Photoresponse in La0.9Hf0.1MnO3/0.05wt%Nb-doped SrTiO3 heteroepitaxial junctions

Science.gov (United States)

Qi, Yaping; Ni, Hao; Zheng, Ming; Zeng, Jiali; Jiang, Yucheng; Gao, Ju

2018-05-01

Excellent photo detectors need to have the rapid response and good repeatability from the requirement of industrial applications. In this paper, transport behavior and opto-response of heterostructures made with La0.9Hf0.1MnO3 and 0.05wt%Nb-doped SrTiO3 were investigated. The heterojunctions exhibited an excellent rectifying feature with very low leakage in a broad temperature region (from 40 to 300 K). These thin films presented persistent and stable photovoltages upon light illumination. Rapid shift between small and large voltages corresponding to "light OFF" and "light ON" states, respectively, was observed, demonstrating reliable photo detection behavior. A semiconductor laser with a wavelength of 650 nm was used as the light source. It is also noted that the observed photovoltages are strongly determined by light intensity. The injection of photoexcited charge carriers (electrons) could be responsible for the appearance of the observed opto-response. Such manipulative features by light irradiation exhibit great potential for light detectors for visible light.

Photoresponse in La0.9Hf0.1MnO3/0.05wt%Nb-doped SrTiO3 heteroepitaxial junctions

Directory of Open Access Journals (Sweden)

Yaping Qi

2018-05-01

Full Text Available Excellent photo detectors need to have the rapid response and good repeatability from the requirement of industrial applications. In this paper, transport behavior and opto-response of heterostructures made with La0.9Hf0.1MnO3 and 0.05wt%Nb-doped SrTiO3 were investigated. The heterojunctions exhibited an excellent rectifying feature with very low leakage in a broad temperature region (from 40 to 300 K. These thin films presented persistent and stable photovoltages upon light illumination. Rapid shift between small and large voltages corresponding to “light OFF” and “light ON” states, respectively, was observed, demonstrating reliable photo detection behavior. A semiconductor laser with a wavelength of 650 nm was used as the light source. It is also noted that the observed photovoltages are strongly determined by light intensity. The injection of photoexcited charge carriers (electrons could be responsible for the appearance of the observed opto-response. Such manipulative features by light irradiation exhibit great potential for light detectors for visible light.

Growth and physical properties of highly oriented La-doped (K,Na)NbO3 ferroelectric thin films

International Nuclear Information System (INIS)

Vendrell, X.; Raymond, O.; Ochoa, D.A.; García, J.E.; Mestres, L.

2015-01-01

Lead-free (K,Na)NbO 3 (KNN) and La doped (K,Na)NbO 3 (KNN-La) thin films are grown on SrTiO 3 substrates using the chemical solution deposition method. The effect of adding different amounts of Na and K excess (0–20 mol%) is investigated. The results confirm the necessity of adding 20 mol% excess amounts of Na and K precursor solutions in order to avoid the formation of the secondary phase, K 4 Nb 6 O 17 , as confirmed by X-ray diffraction and Raman spectroscopy. Moreover, when adding a 20 mol% of alkaline metal excess, the thin films are highly textured with out-of-plane preferential orientation in the [100] direction of the [100] orientation of the substrate. Doping with lanthanum results in a decrease of the leakage current density at low electric field, and an increase in the dielectric permittivity across the whole temperature range (80–380 K). Although the (100)-oriented KNN and KNN-La films exhibited rounded hysteresis loops, at low temperatures the films show the typical ferroelectric hysteresis loops. - Highlights: • (K 0.5 Na 0.5 )NbO 3 and [(K 0.5 Na 0.5 ) 0.985 La 0.005 ]NbO 3 thin films have been prepared. • The obtained thin films show an excellent (100) preferred orientation. • Doping with lanthanum results in a decrease of the leakage current density. • The dielectric properties are enhanced when doping with lanthanum

Effect of manganese doping on remnant polarization and leakage current in (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 epitaxial thin films on SrTiO3

Science.gov (United States)

Abazari, M.; Akdoǧan, E. K.; Safari, A.

2008-05-01

Single phase, epitaxial, ⟨001⟩ oriented, undoped and 1mol% Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films of 400nm thickness were synthesized on SrRuO3 coated SrTiO3. Such films exhibit well saturated hysteresis loops and have a spontaneous polarization (Ps) of 10μC /cm2, which is a 150% higher over the Ps of the undoped composition. The coercive field of 1mol% Mn doped films is 13kV/cm. Mn-doping results in three orders of magnitude decrease in leakage current above 50kV/cm electric field, which we attribute to the suppression of intrinsic p-type conductivity of undoped films by Mn donors.

Favorable ultraviolet photoelectric effects in TbMnO3/Nb-SrTiO3 heterostructures

KAUST Repository

Jin, Kexin; Zhai, Y. X.; Li, Hui; Tian, Y. F.; Luo, B. C.; Wu, Tao

2014-01-01

The rectifying properties and ultraviolet photoelectric effects in TbMnO3/Nb-doped SrTiO3 heterostructures have been investigated. The ideality factors and the diffusion voltages obtained from the current-voltage curves nonlinearly decrease

A versatile light-switchable nanorod memory: Wurtzite ZnO on perovskite SrTiO3

KAUST Repository

Kumar, Anup Bera; Peng, Haiyang; Lourembam, James; Shen, Youde; Sun, Xiaowei; Wu, Tao

2013-01-01

heterojunction memory made of wurtzite ZnO nanorods grown on perovskite Nb-doped SrTiO3 (NSTO) is reported, the electronic properties of which can be drastically reconfigured by applying a voltage and light. Despite of the distinct lattice structures of Zn

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

KAUST Repository

Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Darroudi, Taghi; Zeng, Xiaoyu; Alshareef, Husam N.; Tritt, Terry M.

2015-01-01

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

KAUST Repository

Mehdizadeh Dehkordi, Arash

2015-08-15

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Enhanced thermoelectric figure-of-merit in thermally robust, nanostructured superlattices based on SrTiO3

KAUST Repository

Abutaha, Anas I.

2015-03-24

Thermoelectric (TE) metal oxides overcome crucial disadvantages of traditional heavy-metal-alloy-based TE materials, such as toxicity, scarcity, and instability at high temperatures. Here, we report the TE properties of metal oxide superlattices, composed from alternating layers of 5% Pr3+-doped SrTiO3-δ (SPTO) and 20% Nb5+-doped SrTiO3-δ (STNO) fabricated using pulsed laser deposition (PLD). Excellent stability is established for these superlattices by maintaining the crystal structure and reproducing the TE properties after long-time (20 h) annealing at high temperature (∼1000 K). The introduction of oxygen vacancies as well as extrinsic dopants (Pr3+ and Nb5+), with different masses and ionic radii, at different lattice sites in SPTO and STNO layers, respectively, results in a substantial reduction of thermal conductivity via scattering a wider range of phonon spectrum without limiting the electrical transport and thermopower, leading to an enhancement in the figure-of-merit (ZT). The superlattice composed of 20 SPTO/STNO pairs, 8 unit cells of each layer, exhibits a ZT value of 0.46 at 1000 K, which is the highest among SrTiO3-based thermoelectrics. © 2015 American Chemical Society.

Enhanced thermoelectric figure-of-merit in thermally robust, nanostructured superlattices based on SrTiO3

KAUST Repository

Abutaha, Anas I.; Sarath Kumar, S. R.; Li, Kun; Dehkordi, Arash Mehdizadeh; Tritt, Terry M.; Alshareef, Husam N.

2015-01-01

Thermoelectric (TE) metal oxides overcome crucial disadvantages of traditional heavy-metal-alloy-based TE materials, such as toxicity, scarcity, and instability at high temperatures. Here, we report the TE properties of metal oxide superlattices, composed from alternating layers of 5% Pr3+-doped SrTiO3-δ (SPTO) and 20% Nb5+-doped SrTiO3-δ (STNO) fabricated using pulsed laser deposition (PLD). Excellent stability is established for these superlattices by maintaining the crystal structure and reproducing the TE properties after long-time (20 h) annealing at high temperature (∼1000 K). The introduction of oxygen vacancies as well as extrinsic dopants (Pr3+ and Nb5+), with different masses and ionic radii, at different lattice sites in SPTO and STNO layers, respectively, results in a substantial reduction of thermal conductivity via scattering a wider range of phonon spectrum without limiting the electrical transport and thermopower, leading to an enhancement in the figure-of-merit (ZT). The superlattice composed of 20 SPTO/STNO pairs, 8 unit cells of each layer, exhibits a ZT value of 0.46 at 1000 K, which is the highest among SrTiO3-based thermoelectrics. © 2015 American Chemical Society.

Absence of confinement in (SrTiO3)/( SrTi0.8Nb0.2O3 ) superlattices

Science.gov (United States)

Bouzerar, G.; Thébaud, S.; Bouzerar, R.; Pailhès, S.; Adessi, Ch.

2018-03-01

The reduction of dimensionality is considered an efficient pathway to boost the performances of thermoelectric materials. Quantum confinement of the carriers is expected to induce large Seebeck coefficients (S ) and it also suppresses the thermal conductivity by increasing the phonon scattering processes. However, quantum confinement in superlattices is not always easy to achieve and needs to be carefully validated. In the past decade, large values of S have been measured in (SrTiO3)/(SrTi0.8Nb0.2O3 ) superlattices [H. Ohta et al., Nat. Mater. 6, 129 (2007), 10.1038/nmat1821; Y. Mune et al., Appl. Phys. Lett. 91, 192105 (2007), 10.1063/1.2809364]. In the δ -doped compound, the reported S was almost six times larger than that of the bulk material. This huge increase has been attributed to the two-dimensional carrier confinement in the doped regions. Here, we demonstrate that the experimental data are well explained quantitatively assuming delocalized electrons in both in-plane and growth directions. Moreover, we rule out the confined electron hypothesis whose signature would be the suppression of the Seebeck coefficient. This strongly suggests that the presupposed confinement picture in these superlattices is unlikely.

Strain induced atomic structure at the Ir-doped LaAlO3/SrTiO3 interface.

Science.gov (United States)

Lee, M; Arras, R; Warot-Fonrose, B; Hungria, T; Lippmaa, M; Daimon, H; Casanove, M J

2017-11-01

The structure of Ir-doped LaAlO 3 /SrTiO 3 (001) interfaces was investigated on the atomic scale using probe-corrected transmission electron microscopy in high-angle annular dark-field scanning mode (HAADF-STEM) and electron energy loss spectroscopy (EELS), combined with first-principles calculations. We report the evolution of the strain state experimentally measured in a 5 unit-cell thick LaAlO 3 film as a function of the Ir concentration in the topmost SrTiO 3 layer. It is shown that the LaAlO 3 layers remain fully elastically strained up to 3% of Ir doping, whereas a higher doping level seems to promote strain relaxation through enhanced cationic interdiffusion. The observed differences between the energy loss near edge structure (ELNES) of Ti-L 2,3 and O-K edges at non-doped and Ir-doped interfaces are consistent with the location of the Ir dopants at the interface, up to 3% of Ir doping. These findings, supported by the results of density functional theory (DFT) calculations, provide strong evidence that the effect of dopant concentrations on the properties of this kind of interface should not be analyzed without obtaining essential information from the fine structural and chemical analysis of the grown structures.

Electrostatic analysis of n-doped SrTiO3 metal-insulator-semiconductor systems

International Nuclear Information System (INIS)

Kamerbeek, A. M.; Banerjee, T.; Hueting, R. J. E.

2015-01-01

Electron doped SrTiO 3 , a complex-oxide semiconductor, possesses novel electronic properties due to its strong temperature and electric-field dependent permittivity. Due to the high permittivity, metal/n-SrTiO 3 systems show reasonably strong rectification even when SrTiO 3 is degenerately doped. Our experiments show that the insertion of a sub nanometer layer of AlO x in between the metal and n-SrTiO 3 interface leads to a dramatic reduction of the Schottky barrier height (from around 0.90 V to 0.25 V). This reduces the interface resistivity by 4 orders of magnitude. The derived electrostatic analysis of the metal-insulator-semiconductor (n-SrTiO 3 ) system is consistent with this trend. When compared with a Si based MIS system, the change is much larger and mainly governed by the high permittivity of SrTiO 3 . The non-linear permittivity of n-SrTiO 3 leads to unconventional properties such as a temperature dependent surface potential non-existent for semiconductors with linear permittivity such as Si. This allows tuning of the interfacial band alignment, and consequently the Schottky barrier height, in a much more drastic way than in conventional semiconductors

New insights on the synthesis and electronic transport in bulk polycrystalline Pr-doped SrTiO3−δ

International Nuclear Information System (INIS)

Dehkordi, Arash Mehdizadeh; Bhattacharya, Sriparna; Darroudi, Taghi; Alshareef, Husam N.; Tritt, Terry M.

2015-01-01

Recently, we have reported a significant enhancement in the electronic and thermoelectric properties of bulk polycrystalline SrTiO 3 ceramics via praseodymium doping. This improvement was originated from the simultaneous enhancement in the thermoelectric power factor and reduction in thermal conductivity, which was contributed to the non-uniform distribution of Pr dopants. In order to further understand the underlying mechanism, we herein investigate the role of praseodymium doping source (Pr 2 O 3 versus Pr 6 O 11 ) on the synthesis and electronic transport in Pr-doped SrTiO 3 ceramics. It was observed that the high-temperature electronic transport properties are independent of the choice of praseodymium doping source for samples prepared following our synthesis strategy. Theoretical calculations were also performed in order to estimate the maximum achievable power factor and the corresponding optimal carrier concentration. The result suggests the possibility of further improvement of the power factor. This study should shed some light on the superior electronic transport in bulk polycrystalline Pr-doped SrTiO 3 ceramics and provide new insight on further improvement of the thermoelectric power factor

New insights on the synthesis and electronic transport in bulk polycrystalline Pr-doped SrTiO3−δ

KAUST Repository

Dehkordi, Arash Mehdizadeh

2015-02-07

Recently, we have reported a significant enhancement in the electronic and thermoelectric properties of bulk polycrystalline SrTiO3 ceramics via praseodymium doping. This improvement was originated from the simultaneous enhancement in the thermoelectric power factor and reduction in thermal conductivity, which was contributed to the non-uniform distribution of Pr dopants. In order to further understand the underlying mechanism, we herein investigate the role of praseodymium doping source (Pr2O3 versus Pr6O11) on the synthesis and electronic transport in Pr-doped SrTiO3 ceramics. It was observed that the high-temperature electronic transport properties are independent of the choice of praseodymium doping source for samples prepared following our synthesis strategy. Theoretical calculations were also performed in order to estimate the maximum achievable power factor and the corresponding optimal carrier concentration. The result suggests the possibility of further improvement of the power factor. This study should shed some light on the superior electronic transport in bulk polycrystalline Pr-doped SrTiO3 ceramics and provide new insight on further improvement of the thermoelectric power factor.

Spectroscopic investigations of nanostructured LiNbO3 doped with Eu3+

International Nuclear Information System (INIS)

Hreniak, D.; Speghini, A.; Bettinelli, M.; Strek, W.

2006-01-01

Structural and optical properties of the sol-gel derived nanocrystalline lithium niobate (LiNbO 3 ) powders doped with Eu 3+ ions have been studied. In particular, the influence of the sizes of nanoparticles controlled by temperature on the structural and luminescence properties has been investigated. Emission bands corresponding to 5 D emission became more resolved with increasing nanocrystal size and changed to a typical Eu 3+ :LiNbO 3 single crystal spectrum for nanocrystals having an average size of more than 40 nm. Nonlinear optical properties of nanostructured LiNbO 3 have been confirmed by simple observation of second harmonic generation effect (SHG). The possibility of using nanostructured LiNbO 3 doped with rare-earth ions as self-doubling elements in integrated optoelectronic devices has been discussed

Magnetism Control by Doping in LaAlO3/SrTiO3 Heterointerfaces.

Science.gov (United States)

Yan, Hong; Zhang, Zhaoting; Wang, Shuanhu; Wei, Xiangyang; Chen, Changle; Jin, Kexin

2018-04-25

Magnetic two-dimensional electron gases at the oxide interfaces are always one of the key issues in spintronics, giving rise to intriguing magnetotransport properties. However, reports about magnetic two-dimensional electron gases remain elusive. Here, we obtain the magnetic order of LaAlO 3 /SrTiO 3 systems by introducing magnetic dopants at the La site. The transport properties with a characteristic of metallic behavior at the interfaces are investigated. More significantly, magnetic-doped samples exhibit obvious magnetic hysteresis loops and the mobility is enhanced. Meanwhile, the photoresponsive experiments are realized by irradiating all samples with a 360 nm light. Compared to magnetism, the effects of dopants on photoresponsive and relaxation properties are negligible because the behavior originates from SrTiO 3 substrates. This work paves a way for revealing and better controlling the magnetic properties of oxide heterointerfaces.

