such relaxation could be observed for PZN-4.5PT + 1%Mn in the dielectric measurements. For both undoped and Mn doped crystals, the conduction behaviour was modelled by the universal dynamic response equation and by the NTC (negative temperature coefficient) materials resistance-temperature behaviour. A large difference in behaviour was found between the two single crystals such as the thermistor coefficients and the activation energy values, which could explain the increase in the thermal stability observed in the Mn doped PZN-PT single crystals by many studies

  2. Synthesis of sub-10 nm VO{sub 2} nanoparticles films with plasma-treated glass slides by aqueous sol–gel method

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Shi-Di [Department of Materials Science and Engineering, National Taiwan University of Science and Technology, 43, Sec. 4, Keelung Rd, Taipei 106, Taiwan, ROC (China); Cheng, Chih-Chia [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan (China); Huang, Chi-Hsien [Department of Materials Engineering, Ming Chi University of Technology, 84 Gungjuan Road, Taishan Dist., New Taipei City 24301, Taiwan (China); Chen, Jem-Kun, E-mail: jkchen@mail.ntust.edu.tw [Department of Materials Science and Engineering, National Taiwan University of Science and Technology, 43, Sec. 4, Keelung Rd, Taipei 106, Taiwan, ROC (China)

    2015-12-01

    Highlights: • Sub-10 nm VO{sub 2} nanoparticles (VNPs) are synthesized on a plasma-treated glass. • Glass slides generate negative charges sites after plasma treatment to attract VO{sub 2}{sup +}. • Doping tungsten with 1 wt% in VNPs did not change particle size significantly. • The particle size of VNP can be tuned by the density of negative charge sites. • Sub-10 nm structured VO{sub 2} particle films exhibited high visible transmittance. - Abstract: This paper describes an aqueous sol–gel synthesis of thermochromic thin films consisted of vanadium dioxide nanoparticles (VNPs) on glass slides. The glass slides were treated by argon/oxygen plasma to generate dispersedly negative charge sites on the surface to attract VO{sub 2}{sup +} from a sol–gel solution. After heat treatment in a low-pressure carbon monoxide/carbon dioxide (CO/CO{sub 2}) atmosphere, the VNPs could be generated in sub-10 nm of particle size on the surface. Various levels of doping were achieved by adding small quantities of a water-soluble tungsten compound to the sol; however, the particle size increased slightly with the tungsten doping levels. The change in electrical conductivity with temperature for VNP films were measured and compared to VO{sub 2} crystalline films. VNP films exhibited the lower transition temperature of the semiconductor to metal phase change; at a doping level of 4 wt% the transition temperature was measured at 32.2 ± 1.2 and 24.1 ± 1.2 °C for the VO{sub 2} and VNP films, respectively. The VNP films showed excellent visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal–insulator phase transition (MIT). The current method is a landmark in the development of nanostructured material toward applications in energy-saving smart windows.

  3. Moessbauer effect and vacancy diffusion

    International Nuclear Information System (INIS)

    Gunther, L.

    1976-01-01

    A dynamical theory of vacancy diffusion which was motivated by the need to explain recent experimental results for the Moessbauer spectra of Fe in Cu, Fe in Au and Fe in Al is presented. Diffusion in these systems is dominated by the vacancy mechanism, which involves strong correlations between successive jumps. The theory developed by Singwi and Sjoelander for the Moessbauer spectrum of a diffusing nucleus is therefore not applicable. The inverse of the normalized Moessbauer spectrum evaluated at zero frequency is introduced as a useful means of comparing experimental with theoretical spectral widths

  4. Study of LiNiVO{sub 4} thin films used as anodes in lithium micro-batteries; Etude de couches minces de type LiNiVO{sub 4} utilisables en tant qu'electrode negative dans des microbatteries au lithium

    Energy Technology Data Exchange (ETDEWEB)

    Reddy, V.