Investigation of the electroforming and resistive switching mechanisms in Fe-doped SrTiO3 thin films

International Nuclear Information System (INIS)

Menke, Tobias

2009-01-01

To overcome the physical limits of todays memory technologies new concepts are needed. The resistive random access memory (RRAM), which bases on a nonvolatile and repeatable change of the resistance by external electrical stimuli, seems to be one promising candidate. Within the scope of this work, the model system Strontium titanate (SrTiO 3 ) has been investigated to get a deeper understanding of the underlying physical mechanism related to the resistance change. The electrical properties of SrTiO 3 (STO) can be modulated from a band insulator to metallic conduction by a self-doping with oxygen vacancies which act as shallow donors. A local accumulation or depletion of oxygen vacancies at the vicinity of the surface will lead to a local redox process which is responsible for the resistance change. To study the influence of the interfaces on the switching properties of SrTiO 3 thin films, epitaxial films of Fe-doped SrTiO 3 were grown on different bottom electrodes (SrRuO 3 , LaNiO 3 und Nb:STO) by a ''Pulsed Laser Deposition'' technique. An atomic force microscope equipped with a conductive tip (LC-AFM) allowed studying the conductivity of the deposited films on the nanometer scale. Resistive switching of lateral structures smaller than ∝5 nm could be realized which represents the potential of this material for a further downscaling of RRAM devices. The deposition of top electrodes, made of Platinum or Titanium, allowed the electrical characterization of metal-insulator-metal (MIM) structures. An extensive investigation of pristine MIM-devices by impedance spectroscopy showed the big impact of the metal-insulator interface on the overall device resistance. Furthermore, a chemical polarization was studied by dynamical current sweeps and identified as a volatile resistance variation. Usually a forming procedure is needed to ''enable'' the resistive switching properties in MIM devices. The electroforming of these devices was extensively studied and could be

Electronic structure and visible light photocatalysis water splitting property of chromium-doped SrTiO3

International Nuclear Information System (INIS)

Liu, J.W.; Chen, G.; Li, Z.H.; Zhang, Z.G.

2006-01-01

Cr-doped SrTi 1- x Cr x O 3 (x=0.00, 0.02, 0.05, 0.10) powders, prepared by solvothermal method, were further characterized by ultraviolet-visible (UV-vis) absorption spectroscopy. The UV-vis spectra indicate that the SrTi 1- x Cr x O 3 powders can absorb not only UV light like pure SrTiO 3 powder but also the visible-light spectrum (λ>420 nm). The results of density functional theory (DFT) calculation illuminate that the visible-light absorption bands in the SrTi 1- x Cr x O 3 catalyst are attributed to the band transition from the Cr 3d to the Cr 3d+Ti 3d hybrid orbital. The photocatalytic activities of chromium-doped SrTiO 3 both under UV and visible light are increased with the increase in the amounts of chromium. -- Graphical abstract: SrTi 1- x Cr x O 3 powders, prepared by solvothermal method, can absorb not only UV light like pure SrTiO 3 powder but also the visible-light spectrum (λ>420 nm). The results of DFT calculation illuminate that the visible-light absorption bands in the SrTi 1- x Cr x O 3 catalyst are attributed to the band transition from the Cr 3d to the Cr 3d+Ti 3d hybrid orbital

Two-dimensional thermoelectric Seebeck coefficient of SrTiO3-based superlattices

International Nuclear Information System (INIS)

Ohta, Hiromichi

2008-01-01

This review provides the origin of the unusually large thermoelectric Seebeck coefficient vertical stroke S vertical stroke of a two-dimensional electron gas confined within a unit cell layer thickness (∝0.4 nm) of a SrTi 0.8 Nb 0.2 O 3 layer of artificial superlattices of SrTiO 3 /SrTi 0.8 Nb 0.2 O 3 [H. Ohta et al., Nature Mater. 6, 129 (2007)]. The vertical stroke S vertical stroke 2D values of the[(SrTiO 3 ) 17 /(SrTi 0.8 Nb 0.2 O 3 ) y ] 20 superlattice increase proportional to y -0.5 , and reach 290 μV K -1 (y=1) at room temperature, which is ∝5 times larger than that of the SrTi 0.8 Nb 0.2 O 3 bulk (vertical stroke S vertical stroke 3D =61 μVK -1 ), proving that the density of states in the ground state for SrTiO 3 increases in inverse proportion to y. The critical barrier thickness for quantum electron confinement is also clarified to be 6.25 nm (16 unit cells of SrTiO 3 ). Significant structural changes are not observed in the superlattice after annealing at 900 K in a vacuum. The value of vertical stroke S vertical stroke 2D of the superlattice gradually increases with temperature and reaches 450 μVK -1 at 900 K, which is ∝3 times larger than that of bulk SrTi 0.8 Nb 0.2 O 3 . These observations provide clear evidence that the [(SrTiO 3 ) 17 /(SrTi 0.8 Nb 0.2 O 3 ) 1 ] 20 superlattice is stable and exhibits a giant vertical stroke S vertical stroke even at high temperature. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

New insights on the synthesis and electronic transport in bulk polycrystalline Pr-doped SrTiO3−δ

KAUST Repository

Dehkordi, Arash Mehdizadeh; Bhattacharya, Sriparna; Darroudi, Taghi; Alshareef, Husam N.; Tritt, Terry M.

2015-01-01

versus Pr6O11) on the synthesis and electronic transport in Pr-doped SrTiO3 ceramics. It was observed that the high-temperature electronic transport properties are independent of the choice of praseodymium doping source for samples prepared following our

Analysis of SrTiO sub 3 step-flow growth by using RHEED

CERN Document Server

Nakagawa, N; Kawasaki, M; Ohashi, S; Koinuma, H

1999-01-01

SrTiO sub 3 homoepitaxial films were deposited by pulsed-laser deposition in a chamber equipped with a reflection high-energy electron-diffraction (RHEED) specular spot-intensity monitoring system. Changes in the substrate temperature or the excimer laser pulse rate gave rise to different behaviors of the RHEED specular intensity. At low temperatures and high pulse rates, ordinary RHEED oscillations were observed, indicating layer-by-layer growth. At very high temperatures and low pulse rates, the RHEED specular intensity was modulated synchronously with the excimer laser pulses, indicating that film growth proceeded in the step-flow mode. No Nb diffusion from the substrates into the homoepitaxial films was observed, even at the highest deposition temperatures, when Nb-doped STO substrates were used.

Integrated oxygen sensors based on Mg-doped SrTiO3 fabricated by screen-printing

DEFF Research Database (Denmark)

Zheng, H.; Toft Sørensen, O.

1998-01-01

This paper describes the fabrication and testing of Mg-doped SrTiO3 thick-film oxygen sensors with an integrated Pt heater. The results show that the sensor exhibits a PO2 dependence according to R proportional to PO2-1/4 in the considered PO2 range(2.5 x 10(-5) bar

SrTiO3 Nanocube-Doped Polyaniline Nanocomposites with Enhanced Photocatalytic Degradation of Methylene Blue under Visible Light

Directory of Open Access Journals (Sweden)

Syed Shahabuddin

2016-02-01

Full Text Available The present study highlights the facile synthesis of polyaniline (PANI-based nanocomposites doped with SrTiO3 nanocubes synthesized via the in situ oxidative polymerization technique using ammonium persulfate (APS as an oxidant in acidic medium for the photocatalytic degradation of methylene blue dye. Field emission scanning electron microscopy (FESEM, transmission electron microscopy (TEM, thermogravimetric analysis (TGA, X-ray diffraction (XRD, UV–Vis spectroscopy, Brunauer–Emmett–Teller analysis (BET and Fourier transform infrared spectroscopy (FTIR measurements were used to characterize the prepared nanocomposite photocatalysts. The photocatalytic efficiencies of the photocatalysts were examined by degrading methylene blue (MB under visible light irradiation. The results showed that the degradation efficiency of the composite photocatalysts that were doped with SrTiO3 nanocubes was higher than that of the undoped polyaniline. In this study, the effects of the weight ratio of polyaniline to SrTiO3 on the photocatalytic activities were investigated. The results revealed that the nanocomposite P-Sr500 was found to be an optimum photocatalyst, with a 97% degradation efficiency after 90 min of irradiation under solar light.

Integrated oxygen sensors based on Mg-doped SrTiO3 fabricated by screen-printing

DEFF Research Database (Denmark)

Zheng, H.; Sørensen, Ole Toft

2000-01-01

This paper describes the fabrication and testing of Mg-doped SrTiO3 thick-film oxygen sensors with an integrated Pt heater. The results show that the sensor exhibits a P-o2 dependence according to R proportional to p(o2)(-1/4) in the considered P-o2 range(2.5 x 10(-5) bar

Strong Energy-momentum Dispersion of Phonon Dressed Carriers in the Lightly Doped Band Insulator SrTiO3

International Nuclear Information System (INIS)

Meevasana, Warawat

2010-01-01

Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates. As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO 3 (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La 2 CuO 4 by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO 3 . Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a λ(prime) ∼ 0.3 and an overall bandwidth renormalization suggesting an overall λ(prime) ∼ 0.7 coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.

Regulation of depletion layer width in Pb(Zr,Ti)O3/Nb:SrTiO3 heterostructures

Science.gov (United States)

Bai, Yu; Jie Wang, Zhan; Cui, Jian Zhong; Zhang, Zhi Dong

2018-05-01

Improving the tunability of depletion layer width (DLW) in ferroelectric/semiconductor heterostructures is important for the performance of some devices. In this work, 200-nm-thick Pb(Zr0.4Ti0.6)O3 (PZT) films were deposited on different Nb-doped SrTiO3 (NSTO) substrates, and the tunability of DLW at PZT/NSTO interfaces were studied. Our results showed that the maximum tunability of the DLW was achieved at the NSTO substrate with 0.5 wt% Nb. On the basis of the modified capacitance model and the ferroelectric semiconductor theory, we suggest that the tunability of the DLW in PZT/NSTO heterostructures can be attributed to a delicate balance of the depletion layer charge and the ferroelectric polarization charge. Therefore, the performance of some devices related to the tunability of DLW in ferroelectric/semiconductor heterostructures can be improved by modulating the doping concentration in semiconducting electrode materials.

Raman and NMR study in MgO-doped LiNbO3 crystal

International Nuclear Information System (INIS)

Hu, L.J.; Chang, Y.H.; Chang, C.S.; Yang, S.J.; Hu, M.L.; Tse, W.S.

1991-01-01

This paper reports on the MgO-doped LiNbO 3 crystal grown and studied by NMR and Raman techniques. The solubility of MgO in the LiNbO 3 crystal is as much as 30 mole %. It is shown in NMR spectra that the number of Nb 5+ cations at A-site (Li-site) decrease as Mg concentration increased when the Mg content is lower than 5 mole %. The vibration of (NbO 6 ) octahedron and translations involving Li + and Mg 2+ cations motion can be identified by replacing Nb 5+ and Li + cations with Ta 5+ and Mg 2+ cations through Raman spectra. The 115 cm -1 and 151 cm -1 peaks are due to the translational modes of Mg 2+ and Li + cations. The doping mechanisms of MgO are proposed

Bottom-up synthesis of up-converting submicron-sized Er3+-doped LiNbO3 particles

International Nuclear Information System (INIS)

Jardiel, T.; Caballero, A.C.; Marín-Dobrincic, M.; Cantelar, E.; Cussó, F.

2012-01-01

A new and simple wet chemical synthesis method is proposed to prepare submicron-sized Erbium-doped LiNbO 3 powders. The synthesis procedure comprises the co-precipitation of lithium and erbium ions from common precursors and their subsequent reaction with niobium ethoxide. A systematic characterization by means of X-Ray Diffraction (XRD), X-ray Fluorescence (XRF), Inductively Coupled Plasma (ICP-OES), Atomic Absorption (AAS), Field Emission Scanning Electron Microscopy (FE-SEM), as well as by the examination of the luminescence properties, evidence that with this method a congruent Er 3+ -doped LiNbO 3 single phase material can be obtained without using complex and time-consuming processing steps. The synthesized powders exhibit efficient IR to VIS up-conversion emissions under 974 nm pumping. -- Highlights: ► A novel chemical route to the preparation of LiNbO 3 powders has been developed. ► This process avoids complex and time-consuming processing steps. ► A congruent Er 3+ -doped LiNbO 3 single phase material can be obtained by this way. ► The luminescence properties are the expected for this composition.

Microwave-Hydrothermal Synthesis and Characterization of High-Purity Nb Doped BaTiO3 Nanocrystals

Directory of Open Access Journals (Sweden)

A. Khanfekr

2014-01-01

Full Text Available The synthesis of Nb doped BaTiO3 has been investigated under Microwave-Hydrothermal (MH conditions in the temperature of 150°C for only 2 h using C16H36O4Ti, BaH2O2.8H2O and NbCl5 as Ba, Ti and  Nb sources, respectively.  Typical experiments performed on MH processing have not yet reported for Nb doped BaTiO3.  In the MH process, the formation of high purity nano tetragonal Nb-BaTiO3 was strongly enhanced. New hydrothermal method was used instead of the previous solid state reaction for the BaTiO3±Nb2O3 system. The new method uses high pressure to create nano dimension particles in a lower time and temperature. In case of the phase evolution studies, the XRD pattern measurements and Raman spectroscopy were performed. TEM and FE-SEM images were taken for the detailed analysis of the particle size, surface and morphology.  Synthesis of Nb doped BaTiO3 with the Microwave-hydrothermal provides an advantage of fast crystallization and reduced crystal size when compared to existing methods.

Photoluminescent properties of Pr3+ doped YTiAO6 (A= Nb&Ta) euxenite compounds

Science.gov (United States)

Venugopal, Meenu; Kumar, H. Padma

2018-04-01

Pr3+ doped YTiAO6 (A = Nb and Ta) compounds were prepared by conventional solid state ceramic route. X - ray diffraction studies of the samples confirmed the euxenite orthorhombic phase formation. Effect of Pr3+ doping on the optical and luminescence properties of YTiAO6 (A = Nb and Ta) were studied. The strong absorption in the UV region are due to the absorption by the host YTiAO6 (A = Nb and Ta) and all other peaks can be attributed to that of Pr3+. Host emission peaks are observed around 485 nm and 460 nm in all samples. The red emission observed at 614 nm in the doped samples corresponds to the 1D2 to 3H4 transition of Pr3+ ion. CIE colour coordinates and chromaticity values were also discussed.

Photoluminescence of rare-earth ion (Eu3+, Tm3+, and Er3+)-doped and co-doped ZnNb2O6 for solar cells

Science.gov (United States)

Gao, Sen-Pei; Qian, Yan-Nan; Wang, Biao

2015-08-01

Visible converted emissions produced at an excitation of 286 nm in ZnNb2O6 ceramics doped with rare-earth ions (RE = Eu3+, Tm3+, Er3+ or a combination of these ions) were investigated with the aim of increasing the photovoltaic efficiency of solar cells. The structure of RE:ZnNb2O6 ceramics was confirmed by x-ray diffraction patterns. The undoped ZnNb2O6 could emit a blue emission under 286-nm excitation, which is attributed to the self-trapped excitons’ recombination of the efficient luminescence centers of edge-shared NbO6 groups. Upon 286-nm excitation, Eu:ZnNb2O6, Tm:ZnNb2O6, and Er:ZnNb2O6 ceramics showed blue, green, and red emissions, which correspond to the transitions of 5D0 → 7FJ (J = 1-4) (Eu3+), 1G4 → 3H6 (Tm3+), and 2H11/2/4S3/2 → 4I15/2 (Er3+), respectively. The calculated CIE chromaticity coordinates of Eu:ZnNb2O6, Tm:ZnNb2O6, and Er:ZnNb2O6 are (0.50, 0.31), (0.14, 0.19), and (0.29, 0.56), respectively. RE ion-co-doped ZnNb2O6 showed a combination of characteristic emissions. The chromaticity coordinates of Eu/Tm:ZnNb2O6, Eu/Er:ZnNb2O6, and Tm/Er:ZnNb2O6 were calculated to be (0.29, 0.24), (0.45, 0.37), and (0.17, 0.25). Project supported by the National Natural Science Foundation of China (Grant Nos. 10572155 and 10732100) and the Research Fund for the Doctoral Program of Ministry of Education, China (Grant No. 20130171130003).

XPS Analysis of Ni and Oxygen in Single-Sintered SrTiO3 Multifunction Ceramic

Institute of Scientific and Technical Information of China (English)

无

2001-01-01

XPS analyses have been performed to investigate the chemical conditions of Ni and oxygen on grain surfaces in single-sintered SrTiO3 capacitor-varistor ceramic doped with Nb2O5 and NiO. It is ascertained that Ni is in form of Ni2+ ions, which substitute for Ti4+ ions on grain surfaces during the oxidizing annealing. Moreover, it is confirmed that three kinds of chemically adsorbed oxygen such as O2-, O- and O~ are formed on grain surfaces. It is proposed that these behaviors contribute greatly to the generation of multiple types of grain boundary acceptor states in the ceramic.

Ferroelectricity of Sn-doped SrTiO3 perovskites with tin at both A and B sites

Science.gov (United States)

Suzuki, Shoichiro; Honda, Atsushi; Iwaji, Naoki; Higai, Shin'ichi; Ando, Akira; Takagi, Hiroshi; Kasatani, Hirofumi; Deguchi, Kiyoshi

2012-08-01

We successfully obtained Sn-doped SrTiO3 (SSTO) perovskites, and clarified their ferroelectricity and structural properties by using first-principles theoretical calculations. The ferroelectricity of SSTO was confirmed by the appearance of a dielectric permittivity maximum and a clear hysteresis loop of the relationship between the external electric field and the electric flux density below 180 K. X-ray diffraction and Raman spectra revealed the structural phase transition of SSTO at approximately 200 K. We directly observed by spherical aberration corrected scanning transmission electron microscopy with energy-dispersive x-ray spectroscopy that Sn ions are doped into both Sr and Ti sites (SnA and SnB), and that SnA is located at an off-centered position. We also performed theoretical analyses of SSTO and related perovskites, and found that SnA is preferentially located in an off-centered position and that SnA and the O6 octahedron, which includes SnB in its center, oscillate along the antiphase direction in the soft mode. Thus, we propose that the ferroelectricity of SSTO originates from the antiphase off-centering, which induces ferroelectric nanoregions in paraelectric SrTiO3.

Cr3+ and Nb5+ co-doped Ti2Nb10O29 materials for high-performance lithium-ion storage

Science.gov (United States)

Yang, Chao; Yu, Shu; Ma, Yu; Lin, Chunfu; Xu, Zhihao; Zhao, Hua; Wu, Shunqing; Zheng, Peng; Zhu, Zi-Zhong; Li, Jianbao; Wang, Ning

2017-08-01

Ti2Nb10O29 is an advanced anode material for lithium-ion batteries due to its large specific capacity and high safety. However, its poor electronic/ionic conductivity significantly limits its rate capability. To tackle this issue, a Cr3+-Nb5+ co-doping is employed, and a series of CrxTi2-2xNb10+xO29 compounds are prepared. The co-doping does not change the Wadsley-Roth shear structure but increases the unit-cell volume and decreases the particle size. Due to the increased unit-cell volumes, the co-doped samples show increased Li+-ion diffusion coefficients. Experimental data and first-principle calculations reveal significantly increased electronic conductivities arising from the formation of impurity bands after the co-doping. The improvements of the electronic/ionic conductivities and the smaller particle sizes in the co-doped samples significantly contribute to improving their electrochemical properties. During the first cycle at 0.1 C, the optimized Cr0.6Ti0.8Nb10.6O29 sample delivers a large reversible capacity of 322 mAh g-1 with a large first-cycle Coulombic efficiency of 94.7%. At 10 C, it retains a large capacity of 206 mAh g-1, while that of Ti2Nb10O29 is only 80 mAh g-1. Furthermore, Cr0.6Ti0.8Nb10.6O29 shows high cyclic stability as demonstrated in over 500 cycles at 10 C with tiny capacity loss of only 0.01% per cycle.

Leakage current behavior in lead-free ferroelectric (K,Na)NbO3-LiTaO3-LiSbO3 thin films

Science.gov (United States)

Abazari, M.; Safari, A.

2010-12-01

Conduction mechanisms in epitaxial (001)-oriented pure and 1 mol % Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.1,Sb0.06)O3 (KNN-LT-LS) thin films on SrTiO3 substrate were investigated. Temperature dependence of leakage current density was measured as a function of applied electric field in the range of 200-380 K. It was shown that the different transport mechanisms dominate in pure and Mn-doped thin films. In pure (KNN-LT-LS) thin films, Poole-Frenkel emission was found to be responsible for the leakage, while Schottky emission was the dominant mechanism in Mn-doped thin films at higher electric fields. This is a remarkable yet clear indication of effect of 1 mol % Mn on the resistive behavior of such thin films.

Significant enhancement in thermoelectric properties of polycrystalline Pr-doped SrTiO3−δ ceramics originating from nonuniform distribution of Pr dopants

KAUST Repository

Dehkordi, Arash Mehdizadeh

2014-05-12

Recently, we have reported a significant enhancement ( >70% at 500 °C) in the thermoelectric power factor (PF) of bulk polycrystalline Pr-doped SrTiO3 ceramics employing a novel synthesis strategy which led to the highest ever reported values of PF among doped polycrystalline SrTiO3. It was found that the formation of Pr-rich grain boundary regions gives rise to an enhancement in carrier mobility. In this Letter, we investigate the electronic and thermal transport in Sr1− x Pr x TiO3 ceramics in order to determine the optimum doping concentration and to evaluate the overall thermoelectric performance. Simultaneous enhancement in the thermoelectric power factor and reduction in thermal conductivity in these samples resulted in more than 30% improvement in the dimensionless thermoelectric figure of merit (ZT) for the whole temperature range over all previously reported maximum values. Maximum ZT value of 0.35 was obtained at 500 °C.

Significant enhancement in thermoelectric properties of polycrystalline Pr-doped SrTiO3−δ ceramics originating from nonuniform distribution of Pr dopants

KAUST Repository

Dehkordi, Arash Mehdizadeh; Bhattacharya, Sriparna; He, Jian; Alshareef, Husam N.; Tritt, Terry M.

2014-01-01

Recently, we have reported a significant enhancement ( >70% at 500 °C) in the thermoelectric power factor (PF) of bulk polycrystalline Pr-doped SrTiO3 ceramics employing a novel synthesis strategy which led to the highest ever reported values of PF among doped polycrystalline SrTiO3. It was found that the formation of Pr-rich grain boundary regions gives rise to an enhancement in carrier mobility. In this Letter, we investigate the electronic and thermal transport in Sr1− x Pr x TiO3 ceramics in order to determine the optimum doping concentration and to evaluate the overall thermoelectric performance. Simultaneous enhancement in the thermoelectric power factor and reduction in thermal conductivity in these samples resulted in more than 30% improvement in the dimensionless thermoelectric figure of merit (ZT) for the whole temperature range over all previously reported maximum values. Maximum ZT value of 0.35 was obtained at 500 °C.

Enhanced photorefractive properties in Hf, Ce and Cu co-doped LiNbO{sub 3} crystals for holographic application

Energy Technology Data Exchange (ETDEWEB)

Zhang, Tao, E-mail: tzhang_hit02@yahoo.com [Key Laboratory of In-fiber Integrated Optics, Ministry of Education of China, Harbin Engineering University, Harbin 150001 (China); College of Science, Harbin Engineering University, Harbin 150001 (China); Postdoctoral Research Station of Mechanical Engineering, College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001 (China); Wang, Xin; Geng, Tao; Tong, Chengguo [Key Laboratory of In-fiber Integrated Optics, Ministry of Education of China, Harbin Engineering University, Harbin 150001 (China); College of Science, Harbin Engineering University, Harbin 150001 (China); Kang, Chong [Key Laboratory of In-fiber Integrated Optics, Ministry of Education of China, Harbin Engineering University, Harbin 150001 (China); College of Science, Harbin Engineering University, Harbin 150001 (China); Postdoctoral Research Station of Mechanical Engineering, College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001 (China)

2015-04-25

Graphical abstract: Correlation spots of 200 holograms in a Hf, Ce and Cu co-doped LiNbO{sub 3}. - Highlights: • Several doped LiNbO{sub 3} crystals with various level of Hf doping were grown by Cz method. • IR peak shift is attributed to the complex defect change at different level of Hf. • Enhanced photorefractive properties have been got with higher Hf-doping level. • Reduced defect and increased photoconductivity are responsible for optical properties. • 200 holograms’ experiment is realized in a coherent volume 0.073 cm{sup 3}. - Abstract: Hf, Ce and Cu co-doped LiNbO{sub 3} crystals with various level of Hf doping were grown in air by a conventional Cz method. The infrared spectra were measured to discuss the defect structures and the mechanism of the absorption peak shift in these crystals. The light-induced scattering of the crystals was evaluated by the transmitted light method. The influence of the Hf-doping level on the photorefractive properties of Hf, Ce and Cu co-doped LiNbO{sub 3} crystals was studied via two-beam coupling. It is found that proper doping Hf is an efficient method to enhance the comprehensive photorefractive properties of the LiNbO{sub 3}. Using one of these crystals as medium, 200 holograms storage and correlation experiments based on angle fractal multiplexing have been realized in a coherent volume 0.073 cm{sup 3}. Moreover the diffraction efficiency is uniform and the storage density has reached 2.2 Gb/cm{sup 3}.

Favorable ultraviolet photoelectric effects in TbMnO3/Nb-SrTiO3 heterostructures

KAUST Repository

Jin, Kexin

2014-12-01

The rectifying properties and ultraviolet photoelectric effects in TbMnO3/Nb-doped SrTiO3 heterostructures have been investigated. The ideality factors and the diffusion voltages obtained from the current-voltage curves nonlinearly decrease with increasing the temperature. It is observed that the maximum photovoltaic values of the heterostructure irradiated by the 365 nm (2.6 mW/mm2) and 248 nm (0.71 mJ/mm2) lights are about 0.121 V and 0.119 V at T=300 K, respectively. The relations between the relaxation of photovoltages after the irradiation and the power intensity are revealed. These results suggest the potential applications in the development of ultraviolet detectors using oxides-based heterostructures.

Electronic Structure and Band Alignment at the NiO and SrTiO ₃ p–n Heterojunctions

Energy Technology Data Exchange (ETDEWEB)

Zhang, Kelvin H. L. [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Wu, Rui [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Tang, Fengzai [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Li, Weiwei [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Oropeza, Freddy E. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.; Qiao, Liang [School of Materials, The University of Manchester, Manchester M13 9PL, U.K.; Lazarov, Vlado K. [Department of Physics, University of York, Heslington, York YO10 5DD, U.K.; Du, Yingge [Physical Sciences Division, Physical & amp, Computational; Payne, David J. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.; MacManus-Driscoll, Judith L. [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Blamire, Mark G. [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.

2017-07-25

Understanding the energetics at the interface including the alignment of valence and conduction bands, built-in potentials, and ionic and electronic reconstructions, is an important challenge in designing oxide interfaces that have controllable multi-functionalities for novel (opto-)electronic devices. In this work, we report detailed investigations on the hetero-interface of wide bandgap p-type NiO and n-type SrTiO3 (STO). We show that despite a large lattice mismatch (~7%) and dissimilar crystal structure, high-quality NiO and Li doped NiO (LNO) thin films can be epitaxially grown on STO(001) substrates through a domain matching epitaxy (DME) mechanism. X-ray photoelectron spectroscopy (XPS) studies indicate that NiO/STO heterojunctions form a type II “staggered” band alignment. In addition, a large built-in potential of up to 0.97 eV was observed at the interface of LNO and Nb doped STO (NbSTO). The LNO/NbSTO p-n heterojunctions exhibit a large rectification ratio of 2×103, but also a large ideality factor of 4.3. The NiO/STO p-n heterojunctions have important implication for applications in photocatalysis and photodetector as the interface provides favourable energetics for facile separation and transport of photogenerated electrons and holes.

Spectral evolution of Eu{sup 3+} doped Y{sub 3}NbO{sub 7} niobate induced by temperature

Energy Technology Data Exchange (ETDEWEB)

Kim, K-Y.; Durand, A. [CNRS, ICMCB, UPR 9048, F-33600 Pessac (France); Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac (France); Heintz, J-M.; Veillere, A. [CNRS, ICMCB, UPR 9048, F-33600 Pessac (France); Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac (France); Bordeaux INP, ICMCB, UPR 9048, F-33600 Pessac (France); Jubera, V., E-mail: veronique.jubera@u-bordeaux.fr [CNRS, ICMCB, UPR 9048, F-33600 Pessac (France); Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac (France)

2016-03-15

A Eu{sup 3+} doped Y{sub 3}NbO{sub 7} niobate powder was synthetized using a polymerizable complex route. It gave rise to nanometric particles that crystallized in the fluorine structure, corresponding to the Y{sub 3}NbO{sub 7} phase. The thermal evolution of this powder was followed up to 1600 °C, using X-ray diffraction and optical characterizations. The fluorine structure was maintained in the whole temperature range. However, spectral evolution of the samples calcined above 900 °C showed a more complex situation. Emission spectra of powders heat treated at different temperatures showed an evolution of the emission lines that can be attributed first to a better crystallization of the niobate phase and second to its partial decomposition in favor of the formation of YNbO{sub 4} and Y{sub 2}O{sub 3}. Although the Y{sub 3}NbO{sub 7} phase appeared stable up to 1650 °C, from X-ray diffraction analysis, spectral analysis showed that the local environment of the doping element is modified from 1100 °C. - Graphical abstract: Spectral evolution of Eu{sup 3+} doped Y{sub 3}NbO{sub 7} niobate induced by temperature.

Bottom-up synthesis of up-converting submicron-sized Er{sup 3+}-doped LiNbO{sub 3} particles

Energy Technology Data Exchange (ETDEWEB)

Jardiel, T., E-mail: jardiel@icv.csic.es [Departamento de Electroceramica, Instituto de Ceramica y Vidrio-CSIC, Kelsen 5, 28049 Madrid (Spain); Caballero, A.C. [Departamento de Electroceramica, Instituto de Ceramica y Vidrio-CSIC, Kelsen 5, 28049 Madrid (Spain); Marin-Dobrincic, M.; Cantelar, E.; Cusso, F. [Departamento de Fisica de Materiales, C-04, Facultad de Ciencias, Universidad Autonoma de Madrid, Avda. Francisco Tomas y Valiente 7, 28049 Madrid (Spain)

2012-08-15

A new and simple wet chemical synthesis method is proposed to prepare submicron-sized Erbium-doped LiNbO{sub 3} powders. The synthesis procedure comprises the co-precipitation of lithium and erbium ions from common precursors and their subsequent reaction with niobium ethoxide. A systematic characterization by means of X-Ray Diffraction (XRD), X-ray Fluorescence (XRF), Inductively Coupled Plasma (ICP-OES), Atomic Absorption (AAS), Field Emission Scanning Electron Microscopy (FE-SEM), as well as by the examination of the luminescence properties, evidence that with this method a congruent Er{sup 3+}-doped LiNbO{sub 3} single phase material can be obtained without using complex and time-consuming processing steps. The synthesized powders exhibit efficient IR to VIS up-conversion emissions under 974 nm pumping. -- Highlights: Black-Right-Pointing-Pointer A novel chemical route to the preparation of LiNbO{sub 3} powders has been developed. Black-Right-Pointing-Pointer This process avoids complex and time-consuming processing steps. Black-Right-Pointing-Pointer A congruent Er{sup 3+}-doped LiNbO{sub 3} single phase material can be obtained by this way. Black-Right-Pointing-Pointer The luminescence properties are the expected for this composition.

Explanation for the temperature dependence of plasma frequencies in SrTiO3 using mixed-polaron theory

International Nuclear Information System (INIS)

Eagles, D.M.; Georgiev, M.; Petrova, P.C.

1996-01-01

A theory of mixed polarons is used to interpret the published experimental results of Gervais et al. on temperature-dependent plasma frequencies in Nb-doped SrTiO 3 . For given polaron masses before mixing, the appropriate average mixed-polaron mass at any temperature T depends on two quantities, δ and b, which are measures of the separation between the bottoms of large and nearly small polaron bands before mixing and of a mixing matrix element; δ and b are assumed to have arbitrary linear dependences on T, probably related to a T dependence of the bare mass, and a term quadratic in T is included in δ, determined from the T dependence of large-polaron binding energies. Including a constraint on the ratio δ/|b| at low T from known masses from specific-heat data, satisfactory agreement is obtained with masses determined from plasma frequencies. This gives further support for the theory of mixed polarons in SrTiO 3 in addition to that already published. copyright 1996 The American Physical Society

Fabrication of Schottky Junction Between Au and SrTiO3

Science.gov (United States)

Inoue, Akira; Izumisawa, Kei; Uwe, Hiromoto

2001-05-01

A Schottky junction with a high rectification ratio between Au and La-doped SrTiO3 has been fabricated using a simple surface treatment. Highly La-doped (5%) SrTiO3 single crystals are annealed in O2 atmosphere at about 1000°C for 1 h and etched in HNO3 for more than five min. The HNO3 etching is performed in a globe box containing N2 to prevent pollution from the air. After the treatment, Au is deposited on the SrTiO3 surface in a vacuum (˜ 10-7 Torr) with an e-gun evaporator. The current voltage characteristics of the junction have shown excellent rectification properties, although junctions using neither annealed nor etched SrTiO3 exhibit high leak current in reverse voltage. The rectification ratio of the junction at 1 V is more than six orders of magnitude and there is no hysteresis in the current voltage spectra. The logarithm of the current is linear with the forward bias voltage. The ideal factor of the junction is estimated to be about 1.68. These results suggest that, if prevented from being pollution by the air, a good Schottky junction can be obtained by easy processes such as annealing in oxygen atmosphere and surface etching with acid.