    2003-03-01

    Since fifteen years, considerable effort has been invested in developing thin film solid state micro-batteries as possible integrated components in microelectronics. The recent technological improvement concerning miniaturized systems opens a large field of applications for the future use of micro-batteries. LiNiVO{sub 4} thin films are promising materials as anodes for lithium micro-batteries. All the thin films have been prepared by radio-frequency magnetron sputtering using a LiNiVO{sub 4} target. The discharge gas was either pure argon or a mixture of argon and oxygen. We have studied the influence of some experimental parameters such as the oxygen partial pressure, the sputtering power, the target-substrate distance, the total pressure and the substrate temperature on the composition, the microstructure and the electrochemical properties. The chemical composition of the thin films has been determined by Rutherford backscattering spectroscopy combined with nuclear reaction analysis. Among all experimental parameters investigated, only the partial pressure of oxygen has a considerable influence on the thin film composition. Auger spectroscopy has revealed a good homogeneity of the thin films. X-ray diffraction shows that the as-deposited thin films are amorphous. The near-stoichiometric composition Li{sub 1.12}NiV{sub 1.02}O{sub 4}.11 has highlighted good electrochemical properties in the potential range [3 V - 0.02 V]. This particular composition displays a high capacity of 1000 mAh/g which is enhanced when the film is annealed at 300 degrees C. (author)

  5. Effect of wearing clothes on oxygen uptake and ratings of perceived exertion while swimming.

    Science.gov (United States)

    Choi, S W; Kurokawa, T; Ebisu, Y; Kikkawa, K; Shiokawa, M; Yamasaki, M

    2000-07-01

    For a comparative study between swimming in swimwear (control-sw) and swimming in clothes (clothes-sw), oxygen uptake (VO2) and ratings of perceived exertion (RPE) were measured. The subjects were six male members of a university swimming team. Three swimming strokes--the breaststroke, the front crawl stroke and the elementary backstroke--were applied. With regards to clothes-sw, swimmers wore T-shirts, sportswear (shirt and pants) over swimwear and running shoes. In both cases of control-sw and clothes-sw, the VO2 was increased exponentially with increased swimming speed. The VO2 of the subjects during the clothed tests did not exceed 1.4 times of that in the case of control-sw at swimming speeds below 0.3 m/s. As swimming speeds increased, VO2 difference in both cases increased. Consequently, VO2 in the clothed tests was equal to 1.5-1.6 times and 1.5-1.8 times of that in the swimwear tests at speeds of 0.5 and 0.7 m/s, respectively. At speeds below 0.6 m/s in clothes-sw, the breaststroke showed lower VO2 than the front crawl stroke, and the elementary backstroke showed higher VO2 than the other two swimming strokes. RPE increased linearly with %peak VO2. In addition, any RPE differences among the three swimming strokes were not shown in the control-sw tests. At an exercise intensity above 60 %peak VO2, clothed swimmers showed slightly higher RPE in the front crawl stroke compared to that in the two other swimming strokes.

  6. A vacancy-modulated self-selective resistive switching memory with pronounced nonlinear behavior

    Science.gov (United States)

    Ma, Haili; Feng, Jie; Gao, Tian; Zhu, Xi

    2017-12-01

    In this study, we report a self-selective (nonlinear) resistive switching memory cell, with high on-state half-bias nonlinearity of 650, sub-μA operating current, and high On/Off ratios above 100×. Regarding the cell structure, a thermal oxidized HfO x layer in combination with a sputtered Ta2O5 layer was configured as an active stack, with Pt and Hf as top and bottom electrodes, respectively. The Ta2O5 acts as a selective layer as well as a series resistor, which could make the resistive switching happened in HfO x layer. Through the analysis of the physicochemical properties and electrical conduction mechanisms at each state, a vacancy-modulated resistance switching model was proposed to explain the switching behavior. The conductivity of HfO x layer was changed by polarity-dependent drift of the oxygen vacancy ( V o), resulting in an electron hopping distance change during switching. With the help of Ta2O5 selective layer, high nonlinearity observed in low resistance state. The proposed material stack shows a promising prospect to act as a self-selective cell for 3D vertical RRAM application.

  7. Using VO Concept for Managing Dynamic Security Associations

    NARCIS (Netherlands)

    Demchenko, Y.; Gommans, L.; de Laat, C.T.A.M.