Thickness and Nb-doping effects on ferro- and piezoelectric properties of highly a-axis-oriented Nb-doped Pb(Zr0.3Ti0.7)O3 films

Science.gov (United States)

Zhu, Zhi-Xiang; Ruangchalermwong, C.; Li, Jing-Feng

2008-09-01

Tetragonal Nb-doped Pb(Zr0.3Ti0.7)O3 (PNZT) films with a lead oxide seeding layer were deposited on the Pt(111)/Ti/SiO2/Si(100) substrates by sol-gel processing. The as-grown PNZT films with thicknesses ranging from about 0.08 to 0.78 μm show highly a-axis preferential orientation, and their ferroelectric and piezoelectric properties improved with increasing film thickness. Due to the combined effects of Nb doping and a-axis texturing as well as reduced substrate constraint, a high d33 constant up to 196 pm/V was obtained for PNZT film at 0.78 μm in addition to a large remnant polarization of 69 μC/cm2. This well a-axis-oriented PNZT films on platinized Si with a high piezoresponse are suitable for the fabrication of microelectromechanical devices.

Rotational Symmetry Breaking in a Trigonal Superconductor Nb-doped Bi_{2}Se_{3}

Directory of Open Access Journals (Sweden)

Tomoya Asaba

2017-01-01

Full Text Available The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi_{2}Se_{3} is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb-doped Bi_{2}Se_{3}. As a result, the in-plane magnetic torque signal vanishes every 60°. More importantly, the superconducting hysteresis loop amplitude is enhanced along one preferred direction, spontaneously breaking the rotational symmetry. This observation indicates the presence of nematic order in the superconducting ground state of Nb-doped Bi_{2}Se_{3}.

Neutron and X-ray study of stoichiometric and doped LiNbO3:Zn0.08

International Nuclear Information System (INIS)

Sulyanov, S.; Maximov, B.; Volk, T.; Boysen, H.; Schneider, J.; Rubinina, N.; Hansen, Th.

2002-01-01

LiNbO 3 (LN) crystals possess useful optical properties, which are strongly dependent on both the crystal stoichiometry and the content of dopants such as Mg 2+ , Zn 2+ , In 3+ , and Sc 3+ . Such elements drastically reduce photorefraction at a sufficiently high threshold concentration, which for Zn is in the range of 7-8 at. % and was supposed to be connected with the change of dopant-atom localisation in the lattice. We report the results of a single-crystal neutron study of stoichiometric, congruent, and doped (with 8.2 at. % Zn) LiNbO 3 at T=78 K and 298 K and also a multi-pattern powder neutron and X-ray Rietveld refinement of the doped material. Zn ions occupy both Li and Nb sites and there is no residual Nb on Li sites. LN single crystals are very perfect, and extinction problems are discussed. (orig.)

Correlation of infrared spectra and phase transitions in annealed proton-exchanged MgO doped LiNbO3

International Nuclear Information System (INIS)

Sun, Jian; Xu, Chang-qing

2015-01-01

Infrared spectra of OH − groups in annealed proton-exchanged (APE) 5 mol. % MgO-doped LiNbO 3 (MgO:LiNbO 3 ) crystals were studied using the Fourier transform infrared spectroscopy technique. Samples were prepared by benzoic acid proton-exchange followed with thermal annealing in oxygen. Evolutions of absorption peaks in APE MgO:LiNbO 3 crystals were recorded and analyzed. Comparing with none-doped APE LiNbO 3 crystals, a different phase transition behavior was found during thermal annealing. A periodically poled MgO:LiNbO 3 slab waveguide was prepared using identical procedures, and the second harmonic generation (SHG) signals were measured. Comparing the obtained SHG results with the infrared spectra, relationships between the phase transitions and the recovery of second-order nonlinear coefficients during thermal annealing were investigated. Finally, a method for optimizing the performance of MgO:LiNbO 3 waveguides was proposed

Structural investigation and luminescence of nanocrystalline lanthanide doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Pin, Sonia [Paul Scherrer Institute, General Energy Research (ENE), Laboratory for Bioenergy and Catalysis, CH-5232 Villigen PSI (Switzerland); Piccinelli, Fabio [Dipartimento di Biotecnologie, Universita di Verona and INSTM, UdR Verona, Strada Le Grazie 15, I-37134 Verona (Italy); Upendra Kumar, Kagola [Grupo de Fotonica e Fluidos Complexos, Instituto de Fisica, Universidade Federal de Alagoas (UFAL), Maceio-AL (Brazil); Enzo, Stefano [Dipartimento di Chimica, Universita di Sassari, 07100 Sassari (Italy); Ghigna, Paolo [Dipartimento di Chimica, Universita di Pavia, V.le Taramelli 16, I-27100 Pavia (Italy); Cannas, Carla; Musinu, Anna [Dipartimento di Scienze Chimiche, Universita di Cagliari, Cittadella Universitaria Monserrato, I-09042 Cagliari (Italy); Mariotto, Gino [Dipartimento di Informatica, Universita di Verona, Strada Le Grazie 15, I-37134 Verona (Italy); Bettinelli, Marco [Dipartimento di Biotecnologie, Universita di Verona and INSTM, UdR Verona, Strada Le Grazie 15, I-37134 Verona (Italy); Speghini, Adolfo, E-mail: adolfo.speghini@univr.it [Dipartimento di Biotecnologie, Universita di Verona and INSTM, UdR Verona, Strada Le Grazie 15, I-37134 Verona (Italy)

2012-12-15

Nd{sup 3+} and Eu{sup 3+} doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3} nanostructured multiferroics (nanoparticles or nanorods) were prepared by a sol-gel route. X-Ray powder diffraction results evidence that the sodium and mixed sodium-potassium niobates show orthorhombic (Pmc2{sub 1} space group), and monoclinic structure (Pm space group), respectively, confirmed by the Raman spectra. The local structure around the trivalent lanthanides was investigated with Extended X-ray Absorption Fine Structure spectroscopy at the Ln-K edge and luminescence spectroscopy. The Ln{sup 3+} ions enter the structure by substituting the alkali metals, with a 12-fold oxygen coordination, and inducing a large amount of static disorder. The visible emission bands of the Eu{sup 3+} ions indicate that multiple sites exist for the lanthanide ions, in agreement with the EXAFS results showing the largest amount of static disorder in these samples. A possible indication of clustering of oxygen vacancies around the Ln{sub Na} Double-Prime defect is obtained by VBS calculations. - Graphical Abstract: Ln{sup 3+} doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3} nanoparticles or nanorods can be prepared by a simple sol-gel procedure. The synergy of X-ray diffraction, EXAFS and luminescence spectroscopy gives important information on the Ln{sup 3+} local environment. Highlights: Black-Right-Pointing-Pointer Nd{sup 3+} and Eu{sup 3+} doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3} nanoparticles or nanorods are prepared by sol-gel. Black-Right-Pointing-Pointer EXAFS indicates that the Ln{sup 3+} ions substitutes the Na{sup +} and K{sup +} ions, inducing a large amount of static disorder. Black-Right-Pointing-Pointer The visible emission bands of the Eu{sup 3+} ions confirm that multiple sites exist for the lanthanide ions.

Effects of Nb and Sr doping on crystal structure of epitaxial BaTiO3 thin films on MgO substrates

International Nuclear Information System (INIS)

Kim, Yongsam; Chen, Chunhua; Saiki, Atsushi; Wakiya, Naoki; Shinozaki, Kazuo; Mizutani, Nobuyasu

2002-01-01

Niobium (Nb) and strontium (Sr) doped barium titanate (BT) films were deposited by radio frequency (RF) magnetron sputtering with Nb and Sr doped BT ceramic targets, respectively. The effect of Nb and Sr doping on the crystal structure of epitaxial BaTiO 3 thin films on MgO substrates was investigated. The crystal structure of the films was examined using the reciprocal space mapping measurement. All the films exhibit a cube-on-cube relation with respect to the substrates. As the amount of doped Sr increased, both of the in-plane and out-of-plane lattice constants of Sr doped BT films slowly approached the BT bulk values. On the other hand, the lattice constants of Nb doped BT films were rapidly coming close to the bulk values. These indicated that the lattices of doped BT films were relaxed as the amount of doped elements increased. In addition, Nb doping had greater influence on the relaxation of the films than Sr doping for the same content of dopant. (author)

Evolution of the SrTiO3/MoO3 interface electronic structure: An in situ photoelectron spectroscopy study

KAUST Repository

Du, Yuanmin; Peng, Haiyang; Mao, Hongying; Jin, Kexin; Wang, Hong; Li, Feng; Gao, Xingyu; Chen, Wei; Wu, Tao

2015-01-01

Modifying the surface energetics, particularly the work function, of advanced materials is of critical importance for a wide range of surface- and interface-based devices. In this work, using in situ photoelectron spectroscopy, we investigated the evolution of electronic structure at the SrTiO3 surface during the growth of ultrathin MoO3 layers. Thanks to the large work function difference between SrTiO3 and MoO3, the energy band alignment on the SrTiO3 surface is significantly modified. The charge transfer and dipole formation at the SrTiO3/MoO3 interface leads to a large modulation of work function and an apparent doping in SrTiO3. The measured evolution of electronic structure and upward band bending suggest that the growth of ultrathin MoO3 layers is a powerful tool to modulate the surface energetics of SrTiO3, and this surface-engineering approach could be generalized to other functional oxides.

Evolution of the SrTiO3/MoO3 interface electronic structure: An in situ photoelectron spectroscopy study

KAUST Repository

Du, Yuanmin

2015-05-12

Modifying the surface energetics, particularly the work function, of advanced materials is of critical importance for a wide range of surface- and interface-based devices. In this work, using in situ photoelectron spectroscopy, we investigated the evolution of electronic structure at the SrTiO3 surface during the growth of ultrathin MoO3 layers. Thanks to the large work function difference between SrTiO3 and MoO3, the energy band alignment on the SrTiO3 surface is significantly modified. The charge transfer and dipole formation at the SrTiO3/MoO3 interface leads to a large modulation of work function and an apparent doping in SrTiO3. The measured evolution of electronic structure and upward band bending suggest that the growth of ultrathin MoO3 layers is a powerful tool to modulate the surface energetics of SrTiO3, and this surface-engineering approach could be generalized to other functional oxides.

Defect and electrical transport properties of Nb-doped SrTiO₃

DEFF Research Database (Denmark)

Blennow Tullmar, Peter; Hagen, Anke; Kammer Hansen, Kent

2008-01-01

analyzed with SEM, XRD, TGA, and XANES. The electrical conductivity of Nb-doped strontium titanate (Sr0.94Ti0.9Nb0.1O3 - sintered in 9% H-2/N-2 at 1400 degrees C for 12 h) decreased with increasing temperature and showed a phonon scattering conduction mechanism with (sigma>120 S/cm at 1000 degrees C (in 9...

The investigation of the effect of niobium artificial doping with titanium on Nb3Sn superconductors properties

International Nuclear Information System (INIS)

Nikulin, A.; Shikov, A.; Beliakov, N.; Semin, M.

1997-01-01

The effect on titanium doping of Nb filaments, and thus on the properties of bronze processed multifilamentary Nb 3 Sn wires and wires with internal tin sources with copper volume fraction up to 65 %, has been analysed. Either titanium rods or rods of the Nb-50Ti alloy, inserted in the axial area of each filament, were used as a source of titanium. The influence of doping on the quantity, composition, structure and superconducting properties of intermetallic compound Nb 3 Sn after heat treatments at 570-750 degrees C with duration up to 350 h was investigated by means of electrical measurements, optical metallography and methods of microanalysis and X-ray analysis. It was shown that the non-copper critical current density of the doped wires attained 600 and 270 A/mm 2 in 12.5 and 16 T respectively for bronze processed wires and 800 and 300 A/mm 2 for wires with internal tin source. Upper critical field calculated in accordance with Kramer's extrapolation was equal to 29-32 T

Anomalous enhancement of the thermoelectric figure of merit by V co-doping of Nb-SrTiO3

KAUST Repository

Ozdogan, K.

2012-05-10

The effect of V co-doping of Nb-SrTiO3 is studied by full-potential density functional theory. We obtain a stronger increase of the carrier density for V than for Nbdopants. While in Nb-SrTiO3 a high carrier density counteracts a high thermoelectric figure of merit, the trend is inverted by V co-doping. The mechanism leading to this behavior is explained in terms of a local spin-polarization introduced by the V ions. Our results indicate that magnetic co-doping can be a prominent tool for improving the thermoelectric figure of merit.

Anomalous enhancement of the thermoelectric figure of merit by V co-doping of Nb-SrTiO3

KAUST Repository

Ozdogan, K.; Alshareef, Husam N.; Schwingenschlö gl, Udo; Upadhyay Kahaly, M.

2012-01-01

The effect of V co-doping of Nb-SrTiO3 is studied by full-potential density functional theory. We obtain a stronger increase of the carrier density for V than for Nbdopants. While in Nb-SrTiO3 a high carrier density counteracts a high thermoelectric figure of merit, the trend is inverted by V co-doping. The mechanism leading to this behavior is explained in terms of a local spin-polarization introduced by the V ions. Our results indicate that magnetic co-doping can be a prominent tool for improving the thermoelectric figure of merit.

Dielectric, ferroelectric and piezoelectric properties of Nb{sup 5+} doped BCZT ceramics

Energy Technology Data Exchange (ETDEWEB)

Parjansri, Piewpan [Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, 50200 Chiang Mai (Thailand); Intatha, Uraiwan [School of Science, Mae Fah Luang University, 57100 Chiang Rai (Thailand); Eitssayeam, Sukum, E-mail: sukum99@yahoo.com [Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, 50200 Chiang Mai (Thailand); Materials Science Research Center, Faculty of Science, Chiang Mai University, 50200 Chiang Mai (Thailand)

2015-05-15

Highlights: • Average grain size of BCZT ceramic decreased with the increasing Nb{sup 5+} doping. • Dielectric constant value is enhanced with Nb{sup 5+} doping. • Dielectric loss of BCZT − x Nb{sup 5+} ceramics was less than 0.03 at room temperature (1 kHz). • Piezoelectric coefficient decreased with the increasing Nb{sup 5+} doping. • The relaxation behavior is enhanced with the doping of Nb{sup 5+}. - Abstract: This work investigated the electrical properties of Nb{sup 5+} (0.0–1.0 mol%) doped with Ba{sub 0.90}Ca{sub 0.10}Zr{sub 0.10}Ti{sub 0.90}O{sub 3} while adding 1 mol% of Ba{sub 0.90}Ca{sub 0.10}Zr{sub 0.10}Ti{sub 0.90}O{sub 3} seeds. The mixed powder was ball milled for 24 h, calcined and sintered at 1200 °C for 2 h and 1450 °C for 4 h, respectively. The XRD patterns of the ceramic samples were investigated by X-ray diffraction. The electrical properties of ceramics were measured and the results indicated that all samples show a pure perovskite phase with no secondary phase. Density and average grain size values were in the range of 5.60–5.71 g/cm{sup 3} and 12.62–1.86 μm, respectively. The highest dielectric constant, ϵ{sub r} at room temperature (1 kHz) was 4636 found at 1.0 mol% Nb. The dielectric loss, tan δ was less than 0.03 for all samples at room temperature (1 kHz). Other electrical properties, P{sub r}, d{sub 33} and k{sub p} values were decreased with Nb doped relates to the decreasing grain size in BCZT ceramics. Moreover, the degrees of phase transition diffuseness and relaxation behavior were observed in the higher Nb doping.

Thickness-dependent resistance switching in Cr-doped SrTiO3

Science.gov (United States)

Kim, TaeKwang; Du, Hyewon; Kim, Minchang; Seo, Sunae; Hwang, Inrok; Kim, Yeonsoo; Jeon, Jihoon; Lee, Sangik; Park, Baeho

2012-09-01

The thickness-dependent bipolar resistance-switching behavior was investigated for epitaxiallygrown Cr-doped SrTiO3 (Cr-STO). All the pristine devices of different thickness showed polarity-independent symmetric current-voltage characteristic and the same space-charge-limited conduction mechanism. However, after a forming process, the resultant conduction and switching phenomena were significantly different depending on the thickness of Cr-STO. The forming process itself was highly influenced by resistance value of each pristine device. Based on our results, we suggest that the resistance-switching mechanism in Cr-STO depends not only on the insulating material's composition or the contact metal as previously reported but also on the initial resistance level determined by the geometry and the quality of the insulating material. The bipolar resistance-switching behaviors in oxide materials of different thicknesses exhibit mixed bulk and interface switching. This indicates that efforts in resistance-based memory research should be focused on scalability or process method to control a given oxide material in addition to material type and device structure.

Nanostructured rare earth doped Nb2O5: Structural, optical properties and their correlation with photonic applications

International Nuclear Information System (INIS)

Pereira, Rafael Ramiro; Aquino, Felipe Thomaz; Ferrier, Alban; Goldner, Philippe; Gonçalves, Rogéria R.

2016-01-01

In the present work, we report on a systematic study on structural and spectroscopic properties Eu 3+ and Er 3+ -doped Nb 2 O 5 prepared by sol–gel method. The Eu 3+ ions were used as structural probe to determine the symmetry sites occupied by lanthanide ions. The Eu 3+ -doped Nb 2 O 5 nanocrystalline powders were annealed at different temperatures to verify how the different Nb 2 O 5 crystalline phases affect the structure and the luminescence properties. Er 3+ -doped Nb 2 O 5 was prepared showing an intense NIR luminescence, and, visible luminescence on the green and red, deriving from upconversion process. The synthetized materials can find widespread applicability in photonics as red luminophor for white LED (with tricolor), optical amplifiers and upconverter materials. - Highlights: • Vis and NIR emission from nanostructured lanthanide doped Nb 2 O 5 . • Eu 3+ -doped Nb 2 O 5 as Red luminophor. • Multicolor tunability of intense upconversion emission from lanthanide doped Nb 2 O 5 . • Potential application as biological markers. • Broad band NIR emission.

Effective improvement of interface modified strontium titanate based solid oxide fuel cell anodes by infiltration with nano-sized palladium and gadolinium-doped cerium oxide

DEFF Research Database (Denmark)

Abdul Jabbar, Mohammed Hussain; Høgh, Jens Valdemar Thorvald; Zhang, Wei

2013-01-01

The development of low temperature solid oxide fuel cell (SOFC) anodes by infiltration of Pd/Gd-doped cerium oxide (CGO) electrocatalysts in Nb-doped SrTiO3 (STN) backbones has been investigated. Modification of the electrode/electrolyte interface by thin layer of spin-coated CGO (400-500 nm) con...

Carrier compensation mechanism in heavily Nb-doped anatase Ti{sub 1-x}Nb{sub x}O{sub 2+{delta}} epitaxial thin films

Energy Technology Data Exchange (ETDEWEB)

Nogawa, H; Chikamatsu, A; Hirose, Y; Hasegawa, T [Department of Chemistry, University of Tokyo, Tokyo 113-0033 (Japan); Nakao, S [Kanagawa Academy of Science and Technology (KAST), Kawasaki 213-0012 (Japan); Kumigashira, H; Oshima, M, E-mail: chikamatsu@chem.s.u-tokyo.ac.jp [Department of Applied Chemistry, University of Tokyo, Tokyo 113-8656 (Japan)

2011-09-14

We investigated the electronic structures of anatase Ti{sub 1-x}Nb{sub x}O{sub 2+{delta}} (TNO) thin films as a function of Nb concentration x using photoemission spectroscopy (PES) measurements to elucidate the origin of the abrupt decrease in carrier activation in heavily Nb-doped regime. The existing intensity ratio of Nb{sup 5+} evaluated from Nb 3d core-level PES spectra maintained a constant value of {approx}0.8 at x = 0.06-0.3, implying that electron carriers generated by Nb doping are compensated by p-type defects. Ti 2p-3d and O1s-2p resonant PES measurements of x = 0.06-0.3 films revealed that the in-gap states positioned {approx}1 eV below the Fermi level (E{sub F}) have a mixed character of Ti 3d and O 2p orbitals, whereas the states at E{sub F} mainly have a Ti 3d nature. We proposed a carrier compensation mechanism that interstitial oxygen atoms strongly combined with surrounding Nb atoms kill conduction electrons in heavily Nb-doped anatase TiO{sub 2}.

Efficient degradation of Methylene Blue dye over highly reactive Cu doped strontium titanate (SrTiO3) nanoparticles photocatalyst under visible light.

Science.gov (United States)

Rahman, Qazi Inamur; Ahmad, Musheer; Misra, Sunil Kumar; Lohani, Minaxi

2012-09-01

Visible light induced photocatalysts of Cu doped SrTiO3 (Cu/SrTiO3) nanoparticles with the size -60-75 nm were prepared via facile sol-gel method. The morphological, optical, crystalline properties and compositions of synthesized Cu/SrTiO3 nanoparticles were thoroughly characterized by field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD), ultra violet-visible spectroscopy (UV-Vis) and energy dispersive X-ray (EDX). A significant red shift in the UV-diffused reflectance spectrum was observed and the absorption edge shifted to visible region by the Cu doping. Surprisingly, the band gap of SrTiO3 was changed from 3.2 eV drop to 2.96 eV. The photocatalytic activity of the synthesized Cu/SrTiO3 nanoparticles was demonstrated for the degradation of Methylene Blue dye under visible light irradiation. The formation of new acceptor region in Cu/SrTiO3 was responsible for high photocatalytic activity of Cu/SrTiO3 nanoparticles. The results showed that the Methylene Blue dye was degraded by -66% within time span of 2 h over the Cu/SrTiO3 nanoparticles. This dye degradation reaction followed the Langmuir-Hinshelwood kinetics and also exhibited first order reaction rate. The calculated rate constant for the degradation reaction following first order kinetics was k = 0.0016 min(-1).

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

Directory of Open Access Journals (Sweden)

S. Gariglio

2016-06-01

Full Text Available In this review, we focus on the celebrated interface between two band insulators, LaAlO3 and SrTiO3, that was found to be conducting, superconducting, and to display a strong spin-orbit coupling. We discuss the formation of the 2-dimensional electron liquid at this interface, the particular electronic structure linked to the carrier confinement, the transport properties, and the signatures of magnetism. We then highlight distinctive characteristics of the superconducting regime, such as the electric field effect control of the carrier density, the unique tunability observed in this system, and the role of the electronic subband structure. Finally we compare the behavior of Tc versus 2D doping with the dome-like behavior of the 3D bulk superconductivity observed in doped SrTiO3. This comparison reveals surprising differences when the Tc behavior is analyzed in terms of the 3D carrier density for the interface and the bulk.

Optical properties of Mg2+, Yb3+, and Ho3+ tri-doped LiNbO3 crystals

Science.gov (United States)

Dai, Li; Liu, Chun-Rui; Tan, Chao; Yan, Zhe-Hua; Xu, Yu-Heng

2017-04-01

A series of LiNbO3 crystals tri-doped with Mg{}2+, Yb{}3+, and Ho{}3+ are grown by the conventional Czochraski technique. The concentrations of Mg{}2+, Yb{}3+, and Ho{}3+ ions in Mg:Yb:Ho:LiNbO3 crystals are measured by using an inductively coupled plasma atomic emission spectrometry. The x-ray diffraction is proposed to determine the lattice constant and analyze the internal structure of the crystal. The light-induced scattering of Mg:Yb:Ho:LiNbO3 crystal is quantitatively described via the threshold effect of incident exposure energy flux. The exposure energy ({E}{{r}}) is calculated to discuss the optical damage resistance ability. The exposure energy of Mg(7 mol):Yb:Ho:LiNbO3 crystal is 709.17 J/cm2, approximately 425 times higher than that of the Mg(1 mol):Yb:Ho:LiNbO3 crystal in magnitude. The blue, red, and very intense green bands of Mg:Yb:Ho:LiNbO3 crystal are observed under the 980-nm laser excitation to evaluate the up-conversion emission properties. The dependence of the emission intensity on pumping power indicates that the up-conversion emission is a two-photon process. The up-conversion emission mechanism is discussed in detail. This study indicates that Mg:Yb:Ho:LiNbO3 crystal can be applied to the fabrication of new multifunctional photoluminescence devices. Project supported by the National Natural Science Foundation of China (Grant No. 51301055), the Youth Science Fund of Heilongjiang Province, China (Grant No. QC2015061), the Special Funds of Harbin Innovation Talents in Science and Technology Research, China (Grant No. 2015RQQXJ045 ), and the Science Funds for the Young Innovative Talents of Harbin University of Science and Technology, China (Grant No. 201501).

Structural and vibrational investigations of Nb-doped TiO2 thin films

International Nuclear Information System (INIS)

Uyanga, E.; Gibaud, A.; Daniel, P.; Sangaa, D.; Sevjidsuren, G.; Altantsog, P.; Beuvier, T.; Lee, Chih Hao; Balagurov, A.M.

2014-01-01

Highlights: • We studied the evolutions of structure for TiO 2 thin film as changes with Nb doping and temperatures. • Up to 800 °C, the grain size of Nb 0.1 Ti 0.9 O 2 is smaller than for pure TiO 2 because doped Nb hinders the growth of the TiO 2 grains. • There was no formation of the rutile phase at high temperature. • Nb doped TiO 2 films have high electron densities at 400–700 °C. • Nb dope extends the absorbance spectra of TiO 2 which leads to the band gap reduce. - Abstract: Acid-catalyzed sol–gel and spin-coating methods were used to prepare Nb-doped TiO 2 thin film. In this work, we studied the effect of niobium doping on the structure, surface, and absorption properties of TiO 2 by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectometry (XRR), X-ray photoelectron spectroscopy (XPS), Raman, and UV–vis absorption spectroscopy at various annealing temperatures. EDX spectra show that the Nb:Ti atomic ratios of the niobium-doped titania films are in good agreement with the nominal values (5 and 10%). XPS results suggest that charge compensation is achieved by the formation of Ti vacancies. Specific niobium phases are not observed, thus confirming that niobium is well incorporated into the titania crystal lattice. Thin films are amorphous at room temperature and the formation of anatase phase appeared at an annealing temperature close to 400 °C. The rutile phase was not observed even at 900 °C (XRD and Raman spectroscopy). Grain sizes and electron densities increased when the temperature was raised. Nb-doped films have higher electron densities and lower grain sizes due to niobium doping. Grain size inhibition can be explained by lattice stress induced by the incorporation of larger Nb 5+ ions into the lattice. The band gap energy of indirect transition of the TiO 2 thin films was calculated to be about 3.03 eV. After niobium doping, it decreased to 2.40 eV

Universality of electron mobility in LaAlO3/SrTiO3 and bulk SrTiO3

Science.gov (United States)

Trier, Felix; Reich, K. V.; Christensen, Dennis Valbjørn; Zhang, Yu; Tuller, Harry L.; Chen, Yunzhong; Shklovskii, B. I.; Pryds, Nini

2017-08-01

Metallic LaAlO3/SrTiO3 (LAO/STO) interfaces attract enormous attention, but the relationship between the electron mobility and the sheet electron density, ns, is poorly understood. Here, we derive a simple expression for the three-dimensional electron density near the interface, n3 D , as a function of ns and find that the mobility for LAO/STO-based interfaces depends on n3 D in the same way as it does for bulk doped STO. It is known that undoped bulk STO is strongly compensated with N ≃5 ×1018 cm-3 background donors and acceptors. In intentionally doped bulk STO with a concentration of electrons n3 DN , the mobility collapses because scattering happens on n3 D intentionally introduced donors. For LAO/STO, the polar catastrophe which provides electrons is not supposed to provide an equal number of random donors and thus the mobility should be larger. The fact that the mobility is still the same implies that for the LAO/STO, the polar catastrophe model should be revisited.

Large thermoelectric power factor in Pr-doped SrTiO3-δ ceramics via grain-boundary-induced mobility enhancement

KAUST Repository

Mehdizadeh Dehkordi, Arash

2014-04-08

We report a novel synthesis strategy to prepare high-performance bulk polycrystalline Pr-doped SrTiO3 ceramics. A large thermoelectric power factor of 1.3 W m-1 K-1 at 500 °C is achieved in these samples. In-depth investigations of the electronic transport and microstructure suggest that this significant improvement results from a substantial enhancement in carrier mobility originating from the formation of Pr-rich grain boundaries. This work provides new directions to higher performance oxide thermoelectrics as well as possibly other properties and applications of this broadly functional perovskite material. © 2014 American Chemical Society.

Large thermoelectric power factor in Pr-doped SrTiO3-δ ceramics via grain-boundary-induced mobility enhancement

KAUST Repository

Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna K.; Darroudi, Taghi; Graff, Jennifer W.; Schwingenschlö gl, Udo; Alshareef, Husam N.; Tritt, Terry M.

2014-01-01

We report a novel synthesis strategy to prepare high-performance bulk polycrystalline Pr-doped SrTiO3 ceramics. A large thermoelectric power factor of 1.3 W m-1 K-1 at 500 °C is achieved in these samples. In-depth investigations of the electronic transport and microstructure suggest that this significant improvement results from a substantial enhancement in carrier mobility originating from the formation of Pr-rich grain boundaries. This work provides new directions to higher performance oxide thermoelectrics as well as possibly other properties and applications of this broadly functional perovskite material. © 2014 American Chemical Society.

The effect of Nd and Mg doping on the micro-Raman spectra of LiNbO3 single-crystals

International Nuclear Information System (INIS)

Quispe-Siccha, R; Villagran-Muniz, M; MejIa-Uriarte, E V; Jaque, D; GarcIa Sole, J; Jaque, F; Sato-Berru, R Y; Camarillo, E; Hernandez A, J; Murrieta S, H

2009-01-01

The LiNbO 3 congruent crystals doped with small Nd concentrations, 1 (TO 1 ) and A 1 (TO 2 ) modes, the half-width composition and the area ratio of the A 1 (TO 4 ) and E(TO 8 ) bands, we reached several conclusions about the incorporation mechanism of the Nd and Mg ions into the LiNbO 3 lattice. Likewise the Raman shift and half-width of the E(TO 1 ) and E(TO 7 ) modes were investigated in the Z direction. Results indicate that Mg and Nd ions are located in the Li site for low doping concentrations and for larger concentrations there is a replacement in both Li and Nb ion sites.

Effect of Nb-doped TiO{sub 2} on nanocomposited aligned ZnO nanorod/TiO{sub 2}:Nb for dye-sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Saurdi, I., E-mail: saurdy788@gmail.com; Ishak, A. [NANO-ElecTronic Centre (NET), Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM),40450 Shah Alam, Selangor (Malaysia); UiTM Sarawak Kampus Kota Samarahan Jalan Meranek, Sarawak (Malaysia); Shafura, A. K.; Azhar, N. E. A.; Mamat, M. H. [NANO-ElecTronic Centre (NET), Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM),40450 Shah Alam, Selangor (Malaysia); Malek, M. F.; Rusop, M. [NANO-ElecTronic Centre (NET), Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM),40450 Shah Alam, Selangor (Malaysia); NANO-SciTech Centre (NST), (Centre for Nano-Science and Nano-Technology), Institute of Science, Universiti Teknologi MARA - UiTM, 40450 Shah Alam, Selangor (Malaysia); Alrokayan, A. H. Salman; Khan, Haseeb A. [Department of Biochemistry, College of Science, Bldg. 5, King Saud University (KSU) P.O: 2455 Riyadh 1145 (Saudi Arabia)

2016-07-06

The Nb-doped TiO{sub 2} films were deposited on glass substrate at different Nb concentrations of 0 at.%, 1 at.%, 3 at.%, 5 at.% and 7 at.%, respectively and their electrical and structural properties were investigated. Subsequently, the Nb-doped TiO{sub 2} films were deposited on top of aligned ZnO Nanorod on ITO glass substrates using spin coating technique. The nanocomposited aligned ZnO nanorod/Nb-doped TiO{sub 2} (TiO{sub 2}:Nb) were coated with different Nb concentrations of 0 at.%, 1 at.%, 3 at.%, 5 at.% and 7 at.%, respectively. The Dye-sensitized solar cells were fabricated from the nanocomposited aligned ZnO nanorod/TiO{sub 2}:Nb photoanodes and their effects on the performance of the DSSCs were investigated. From the solar simulator measurement of DSSC the solar energy conversion efficiency (η) of 5.376% under AM 1.5 was obtained for the ZnO nanorod/TiO{sub 2}:Nb-5at.%.