    2006-01-01

    This research paper presents results of the analysis how the Virtual Organisation (VO) concept can be used for managing dynamic security associations in collaborative applications and for complex resource provisioning. The paper provides an overview of the current practice in VO management at the

  8. Research progress of VO2 thin film as laser protecting material

    Science.gov (United States)

    Liu, Zhiwei; Lu, Yuan; Hou, Dianxin

    2018-03-01

    With the development of laser technology, the battlefield threat of directional laser weapons is becoming more and more serious. The blinding and destruction caused by laser weapons on the photoelectric equipment is an important part of the current photo-electronic warfare. The research on the defense technology of directional laser weapons based on the phase transition characteristics of VO2 thin films is an important subject. The researches of VO2 thin films are summarized based on review these points: the preparation methods of VO2 thin films, phase transition mechanism, phase transition temperature regulating, interaction between VO2 thin films and laser, and the application prospect of vo2 thin film as laser protecting material. This paper has some guiding significance for further research on the VO2 thin films in the field of defense directional laser weapons.

  9. Oxygen nonstoichiometry and defects in Mn-doped Gd2Ti2O7+x

    International Nuclear Information System (INIS)

    Porat, O.; Tuller, H.L.

    1996-01-01

    The oxygen nonstoichiometry in Mn-doped Gd 2 Ti 2 O 7 , Gd 2 (Ti 0.975 Mn 0.025 ) 2 O 7+x , was measured electrochemically, as a function of temperature and oxygen partial pressure, with the aid of an oxygen titration cell. The analysis of the data shows that the defect equilibrium can be described by considering the dominant point defects to be neutral oxygen interstitials, doubly charged oxygen vacancies, and trivalent and quadrivalent Mn ions substituted in the Ti sites. The enthalpies for the formation of neutral oxygen interstitials and trivalent Mn are determined

  10. Stress dependence of oxygen diffusion in ZrO{sub 2} film

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, Yasunori, E-mail: yasu-yamamoto@iae.kyoto-u.ac.jp [Graduate School of Energy Science, Kyoto University, Uji, Kyoto 611-0011 (Japan); Morishita, Kazunori [Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan); Iwakiri, Hirotomo [Faculty of Education, University of the Ryukyus, Nakagami-gun, Okinawa 903-0213 (Japan); Kaneta, Yasunori [Akita National College of Technology, Akita, Akita 011-8511 (Japan)

    2013-05-15

    First principles calculations were performed to evaluate the effect of stress on the diffusion process of oxygen atoms in monoclinic and tetragonal ZrO{sub 2}. The formation and migration energies of an oxygen vacancy were obtained as a function of applied stress. Our results show that the formation and migration energies increase when the compressive stress is applied, which causes a reduction in the diffusion coefficient of an oxygen atom in ZrO{sub 2}. This may explain the experimental observation that the oxide film grows in proportion to the cubic root of time.

  11. High quality diesel fuels by VO-LSGO hydrotreatment

    Energy Technology Data Exchange (ETDEWEB)

    Stanica-Ezeanu, Dorin; Juganaru, Traian [Petroleum and Gas Univ. of Ploiesti (Romania)

    2013-06-01

    The aim of the paper is to obtain a high quality Diesel fuel by hydro-deoxigenation of vegetable oils (VO) mixed with a low sulfur gasoil (LSGO). The process is possible by using a bi-functional catalyst Ni-Mo supported by an activated Al{sub 2}O{sub 3} containing 2% Ultrastable Y-zeolite. The experimental conditions were: T =340 - 380 C, Pressure = 50 bar, LHSV = 1,5 h{sup -1}, H{sub 2}/Feed ratio = 15 mole H{sub 2} /mole liquid feed. The liquid product was separated in two fractions: a light distillate (similar to gasoline) and a heavy distillate (boiling point > 200 C) with very good characteristics for Diesel engines. The reaction chemistry is very complex, but the de-oxygenation process is decisive for the chemical structure of hydrocarbons from final product. Finally, a schema for the reaction mechanism is proposed. (orig.)

  12. The effect of a peer on VO2 and game choice in 6-10 year old children

    Directory of Open Access Journals (Sweden)

    Lee Anne Siegmund

    2014-06-01

    Full Text Available Relative to sedentary video games (e.g., Playstation 2 (PS2, playing physically active video games (e.g., Nintendo Wii (Wii significantly increases caloric expenditure in children. Studies have demonstrated that the presence of a peer increases physical activity in children. We sought to determine if children would expend more energy and find playing Wii more motivating than PS2 when with a peer. Seventeen children (age 8.5 ± 0.4 years rested, played PS2 and Wii Sports Boxing for 10 minutes each, in two conditions: one in which the children rested/played the games alone (alone condition and another in which they played with a peer (peer condition. Oxygen consumption (VO2, and liking (visual analog scale was assessed for each 10-minute condition. After three 10-minute resting/gaming conditions, motivation was assessed using a relative reinforcing value task (RRV in which children performed computer mouse presses to gain additional access for either PS2 or Wii. VO2 was greater (p Conclusion: The presence of a peer increased VO2 during Wii play for boys but not girls. Surprisingly, the presence of a peer decreased children’s motivation to play Wii versus PS2.

  13. Oxygen Consumption of Elite Distance Runners on an Anti-Gravity Treadmill®

    Directory of Open Access Journals (Sweden)

    David K.P. McNeill, John R. Kline, Hendrick D. de Heer, J. Richard Coast

    2015-06-01

    Full Text Available Lower body positive pressure (LBPP, or ‘anti-gravity’ treadmills® have become increasingly popular among elite distance runners. However, to date, few studies have assessed the effect of body weight support (BWS on the metabolic cost of running among elite runners. This study evaluated how BWS influenced the relationship between velocity and metabolic cost among 6 elite male distance runners. Participants ran three- 16 minute tests consisting of 4 stages of 4 minutes at 8, 7, 6 and 5 min·mile−1 pace (3.35, 3.84, 4.47 and 5.36 m·s−1, while maintaining an aerobic effort (Respiratory Exchange Ratio ≤1.00. One test was run on a regular treadmill, one on an anti-gravity treadmill with 40% BWS and one with 20% BWS being provided. Expired gas data were collected and regression equations used to determine and compare slopes. Significant decreases in oxygen uptake (V̇O2 were found with each increase in BWS (p < 0.001. At 20% BWS, the average decrease in net VO2 was greater than proportional (34%, while at 40% BWS, the average net reduction in VO2 was close to proportional (38%. Across velocities, the slope of the relationship between VO2 and velocity (ΔV̇O2/Δv was steeper with less support. The slopes at both the 20% and 40% BWS conditions were similar, especially when compared to the regular treadmill. Variability in VO2 between athletes was much greater on the LBPP treadmill and was greater with increased levels of BWS. In this study we evaluated the effect of body weight support on V̇O2 among elite distance runners. We have shown that oxygen uptake decreased with support, but not in direct proportion to that support. Further, because of the high variability in oxygen uptake between athletes on the LBPP treadmill, prediction equations may not be reliable and other indicators (heart rate, perceived exertion or directly measured oxygen uptake should be used to guide training intensity when training on the LBPP treadmill.

  14. Emergent Phenomena at Mott Interfaces

    Science.gov (United States)

    2016-11-03

    thickness for electron liquid formation in SrTiO3 embedded in GdTiO3, and standing-wave soft- and hard - x-ray photoemission to determine the energetic...Transition in VO2 by Electric Field-Induced Oxygen Vacancy Formation , Science, (03 2013): 1402. doi: 10.1126/science.1230512 L. Feigl, B.D. Schultz, S...S. Fadley. Band offsets in complex-oxide thin films and heterostructures ofSrTiO3/LaNiO3 and SrTiO3/GdTiO3 by soft and hard X-ray

  15. VACANCIES AND THE RECRUITMENT OF NEW EMPLOYEES

    NARCIS (Netherlands)

    VANOURS, J; RIDDER, G

    Little is known about the search strategy that employers use in their efforts to fill job vacancies. In this article, we analyze unique micro data to study this search strategy. We conclude that almost all vacancies are filled from a pool of applicants that is formed shortly after the posting of the

  16. ) m /SrVO3 ( m = 5, 6) Superlattices

    KAUST Repository

    Dai, Qingqing; Lü ders, Ulrike; Fré sard, Raymond; Eckern, Ulrich; Schwingenschlö gl, Udo