Epitaxial growth of Er, Ti doped LiNbO3 films prepared by sol-gel method

International Nuclear Information System (INIS)

Takahashi, Makoto; Yoshiga, Tsuyoshi; Kajitani, Naofumi; Takeda, Yuki; Sato, Shoji; Wakita, Koichi; Ohnishi, Naoyuki; Hotta, Kazutoshi; Kurachi, Masato

2006-01-01

Erbium (Er 3+ ) doped lithium niobate (LiNbO 3 ) thick films were deposited on z-cut congruent LiNbO 3 (LN) substrate by the sol-gel method from the 0.20 mol/dm 3 precursor solution containing various Er 3+ concentration and 0.10 mol/dm 3 poly(vinyl alcohol) (PVA), and their crystal characteristics were evaluated. The Er 3+ concentration in the LN film was controlled by the Er 3+ concentration in the starting solution. The orientation relationships between Er doped LN films and substrates were determined by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and (006) oriented Er doped LN epitaxial layers with parallel epitaxial relationships could be grown on the z-cut LN wafer. Moreover, it was made clear from the electron beam diffraction measurements that the film came to be polycrystalline, when the Er concentration was over 3 mol%. The refractive index of Er-doped LN films decreased with increasing Er concentration. 1.5 mol% Ti: 1.0 mol% Er LN films, which acted as a waveguide, were prepared by our so-gel method. It showed the 1530 nm emission by 980 nm excitation, which was considered to be due to the Er 3+ corresponding to the 4 I 13/2 → 4 I 15/2 transition. (author)

Thermoelectric properties of strontium titanate superlattices incorporating niobium oxide nanolayers

KAUST Repository

Sarath Kumar, S. R.; Hedhili, Mohamed N.; Cha, Dong Kyu; Tritt, Terry M.; Alshareef, Husam N.

2014-01-01

A novel superlattice structure based on epitaxial nanoscale layers of NbOx and Nb-doped SrTiO3 is fabricated using a layer-by-layer approach on lattice matched LAO substrates. The absolute Seebeck coefficient and electrical conductivity of the [(NbOx) a/(Nb-doped SrTiO3)b]20 superlattices (SLs) were found to increase with decreasing layer thickness ratio (a/b ratio), reaching, at high temperatures, a power factor that is comparable to epitaxial Nb-doped SrTiO3 (STNO) films (∼0.7 W m-1 K-1). High temperature studies reveal that the SLs behave as n-type semiconductors and undergo an irreversible change at a varying crossover temperature that depends on the a/b ratio. By use of high resolution X-ray photoelectron spectroscopy and X-ray diffraction, the irreversible changes are identified to be due to a phase transformation from cubic NbO to orthorhombic Nb2O5, which limits the highest temperature of stable operation of the superlattice to 950 K. © 2014 American Chemical Society.

Thermoelectric properties of strontium titanate superlattices incorporating niobium oxide nanolayers

KAUST Repository

Sarath Kumar, S. R.

2014-04-22

A novel superlattice structure based on epitaxial nanoscale layers of NbOx and Nb-doped SrTiO3 is fabricated using a layer-by-layer approach on lattice matched LAO substrates. The absolute Seebeck coefficient and electrical conductivity of the [(NbOx) a/(Nb-doped SrTiO3)b]20 superlattices (SLs) were found to increase with decreasing layer thickness ratio (a/b ratio), reaching, at high temperatures, a power factor that is comparable to epitaxial Nb-doped SrTiO3 (STNO) films (∼0.7 W m-1 K-1). High temperature studies reveal that the SLs behave as n-type semiconductors and undergo an irreversible change at a varying crossover temperature that depends on the a/b ratio. By use of high resolution X-ray photoelectron spectroscopy and X-ray diffraction, the irreversible changes are identified to be due to a phase transformation from cubic NbO to orthorhombic Nb2O5, which limits the highest temperature of stable operation of the superlattice to 950 K. © 2014 American Chemical Society.

Effect of concurrent Mg/Nb-doping on dielectric properties of Ba0.45Sr0.55TiO3 thin films

Science.gov (United States)

Alema, Fikadu; Reich, Michael; Reinholz, Aaron; Pokhodnya, Konstantin

2013-08-01

Composition, microstructure, and dielectric properties of undoped and Ba(Mg1/3Nb2/3)O3 (BMN) doped Ba0.45Sr0.55TiO3 (BST) thin films deposited via rf. magnetron sputtering on platinized alumina substrates have been investigated. The analysis of microstructure has shown that despite the sizable effect of doping on the residual stress, the latter is partially compensated by the thermal expansion coefficient mismatch, and its influence on the BST film crystal structure is insignificant. It was revealed that BMN doped film demonstrated an average (over 2000 devices) of 52.5% tunability at 640 kV/cm, which is ˜8% lower than the value for the undoped film. This drop is associated with the presence of Mg ions in BMN; however, the effect of Mg doping is partially compensated by that of Nb ions. The decrease in grain size upon doping may also contribute to the tunability drop. Doping with BMN allows achievement of a compensation concentration yielding no free carriers and resulting in significant leakage current reduction when compared with the undoped film. In addition, the presence of large amounts of empty shallow traps related to NbTi• allows localizing free carriers injected from the contacts thus extending the device control voltage substantially above 10 V.

Dielectric properties of BaMg1/3Nb2/3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

Science.gov (United States)

Alema, Fikadu; Pokhodnya, Konstantin

2015-11-01

Ba(Mg1/3Nb2/3)O3 (BMN) doped and undoped Ba0.45Sr0.55TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss (˜38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg2+ whose detrimental effect on tunability is partially compensated by small Nb5+ as the two substitute Ti4+ in the BST. The coupling between MgTi″ and VO•• charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300-450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from MgTi″, VO•• and NbTi• charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole-Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled NbTi• sitting as a positive trap center at the shallow donor level of the BST.

Adsorptive and photocatalytic properties of S-doped SrTiO3 under simulated solar irradiation

Science.gov (United States)

Huynh, Phu Chi; Le, Vien Minh

2017-09-01

S-doped SrTiO3 (SSTO) nanoparticles were synthesized using the sol-gel method with Sr(NO3)2, n- Ti(OC4H9)4, and Thiourea as precursors. Several analytical techniques including XRD, SEM, BET were employed to characterize the physical properties of the product. High crystalline perovskite of SSTO powder was synthesized at 700 °C calcined temperature with the specific surface area of 20.71 m2/g. UV-Vis diffuse reflectance spectra results of STO and 5SSTO present band gap energy of 3.2 and 2.95 eV respectively. Photocatalytic activity was determined through the photodegradation of Congo Red at the initial concentrations of 70 ppm under simulated solar irradiation using 26W mercury lamp (120V - 60Hz). The decompositions of approximately 90.4% was obtained after 210 minutes of illumination. The photocatalyst was stable in aqueous solution that its photocatalytic activity was merely reduced by 9% even after 4 reusing iterations.

Nanostructured rare earth doped Nb{sub 2}O{sub 5}: Structural, optical properties and their correlation with photonic applications

Energy Technology Data Exchange (ETDEWEB)

Pereira, Rafael Ramiro; Aquino, Felipe Thomaz [Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Ribeirão Preto, SP CEP 14040-901 (Brazil); Ferrier, Alban [PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 75005 Paris (France); Sorbonne Universités, UPMC Univ Paris 06, 75005 Paris (France); Goldner, Philippe [PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 75005 Paris (France); Gonçalves, Rogéria R., E-mail: rrgoncalves@ffclrp.usp.br [Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Ribeirão Preto, SP CEP 14040-901 (Brazil)

2016-02-15

In the present work, we report on a systematic study on structural and spectroscopic properties Eu{sup 3+} and Er{sup 3+}-doped Nb{sub 2}O{sub 5} prepared by sol–gel method. The Eu{sup 3+} ions were used as structural probe to determine the symmetry sites occupied by lanthanide ions. The Eu{sup 3+}-doped Nb{sub 2}O{sub 5} nanocrystalline powders were annealed at different temperatures to verify how the different Nb{sub 2}O{sub 5} crystalline phases affect the structure and the luminescence properties. Er{sup 3+}-doped Nb{sub 2}O{sub 5} was prepared showing an intense NIR luminescence, and, visible luminescence on the green and red, deriving from upconversion process. The synthetized materials can find widespread applicability in photonics as red luminophor for white LED (with tricolor), optical amplifiers and upconverter materials. - Highlights: • Vis and NIR emission from nanostructured lanthanide doped Nb{sub 2}O{sub 5}. • Eu{sup 3+}-doped Nb{sub 2}O{sub 5} as Red luminophor. • Multicolor tunability of intense upconversion emission from lanthanide doped Nb{sub 2}O{sub 5}. • Potential application as biological markers. • Broad band NIR emission.

Reflectance of Co- and Nb-doped BaTiO3 for photon energies from 1.8 to 70 eV

International Nuclear Information System (INIS)

Goudonnet, J.P.; Godefroy, G.; Inagaki, T.; Moretti, P.; Williams, M.W.; Arakawa, E.T.

1985-01-01

The reflectance spectra of Co- and Nb-doped BaTiO 3 crystals have been measured for photon energies from 1.8 to 70 eV. For both types of crystal, structures observed in the 1.8 to 2.3 eV range can be attributed to the presence of residual impurities. Between 2.3 and 3.2 eV the peaks in the reflectance of the Co-doped crystal are found to be of an acceptor charge transfer type. For Nb-doped crystals structures appear at the bottom of the conduction band. For energies larger than 3.2 eV the spectra are characteristic of pure BaTiO 3 crystals, in reasonable agreement with those determined by Baeuerle et al. and calculated by Michel-Calendini and Moretti. 15 refs., 4 figs., 1 tab

Impact of Nb vacancies and p-type doping of the NbCoSn-NbCoSb half-Heusler thermoelectrics.

Science.gov (United States)

Ferluccio, Daniella A; Smith, Ronald I; Buckman, Jim; Bos, Jan-Willem G

2018-02-07

The half-Heuslers NbCoSn and NbCoSb have promising thermoelectric properties. Here, an investigation of the NbCo 1+y Sn 1-z Sb z (y = 0, 0.05; 0 ≤ z ≤ 1) solid-solution is presented. In addition, the p-type doping of NbCoSn using Ti and Zr substitution is investigated. Rietveld analysis reveals the gradual creation of Nb vacancies to compensate for the n-type doping caused by the substitution of Sb in NbCoSn. This leads to a similar valence electron count (∼18.25) for the NbCo 1+y Sn 1-z Sb z samples (z > 0). Mass fluctuation disorder due to the Nb vacancies strongly decreases the lattice thermal conductivity from 10 W m -1 K -1 (z = 0) to 4.5 W m -1 K -1 (z = 0.5, 1). This is accompanied by a transition to degenerate semiconducting behaviour leading to large power factors, S 2 /ρ = 2.5-3 mW m -1 K -2 and figures of merit, ZT = 0.25-0.33 at 773 K. Ti and Zr can be used to achieve positive Seebeck values, e.g. S = +150 μV K -1 for 20% Zr at 773 K. However, the electrical resistivity, ρ 323K = 27-35 mΩ cm, remains too large for these materials to be considered useful p-type materials.

Substitution of Nb doping on the structural, microstructural and electrical properties in PZT films

International Nuclear Information System (INIS)

Haccart, T.; Remiens, D.; Cattan, E.

2003-01-01

Undoped and niobium (Nb) doped Pb 1-y (Zr 0.54 Ti 0.46 ) 1-y Nb y O 3 have been deposited by sputtering on Pt metallized silicon substrates. The niobium concentration, y, was varied from 1 to 7 at.% by 1 at.%. The Zr/Ti ratio was fixed to 54/46 corresponding to the Morphotropic Phase Boundary. Structural, microstructural, and electrical properties were evaluated depending on Nb content. The films (doped and undoped) present a (1 1 1)-preferred orientation. The Nb doping induces an increase of the grain size and as it was observed in bulk materials the dielectric constant (ε r ) and the piezoelectric coefficients (e 31 and d 33 ) reach their maximum for low Nb concentration (2 at.%). The remnant and the maximum polarizations increase as the coercive field decreased slightly with the Nb concentration. The internal electric field increases with Nb content; as a result, the 'self-polarization' of the films (polarization measured without poling treatment) is enhanced with niobium substitution. In term of fatigue behavior, it was found that switching endurance characteristics are maximum for low Nb doping level

Substitution of Nb doping on the structural, microstructural and electrical properties in PZT films

Energy Technology Data Exchange (ETDEWEB)

Haccart, T.; Remiens, D.; Cattan, E

2003-01-15

Undoped and niobium (Nb) doped Pb{sub 1-y}(Zr{sub 0.54}Ti{sub 0.46}){sub 1-y}Nb{sub y}O{sub 3} have been deposited by sputtering on Pt metallized silicon substrates. The niobium concentration, y, was varied from 1 to 7 at.% by 1 at.%. The Zr/Ti ratio was fixed to 54/46 corresponding to the Morphotropic Phase Boundary. Structural, microstructural, and electrical properties were evaluated depending on Nb content. The films (doped and undoped) present a (1 1 1)-preferred orientation. The Nb doping induces an increase of the grain size and as it was observed in bulk materials the dielectric constant ({epsilon}{sub r}) and the piezoelectric coefficients (e{sub 31} and d{sub 33}) reach their maximum for low Nb concentration (2 at.%). The remnant and the maximum polarizations increase as the coercive field decreased slightly with the Nb concentration. The internal electric field increases with Nb content; as a result, the 'self-polarization' of the films (polarization measured without poling treatment) is enhanced with niobium substitution. In term of fatigue behavior, it was found that switching endurance characteristics are maximum for low Nb doping level.

Fabrication and characterization of perovskite-type solar cells with Nb-doped TiO{sub 2} layers

Energy Technology Data Exchange (ETDEWEB)

Saito, Jo; Oku, Takeo, E-mail: oku@mat.usp.ac.jp; Suzuki, Atsushi; Akiyama, Tsuyoshi [The University of Shiga Prefecture, Hikone, Shiga 522-8533 (Japan)

2016-02-01

Organic-inorganic hybrid heterojunction solar cells containing perovskite CH{sub 3}NH{sub 3}PbI{sub 3} using Nb-doped TiO{sub 2} as an electron-transporting layer were fabricated and characterized. Nb-doped TiO{sub 2} layer showed an improvement of the short-circuit current density and power conversion efficiency using Ti{sub 0.95}Nb{sub 0.05}O{sub 2}.

Epitaxial Pb(Mg1/3Nb2/3)O3 thin films synthesized by metal-organic chemical vapor deposition

International Nuclear Information System (INIS)

Bai, G. R.; Streiffer, S. K.; Baumann, P. K.; Auciello, O.; Ghosh, K.; Stemmer, S.; Munkholm, A.; Thompson, Carol; Rao, R. A.; Eom, C. B.

2000-01-01

Metal-organic chemical vapor deposition was used to prepare Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) thin films on (001) SrTiO 3 and SrRuO 3 /SrTiO 3 substrates, using solid Mg β-diketonate as the Mg precursor. Parameters including the precursor ratio in the vapor phase, growth temperature, growth rate, and reaction pressure in the reactor chamber were varied in order to determine suitable growth conditions for producing phase-pure, epitaxial PMN films. A cube-on-cube orientation relationship between the thin film and the SrTiO 3 substrate was found, with a (001) rocking curve width of 0.1 degree sign , and in-plane rocking-curve width of 0.8 degree sign . The root-mean-square surface roughness of a 200-nm-thick film on SrTiO 3 was 2 to 3 nm as measured by scanning probe microscopy. The zero-bias dielectric constant and loss measured at room temperature and 10 kHz for a 200-nm-thick film on SrRuO 3 /SrTiO 3 were approximately 1100 and 2%, respectively. The remnant polarization for this film was 16 μC/cm 2 . (c) 2000 American Institute of Physics

Efficient conversion from UV light to near-IR emission in Yb{sup 3+}-doped triple-layered perovskite CaLaNb{sub 3}O{sub 10}

Energy Technology Data Exchange (ETDEWEB)

Lu, Yuting; Li, Yuze; Qin, Lin; Huang, Yanlin [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); Qin, Chuanxiang, E-mail: qinchuanxiang@suda.edu.cn [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 (China); Tsuboi, Taiju [Jiangsu-Singapore Joint Research Center for Organic/Bio-Electronics & Information Displays and Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 (China); Huang, Wei, E-mail: wei-huang@njtech.edu.cn [Jiangsu-Singapore Joint Research Center for Organic/Bio-Electronics & Information Displays and Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816 (China)

2015-04-15

Graphical abstract: CaRNb{sub 3}O{sub 10} is a self-activated oxide due to charge transfer transition in octahedral NbO{sub 6} groups. CaLaNb{sub 3}O{sub 10}:Yb{sup 3+} presents intense IR emission due to the cooperative energy transfer from host (NbO{sub 6}) to Yb{sup 3+} is responsible. It could be expected to be potentially applicable for enhancing photovoltaic conversion efficiency of Si-based solar cells. - Abstract: Yb{sup 3+}-doped triple-layered perovskite CaLaNb{sub 3}O{sub 10} micro-particles were synthesized via the solid-state reaction method. The crystal structure and morphology of the polycrystalline samples were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. The reflectance spectra, photoluminescence (PL) excitation and emission spectra, the decay curves, and the absolute quantum efficiency (QE) of the near-infrared (NIR) emission (910–1100 nm) were measured. Under excitation of UV light, Yb{sup 3+}-doped perovskite shows an intense NIR emission attributed to the {sup 2}F{sub 5/2} → {sup 2}F{sub 7/2} transitions of Yb{sup 3+} ions, which could match maximum spectral response of a Si-based solar cell. This is beneficial for its possible application in an enhancement of the photovoltaic conversion efficiency of solar energy utilization. The efficient energy transfer in Yb{sup 3+}-doped CaLaNb{sub 3}O{sub 10} from NbO{sub 6} groups into Yb{sup 3+} ions was confirmed by the spectra and fluorescent decay measurements. Cooperative energy transfer (CET) was supposed to be the NIR emission mechanism.