    2018-01-01

    The (LaV3+O3)m/SrV4+O3 (m = 5, 6) superlattices are investigated by first principles calculations. While bulk LaVO3 is a C‐type antiferromagnetic semiconductor and bulk SrVO3 is a paramagnetic metal, semiconducting A‐type antiferromagnetic states

  17. Assessing hafnium on hafnia as an oxygen getter

    International Nuclear Information System (INIS)

    O'Hara, Andrew; Demkov, Alexander A.; Bersuker, Gennadi

    2014-01-01

    Hafnium dioxide or hafnia is a wide band gap dielectric used in a range of electronic applications from field effect transistors to resistive memory. In many of these applications, it is important to maintain control over oxygen stoichiometry, which can be realized in practice by using a metal layer, specifically hafnium, to getter oxygen from the adjacent dielectric. In this paper, we employ density functional theory to study the thermodynamic stability of an interface between (100)-oriented monoclinic hafnia and hafnium metal. The nudged elastic band method is used to calculate the energy barrier for migration of oxygen from the oxide to the metal. Our investigation shows that the presence of hafnium lowers the formation energy of oxygen vacancies in hafnia, but more importantly the oxidation of hafnium through the migration of oxygen from hafnia is favored energetically

  18. Strain Relaxation and Vacancy Creation in Thin Platinum Films

    International Nuclear Information System (INIS)

    Gruber, W.; Chakravarty, S.; Schmidt, H.; Baehtz, C.; Leitenberger, W.; Bruns, M.; Kobler, A.; Kuebel, C.

    2011-01-01

    Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 deg. C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.

  19. Dissociative diffusion mechanism in vacancy-rich materials according to mass action kinetics

    Directory of Open Access Journals (Sweden)

    N. J. Biderman

    2016-05-01

    Full Text Available Two sets of diffusion-reaction numerical simulations using a finite difference method (FDM were conducted to investigate fast impurity diffusion via interstitial sites in vacancy-rich materials such as Cu(In,GaSe2 (CIGS and Cu2ZnSn(S, Se4 (CZTSSe or CZTS via the dissociative diffusion mechanism where the interstitial diffuser ultimately reacts with a vacancy to produce a substitutional. The first set of simulations extends the standard interstitial-limited dissociative diffusion theory to vacancy-rich material conditions where vacancies are annihilated in large amounts, introducing non-equilibrium vacancy concentration profiles. The second simulation set explores the vacancy-limited dissociative diffusion where impurity incorporation increases the equilibrium vacancy concentration. In addition to diffusion profiles of varying concentrations and shapes that were obtained in all simulations, some of the profiles can be fitted with the constant- and limited-source solutions of Fick’s second law despite the non-equilibrium condition induced by the interstitial-vacancy reaction. The first set of simulations reveals that the dissociative diffusion coefficient in vacancy-rich materials is inversely proportional to the initial vacancy concentration. In the second set of numerical simulations, impurity-induced changes in the vacancy concentration lead to distinctive diffusion profile shapes. The simulation results are also compared with published data of impurity diffusion in CIGS. According to the characteristic properties of diffusion profiles from the two set of simulations, experimental detection of the dissociative diffusion mechanism in vacancy-rich materials may be possible.

  20. Biobjective VoIP Service Management in Cloud Infrastructure

    Directory of Open Access Journals (Sweden)

    Jorge M. Cortés-Mendoza

    2016-01-01

    Full Text Available Voice over Internet Protocol (VoIP allows communication of voice and/or data over the internet in less expensive and reliable manner than traditional ISDN systems. This solution typically allows flexible interconnection between organization and companies on any domains. Cloud VoIP solutions can offer even cheaper and scalable service when virtualized telephone infrastructure is used in the most efficient way. Scheduling and load balancing algorithms are fundamental parts of this approach. Unfortunately, VoIP scheduling techniques do not take into account uncertainty in dynamic and unpredictable cloud environments. In this paper, we formulate the problem of scheduling of VoIP services in distributed cloud environments and propose a new model for biobjective optimization. We consider the special case of the on-line nonclairvoyant dynamic bin-packing problem and discuss solutions for provider cost and quality of service optimization. We propose twenty call allocation strategies and evaluate their performance by comprehensive simulation analysis on real workload considering six months of the MIXvoip company service.