Visible-light-driven photoelectrochemical and photocatalytic performances of Cr-doped SrTiO3/TiO2 heterostructured nanotube arrays.

Science.gov (United States)

Jiao, Zhengbo; Chen, Tao; Xiong, Jinyan; Wang, Teng; Lu, Gongxuan; Ye, Jinhua; Bi, Yingpu

2013-01-01

Well-aligned TiO2 nanotube arrays have become of increasing significance because of their unique highly ordered array structure, high specific surface area, unidirectional charge transfer and transportation features. However, their poor visible light utilization as well as the high recombination rate of photoexcited electron-hole pairs greatly limited their practical applications. Herein, we demonstrate the fabrication of visible-light-responsive heterostructured Cr-doped SrTiO3/TiO2 nanotube arrays by a simple hydrothermal method, which facilitate efficient charge separation and thus improve the photoelectrochemical as well as photocatalytic performances.

Effect of Nb doping on electrochemical properties of LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} at high cutoff voltage for lithium-ion battery

Energy Technology Data Exchange (ETDEWEB)

Wu, Jiefan [School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130 (China); Liu, Hongguang, E-mail: hongguangliu_01@163.com [School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130 (China); CNOOC Tianjin Chemical Research & Design Institute, Tianjin 300131 (China); Ye, Xuehai; Xia, Jiping; Lu, Yang; Lin, Chaowang; Yu, Xiaowei [CNOOC Tianjin Chemical Research & Design Institute, Tianjin 300131 (China)

2015-09-25

Highlights: • Nb substituted LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3−x}Nb{sub x}O{sub 2} (x = 0–0.03) was prepared by sol–gel method. • 2% Nb-substituted sample showed better cycle performance at high cutoff voltage. • Ex situ analysis was used to show the structure changes of Nb-doped samples. - Abstract: Nb doped cathode materials with the formula LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3−x}Nb{sub x}O{sub 2} (x = 0, 0.01, 0.02, 0.03) have been prepared successfully by sol–gel method. The effect of Nb substitution on the crystal structure and electrochemical properties of LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} were studied systematically by X-ray diffraction (XRD) and various electrochemical measurements. The results showed Nb substitution played an important role in the good cycling performance of LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2}. Charge/discharge tests revealed that LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3–0.02}Nb{sub 0.02}O{sub 2} showed a capacity retention of 94.1% at 1 C after 50 cycles in a high cutoff voltage range (3.0–4.6 V), while discharge capacity of LiNi{sub 1/3}Co{sub 1/3}Mn{sub 1/3}O{sub 2} remains only 89.4% of that at 1 C. Ex-situ XRD analysis and EIS analysis indicated that the improved electrochemical properties of Nb-doped sample result from the more stable structure and lower resistance during the electrochemical cycling.

Tunable photovoltaic effect and solar cell performance of self-doped perovskite SrTiO3

Directory of Open Access Journals (Sweden)

K. X. Jin

2012-12-01

Full Text Available We report on the tunable photovoltaic effect of self-doped single-crystal SrTiO3 (STO, a prototypical perovskite-structured complex oxide, and evaluate its performance in Schottky junction solar cells. The photovaltaic characteristics of vacuum-reduced STO single crystals are dictated by a thin surface layer with electrons donated by oxygen vacancies. Under UV illumination, a photovoltage of 1.1 V is observed in the as-received STO single crystal, while the sample reduced at 750 °C presents the highest incident photon to carrier conversion efficiency. Furthermore, in the STO/Pt Schottky junction, a power conversion efficiency of 0.88% was achieved under standard AM 1.5 illumination at room temperature. This work establishes STO as a high-mobility photovoltaic semiconductor with potential of integration in self-powered oxide electronics.

Effects of Sb-doping on the formation of (K, Na)(Nb, Sb)O3 solid solution under hydrothermal conditions

International Nuclear Information System (INIS)

Su Likui; Zhu Kongjun; Bai Lin; Qiu Jinhao; Ji Hongli

2010-01-01

(K, Na)(Nb, Sb)O 3 (KNNS) lead-free peizoceramic powders were successfully synthesized by hydrothermal treatment at 240 o C for 8 h using the KOH, NaOH, Nb 2 O 5 and Sb 2 O 3 as raw materials. Effects of Sb-doping on the crystal structure and morphology of the as-prepared powders were investigated by powder X-ray diffraction (XRD), Raman spectra (Raman), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The Sb element was successfully doped into the alkaline niobate perovskite structure to form crystalline (K 0.7 Na 0.3 )(Nb 0.95 Sb 0.05 )O 3 lead-free piezoelectric ceramic powder, which has a hexagonal morphology due to the aggregation growth of small grains. Phase and morphology evolutions with the reaction time were also studied, and a possible formation mechanism was proposed.

Andreev Reflection Spectroscopy of Nb-doped Bi2Se3 Topological Insulator

Science.gov (United States)

Kurter, C.; Finck, A. D. K.; Qiu, Y.; Huemiller, E.; Weis, A.; Atkinson, J.; Medvedeva, J.; Hor, Y. S.; van Harlingen, D. J.

2015-03-01

Doped topological insulators are speculated to realize p-wave superconductivity with unusual low energy quasiparticles, such as surface Andreev bound states. We present point contact spectroscopy of thin exfoliated flakes of Nb-doped Bi2Se3 where superconductivity persists up to ~ 1 K, compared to 3.2 K in bulk crystals. The critical magnetic field is strongly anisotropic, consistent with quasi-2D behavior. Andreev reflection measurements of devices with low resistance contacts result in prominent BTK-like behavior with an enhanced conductance plateau at low bias. For high resistance contacts, we observe a split zero bias conductance anomaly and additional features at the superconducting gap. Our results suggest that this material is a promising platform for studying topological superconductivity. We acknowledge support from Microsoft Project Q.

Quantitative analysis of UV excitation bands for red emissions in Pr3+-doped CaTiO3, SrTiO3 and BaTiO3 phosphors by peak fitting

International Nuclear Information System (INIS)

Fujiwara, Rei; Sano, Hiroyuki; Shimizu, Mikio; Kuwabara, Makoto

2009-01-01

A quantitative spectral analysis of the ultraviolet (UV) broad excitation bands, which are located in the range 300-400 nm, for red emissions at around 610 nm in Pr-doped CaTiO 3 , SrTiO 3 :Al and BaTiO 3 :Mg phosphors has been carried out using a peak fitting technique. The obtained results demonstrate that the UV broad band of CaTiO 3 :Pr consists of four primary excitation bands centered around 330, 335, 365 and 380 nm and those of both SrTiO 3 :Al and BaTiO 3 :Mg consist of three primary bands centered around 310, 345 and 370 nm. Based on the behavior patterns and the values of the respective primary excitation bands' parameters, i.e. center gravity (λ top ), maximum height (I max ) and full-width at half-maximum (FWHM), the UV-to-red relaxation processes in these titanate phosphors can be explained to be essentially the same, except for the existence of an additional relaxation pathway via electron-trap states in CaTiO 3 :Pr, which gives a characteristic shape of its UV excitation spectrum in the wavelength range of >360 nm

Preparation and properties of visible light responsive Y3+ doped Bi5Nb3O15 photocatalysts for Ornidazole decomposition

International Nuclear Information System (INIS)

Zhao, Jie; Yao, Binghua; He, Qiang; Zhang, Ting

2012-01-01

Highlights: ► A novel Y 3+ -Bi 5 Nb 3 O 15 material was prepared. ► Y 3+ -Bi 5 Nb 3 O 15 is firstly used for the photocatalytic degradation of Ornidazole. ► Possible pathway of Ornidazole degradation in aqueous solution is proposed. - Abstract: Nanoparticle of Bi 5 Nb 3 O 15 doped with Y 3+ was prepared for the first time by the sol–gel method combined with impregnation. The degradation of Ornidazole reacting with Y 3+ -Bi 5 Nb 3 O 15 was investigated to explore the feasibility of using Y 3+ -Bi 5 Nb 3 O 15 to treat antibiotics in wastewater. The products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, UV–vis diffuse reflectance spectrum and X-ray photoelectron spectroscopy. The results showed that the Y 3+ -Bi 5 Nb 3 O 15 exhibited single-crystalline orthorhombic structure with small particle size (20–100 nm); additionally, its UV–vis absorbance edges significantly shift to the visible-light region. The as-prepared nanoparticles exhibited a high photocatalytic activity in the decomposition of Ornidazole and several possible pathways of degradation of Ornidazole were proposed according to the results of ultra-performance liquid chromatography tandem mass spectrometry.

The effect of Mg doping on the Raman spectra of LiNbO3 crystals

International Nuclear Information System (INIS)

Lengyel, K.; Kovacs, L.; Peter, A.; Polgar, K.; Corradi, G.; Bourson, P.

2007-01-01

LiNbO 3 :Mg crystals doped with 0-8 mol% Mg with stoichiometric, intermediate and congruent compositions were systematically investigated by Raman spectroscopy in backscattering y(zx)y and y(zz)y geometries. The halfwidths of E(TO 3 ) - E(TO 9 ) and A 1 (TO 1 ) - A 1 (TO 4 ) bands, which have a significant composition dependence for undoped LiNbO 3 crystals, show only weak Mg-concentration dependence below the photorefractive threshold. This is a consequence of the counteracting effect of the decreasing amount of Nb ions at Li-ion sites (Nb Li ) and increasing amount of Mg ions at Li-ion sites (Mg Li ). The halfwidths of these bands, however, increase linearly with growing Mg content for samples above the threshold, irrespective of the Li/Nb ratio. The same effect was observed in the Mg dependence of the position and halfwidth of the two-phonon band at about 689 - 705 cm -1 . The change in the Mg concentration dependence of these parameters at a given Li/Nb ratio determines the same threshold value as that concluded from IR and UV spectroscopic measurements. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Electric-field gradients at the $^{111}In$ and $^{111m}Cd$ sites in undoped and Mg-doped $LiNbO_{3}$

CERN Document Server

Hauer, B; Marques, J G; Barradas, N P; Correia, J G; Agulló-López, F; Diéguez, E

1995-01-01

The quadrupole interaction of 111Cd in undoped (congruent) and Mg-doped LiNbO3 single crystals has been studied using the perturbed angular correlation technique after implantation of 111In and 111mCd. A stepwise-annealing procedure shows the lattice to be fully reconstructed at 773 K. Our results show that both In and Cd are in the Li position. Mg doping at 6 mol % does not have any effect on the lattice location of these impurities in LiNbO3.

Effect of MnO doping on the structure, microstructure and electrical properties of the (K,Na,Li)(Nb,Ta,Sb)O3 lead-free piezoceramics

International Nuclear Information System (INIS)

Rubio-Marcos, F.; Marchet, P.; Vendrell, X.; Romero, J.J.; Remondiere, F.; Mestres, L.; Fernandez, J.F.

2011-01-01

Highlights: · MnO doping effects on structure and properties of (K,Na,Li)(Nb,Ta,Sb)O 3 piezoceramics. · The structure changes towards an orthorhombic symmetry for higher MnO concentrations. · High doping levels induce a tetragonal tungsten-bronze secondary phase. · Mn 2+ doping modifies the phase transition temperature and the piezoelectric properties. · Manganese doping increases the mechanical quality factor Q m . - Abstract: Mn 2+ -doped (K,Na,Li)(Nb,Ta,Sb)O 3 lead-free piezoelectric ceramics have been prepared by a conventional sintering technique. The effects of Mn 2+ doping on the phase structure, microstructure and ferro-piezoelectric properties of the ceramics have been evaluated. MnO doping modifies the (K,Na,Li)(Nb,Ta,Sb)O 3 structure, giving rise to the appearance of a TTB-like secondary phase and to changes on the orthorhombic to tetragonal phase transition temperature. The modification of this temperature induces a reduction of the piezoelectric constants, which is accompanied by an increase on the mechanical quality factor. Mn 2+ ions incorporate into the perovskite structure in different off ways depending on their concentration.

Textured and tungsten-bronze-niobate-doped (K,Na,Li)(Nb,Ta)O3 piezoceramic materials

International Nuclear Information System (INIS)

Soller, Thomas; Bathelt, Robert; Benkert, Katrin; Bodinger, Hermann; Schuh, Carsten; Schlenkrich, Falko

2010-01-01

In this study, the effects of an alkaline-earth niobate doping in tungsten-bronze (TB) stoichiometry on the piezoelectric properties and the phase transition temperatures of lead-free (K,Na,Li)(Nb,Ta)O 3 ceramics were investigated. In particular, the TB compounds barium niobate (BN), barium sodium niobate (BNN) and strontium calcium sodium niobate (SCNN) were investigated. The TB-modified ceramics show promising piezoelectric properties with large-signal piezo coefficients, d 33 * lose to 400 pm/V, planar coupling coefficients, k p , up to 0.45 and Curie temperatures of approximately 310 .deg. C. In addition, the effect of texturing on the undoped (K,Na,Li)(Nb,Ta)O 3 base composition via templated grain growth (TGG) with microcrystalline NaNbO 3 templates was examined. Lotgering factors up to 81% and strain enhancements by a factor 1.5 with large-signal values of d 33 * up to 550 pm/V could be achieved in the textured samples.

Evolution of ferromagnetism in two-dimensional electron gas of LaTiO3/SrTiO3

Science.gov (United States)

Wen, Fangdi; Cao, Yanwei; Liu, Xiaoran; Pal, B.; Middey, S.; Kareev, M.; Chakhalian, J.

2018-03-01

Understanding, creating, and manipulating spin polarization of two-dimensional electron gases at complex oxide interfaces present an experimental challenge. For example, despite almost a decade long research effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3 heterojunctions is still an open question. Here, by using a prototypical two-dimensional electron gas (2DEG) which emerges at the interface between band insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3, the experiment reveals the evidence for magnetic phase separation in a hole-doped Ti d1 t2g system, resulting in spin-polarized 2DEG. The details of electronic and magnetic properties of the 2DEG were investigated by temperature-dependent d.c. transport, angle-dependent X-ray photoemission spectroscopy, and temperature-dependent magnetoresistance. The observation of clear hysteresis in magnetotransport at low magnetic fields implies spin-polarization from magnetic islands in the hole rich LaTiO3 near the interface. These findings emphasize the role of magnetic instabilities in doped Mott insulators, thus providing another path for designing all-oxide structures relevant to spintronic applications.

Synthesis of Nb-doped SrTiO₃ by a modified glycine-nitrate process

DEFF Research Database (Denmark)

Blennow Tullmar, Peter; Kammer Hansen, Kent; Wallenberg, L.R.

2007-01-01

The objective of the present investigation was to develop a technique to synthesize submicronic particles of Nb-doped strontium titanate with a homogeneous composition. This was achieved by a modified glycine-nitrate process, using Ti-lactate, Nb-oxalate, and Sr(NO3)(2) as starting materials....... A combination of both citric acid and glycine was needed in order to integrate the useful features of both complexation and combustion natures of citric acid and glycine, respectively. The amount of citric acid, glycine, and nitrates in the starting solution, as well as the source for extra nitrates...

Piezoelectric properties and temperature stability of Mn-doped Pb(Mg1/3Nb2/3)-PbZrO3-PbTiO3 textured ceramics

OpenAIRE

Yan, Yongke; Cho, Kyung-Hoon; Priya, Shashank

2012-01-01

In this letter, we report the electromechanical properties of textured 0.4Pb(Mg1/3Nb2/3) O-3-0.25PbZrO(3)-0.35PbTiO(3) (PMN-PZT) composition which has relatively high rhombohedral to tetragonal (R-T) transition temperature (TR-T of 160 degrees C) and Curie temperature (T-C of 234 degrees C) and explore the effect of Mn-doping on this composition. It was found that MnO2-doped textured PMN-PZT ceramics with 5 vol.% BaTiO3 template (T-5BT) exhibited inferior temperature stability. The coupling f...

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.

Electrical properties of Sb and Cr-doped PbZrO3-PbTiO3-PbMg1/3Nb2/3O3 ceramics

OpenAIRE

Whatmore, Roger W.; Molter, O.; Shaw, Christopher P.

2003-01-01

The pyroelectric, dielectric and DC resistive properties of Sb and Cr-doped ceramics with a base composition of Pb(Mg1/3Nb2/3)0.025(Zr0.825Ti0.175)0.975O3 have been studied. Sb doping has been shown to produce a linear reduction in Curie temperature (TC=−22z+294 °C) with concentration (z) and to give an increase in pyroelectric coefficient from 250 to 310 μCm−2 K−1 for z increasing from 0 to 3 at.%. It also produces first a reduction and then an increase in both dielectric constant and loss, ...

Spin injection and detection in lanthanum- and niobium-doped SrTiO3 using the Hanle technique

KAUST Repository

Han, Wei

2013-07-08

There has been much interest in the injection and detection of spin-polarized carriers in semiconductors for the purposes of developing novel spintronic devices. Here we report the electrical injection and detection of spin-polarized carriers into Nb-doped strontium titanate single crystals and La-doped strontium titanate epitaxial thin films using MgO tunnel barriers and the three-terminal Hanle technique. Spin lifetimes of up to ∼100 ps are measured at room temperature and vary little as the temperature is decreased to low temperatures. However, the mobility of the strontium titanate has a strong temperature dependence. This behaviour and the carrier doping dependence of the spin lifetime suggest that the spin lifetime is limited by spin-dependent scattering at the MgO/strontium titanate interfaces, perhaps related to the formation of doping induced Ti 3+. Our results reveal a severe limitation of the three-terminal Hanle technique for measuring spin lifetimes within the interior of the subject material. © 2013 Macmillan Publishers Limited. All rights reserved.

Steps in growth of Nb-doped layered titanates with very high surface area suitable for water purification

International Nuclear Information System (INIS)

Milanović, Marija; Nikolić, Ljubica M.; Stijepović, Ivan; Kontos, Athanassios G.; Giannakopoulos, Konstantinos P.

2014-01-01

Nb-doped layered titanates, as highly efficient adsorbents, have been synthesized by hydrothermal reaction for variable duration and at 150 °C in a highly alkaline solution with NbCl 5 as the Nb source. The results have shown the formation of nanosheets already after 1 h of hydrothermal processing, but morphology and phase composition change as the reaction proceeds. The prepared layered titanates have been structurally investigated via scanning and transmission electron microscopy, X-ray diffraction, as well as Raman and Fourier transform infrared spectroscopies. The steps of layered titanate growth have been followed and an intermediate layered anatase phase is identified. Thus optimized growth of mesoporous titanate materials with 10% Nb atomic content present very high specific surface area of 345.3 m 2  g −1 , and perform as very efficient adsorbents for wastewater treatment applications. - Highlights: • Nb-doped layered titanates have been prepared by a hydrothermal procedure. • Introduction of Nb to precursor lowers the rate of layered titanate formation. • Steps in growth of Nb-doped layered titanates are considered. • Nb-doped layered titanates show high/fast MB adsorption from concentrated solution

Mechanism of luminescent enhancement in Ba{sub 2}GdNbO{sub 6}:Eu{sup 3+} perovskite by Li{sup +} co-doping

Energy Technology Data Exchange (ETDEWEB)

Rezende, Marcos Vinicius dos Santos [Departamento de Física, Universidade Federal de Sergipe, 49500-000, Itabaiana, SE (Brazil); Valério, Mario Ernesto Giroldo [Departamento de Física, Universidade Federal de Sergipe, 49100-000 São Cristóvão, SE (Brazil); Mouta, Rodolpho; Diniz, Eduardo Moraes [Departamento de Física, CCET, Universidade Federal do Maranhão, 65085-580 São Luís, MA (Brazil); Paschoal, Carlos William de Araujo, E-mail: paschoal@ufma.br [Departamento de Física, CCET, Universidade Federal do Maranhão, 65085-580 São Luís, MA (Brazil); Department of Materials Science and Engineering, University of California Berkeley, 94720-1760 Berkeley, CA (United States); Department of Physics, University of California Berkeley, 94720-7300 Berkeley, CA (United States)

2015-02-15

We investigated the Li{sup +} ion incorporation in Ba{sub 2}GdNbO{sub 6}:Eu{sup 3+} perovskite by atomistic simulations based on energy minimization. We predicted the most probable sites occupied by Eu{sup 3+} and Li{sup +} ions and the related charge-compensation mechanisms involved into these substitutions. The results show that the Eu{sup 3+} and Li{sup +} ions are incorporated mainly at the Gd{sup 3+} site. In the Li{sup +} ion case, there is a charge compensation by Nb{sub Gd}{sup •} {sup •} antisite. The crystal field parameters and the transition levels for the Eu{sup 3+} ion in the BGN:Eu{sup 3+} were calculated with basis on the simulated local symmetry of the Eu{sup 3+} site. The results show that the mechanism of luminescent properties enhancement is the symmetry distortion induced by the Li{sup +} co-doping. - Highlights: • We performed a full defect calculations in Ba{sub 2}GdNbO{sub 6} double perovskite. • We modeled with excellent agreement the optical transition of Ba{sub 2}GdNbO{sub 6}:Eu{sup 3+} crystal. • We explained the mechanism of luminescent enhancement in Ba{sub 2}GdNbO{sub 6}:Eu{sup 3+} perovskite by Li{sup +} co-doping.

Z-contrast imaging of ordered structures in Pb(Mg1/3Nb2/3)O3 and Ba(Mg1/3Nb2/3)O3

International Nuclear Information System (INIS)

Yan, Y.; Pennycook, S.J.; Xu, Z.; Viehland, D.

1998-02-01

Lead-based cubic perovskites such as Pb(B 1/3 2+ B 2/3 5+ )O 3 (B 2+ Mg, Co, Ni, Zn; B 5+ = Nb, Ta) are relaxor ferroelectrics. Localized order and disorder often occur in materials of this type. In the Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) family, previous studies have proposed two models, space-charge and charge-balance models. In the first model, the ordered regions carry a net negative charge [Pb(Mg 1/2 Nb 1/2 )O 3 ], while in the second model it does not carry a net charge [Pb((Mg 2/3 Nb 1/3 ) 1/2 Nb 1/2 )O 3 ]. However, no direct evidence for these two models has appeared in the literature yet. In this paper the authors report the first direct observations of local ordering in undoped and La-doped Pb(Mg 1/3 Nb 2/3 )O 3 , using high-resolution Z-contrast imaging. Because the ordered structure in Ba(Mg 1/3 Nb 2/3 )O 3 is well known, the Z-contrast image from an ordered domain is used as a reference for this study

Effect of MnO doping on the structure, microstructure and electrical properties of the (K,Na,Li)(Nb,Ta,Sb)O{sub 3} lead-free piezoceramics

Energy Technology Data Exchange (ETDEWEB)

Rubio-Marcos, F., E-mail: fernando.rubio-marcos@unilim.fr [Laboratoire de Science des Procedes Ceramiques et de Traitements de Surface, UMR 6638 CNRS, Universite de Limoges, Centre Europeen de la Ceramique, 12, rue Atlantis, 87068 Limoges Cedex (France); Marchet, P. [Laboratoire de Science des Procedes Ceramiques et de Traitements de Surface, UMR 6638 CNRS, Universite de Limoges, Centre Europeen de la Ceramique, 12, rue Atlantis, 87068 Limoges Cedex (France); Vendrell, X. [Grup de Quimica de l' Estat Solid, Departament de Quimica Inorganica, Universitat de Barcelona, 08028 Barcelona (Spain); Romero, J.J. [Electroceramic Department, Instituto de Ceramica y Vidrio, CSIC, Kelsen 5, 28049 Madrid (Spain); Remondiere, F. [Laboratoire de Science des Procedes Ceramiques et de Traitements de Surface, UMR 6638 CNRS, Universite de Limoges, Centre Europeen de la Ceramique, 12, rue Atlantis, 87068 Limoges Cedex (France); Mestres, L. [Grup de Quimica de l' Estat Solid, Departament de Quimica Inorganica, Universitat de Barcelona, 08028 Barcelona (Spain); Fernandez, J.F. [Electroceramic Department, Instituto de Ceramica y Vidrio, CSIC, Kelsen 5, 28049 Madrid (Spain)

2011-09-01

Highlights: {center_dot} MnO doping effects on structure and properties of (K,Na,Li)(Nb,Ta,Sb)O{sub 3} piezoceramics. {center_dot} The structure changes towards an orthorhombic symmetry for higher MnO concentrations. {center_dot} High doping levels induce a tetragonal tungsten-bronze secondary phase. {center_dot} Mn{sup 2+} doping modifies the phase transition temperature and the piezoelectric properties. {center_dot} Manganese doping increases the mechanical quality factor Q{sub m}. - Abstract: Mn{sup 2+}-doped (K,Na,Li)(Nb,Ta,Sb)O{sub 3} lead-free piezoelectric ceramics have been prepared by a conventional sintering technique. The effects of Mn{sup 2+} doping on the phase structure, microstructure and ferro-piezoelectric properties of the ceramics have been evaluated. MnO doping modifies the (K,Na,Li)(Nb,Ta,Sb)O{sub 3} structure, giving rise to the appearance of a TTB-like secondary phase and to changes on the orthorhombic to tetragonal phase transition temperature. The modification of this temperature induces a reduction of the piezoelectric constants, which is accompanied by an increase on the mechanical quality factor. Mn{sup 2+} ions incorporate into the perovskite structure in different off ways depending on their concentration.

Combined ion beam and hyperfine interaction studies of LiNbO3 single crystals

International Nuclear Information System (INIS)

Marques, J.G.; Kling, A.; Soares, J.C.; Rebouta, L.

1999-01-01

A review of recent studies of LiNbO 3 crystals doped with Hf and Mg,Hf combining high precision RBS/channelling, PIXE/channelling and hyperfine interaction techniques is presented. The lattice location of Hf was found to depend strongly on the dopant concentration, crystal stoichiometry and Mg co-doping level. At low concentrations Hf occupies Li sites in congruent crystals, while it occupies both Li and Nb sites for higher doping levels or in near-stoichiometric crystals. Co-doping with Mg also forces a split location of Hf in Li and Nb sites and when the MgO amount exceeds 4.5 mol% Hf occupies only Nb sites. Neutron irradiation of these crystals displaces Hf from its initial lattice site and leads to a strong decrease of the Nb site fraction. The results are discussed in the framework of the Li and Nb vacancy models currently proposed in the literature for the defect structure of LiNbO 3 . (author)

Nb-doped TiO2 thin films as photocatalytic materials

Indian Academy of Sciences (India)

Administrator

that hydrophilicity is ruled by a different mechanism than photocatalysis. Keywords. Nb-doped ... studied for a large area of applications: solar cells,1–3 hydrogen ... our previous work.12,13 Results show that all the films are amorphous and ...

The metallic interface between the two band insulators LaGaO3 and SrTiO3

KAUST Repository

Nazir, Safdar; Schwingenschlö gl, Udo; Singh, Nirpendra

2011-01-01

The formation of metallic interface states between the two band insulators LaGaO3 and SrTiO3 is studied by the full-potential linearized augmented plane-wave method based on density functional theory.Structural optimization of the atomic positions points to only small changes of the chemical bonding at the interface. The n-type (LaO/TiO2) and p-type (GaO2/SrO) interfaces turn out to be metallic. Reduction of the O content increases the conductivity of the n-type interface, while the p-type interface can be turned gradually from a hole doped into an electron doped state.

The metallic interface between the two band insulators LaGaO3 and SrTiO3

KAUST Repository

Nazir, Safdar

2011-06-28

The formation of metallic interface states between the two band insulators LaGaO3 and SrTiO3 is studied by the full-potential linearized augmented plane-wave method based on density functional theory.Structural optimization of the atomic positions points to only small changes of the chemical bonding at the interface. The n-type (LaO/TiO2) and p-type (GaO2/SrO) interfaces turn out to be metallic. Reduction of the O content increases the conductivity of the n-type interface, while the p-type interface can be turned gradually from a hole doped into an electron doped state.

Electrical transport across nanometric SrTiO3 and BaTiO3 barriers in conducting/insulator/conducting junctions

Science.gov (United States)

Navarro, H.; Sirena, M.; González Sutter, J.; Troiani, H. E.; del Corro, P. G.; Granell, P.; Golmar, F.; Haberkorn, N.

2018-01-01

We report the electrical transport properties of conducting/insulator/conducting heterostructures by studying current-voltage IV curves at room temperature. The measurements were obtained on tunnel junctions with different areas (900, 400 and 100 μm2) using a conducting atomic force microscope. Trilayers with GdBa2Cu3O7 (GBCO) as the bottom electrode, SrTiO3 or BaTiO3 (thicknesses between 1.6 and 4 nm) as the insulator barrier, and GBCO or Nb as the top electrode were grown by DC sputtering on (100) SrTiO3 substrates For SrTiO3 and BaTiO3 barriers, asymmetric IV curves at positive and negative polarization can be obtained using electrodes with different work function. In addition, hysteretic IV curves are obtained for BaTiO3 barriers, which can be ascribed to a combined effect of the FE reversal switching polarization and an oxygen vacancy migration. For GBCO/BaTiO3/GBCO heterostructures, the IV curves correspond to that expected for asymmetric interfaces, which indicates that the disorder affects differently the properties at the bottom and top interfaces. Our results show the role of the interface disorder on the electrical transport of conducting/insulator/conduction heterostructures, which is relevant for different applications, going from resistive switching memories (at room temperature) to Josephson junctions (at low temperatures).

Tuning electronic structure and optical properties of SrTiO{sub 3} by site-specific doping by Nb with N/B from hybrid functional calculations

Energy Technology Data Exchange (ETDEWEB)

Liu, Yanyu; Zhou, Wei; Wu, Ping, E-mail: pingwu@tju.edu.cn

2017-07-01

In this study, the extensive density functional theory calculations are performed to modify the electronic structure of perovskite SrTiO{sub 3} by doping with Nb and N/B. The unoccupied states induced by the Nb monodoping at the Sr or Ti site, which were passivated in the codoped systems (the substitution of Nb at Ti site with the replacement of N at O site: Nb@Ti/N@O and the substitution of Nb at Sr site with the replacement of B at O site: Nb@Sr/B@O). The charge-compensated donor-acceptor pair codoping creates the new occupied states within the band gap, which yields the absorption edge extend to visible light. And the calculated defect formation energy implies that the codoped systems are energetically favorable under the O-rich condition. Moreover, the band-edge alignment confirmed that the Nb@Ti/N@O system is desirable for the spontaneous water splitting under visible light and the Nb@Sr/B@O system can split water into hydrogen in presence of sacrificial agent. - Highlights: • A systematical study has been employed on SrTiO{sub 3} with the donor-acceptor codoping. • The donor-acceptor pair codoping yields the absorption edge extend to visible light. • The formation energy implies that the codoped systems are favorable under the O-rich condition. • The Nb@Ti/N@O system is desirable for the spontaneous water splitting under visible light. • The Nb@Sr/B@O system can split water into hydrogen in presence of sacrificial agent.

Effects of B site doping on electronic structures of InNbO4 based on hybrid density functional calculations

Science.gov (United States)

Lu, M. F.; Zhou, C. P.; Li, Q. Q.; Zhang, C. L.; Shi, H. F.

2018-01-01

In order to improve the photocatalytic activity under visible-light irradiation, we adopted first principle calculations based on density functional theory (DFT) to calculate the electronic structures of B site transition metal element doped InNbO4. The results indicated that the complete hybridization of Nb 4d states and some Ti 3d states contributed to the new conduction band of Ti doped InNbO4, barely changing the position of band edge. For Cr doping, some localized Cr 3d states were introduced into the band gap. Nonetheless, the potential of localized levels was too positive to cause visible-light reaction. When it came to Cu doping, the band gap was almost same with that of InNbO4 as well as some localized Cu 3d states appeared above the top of VB. The introduction of localized energy levels benefited electrons to migrate from valence band (VB) to conduction band (CB) by absorbing lower energy photons, realizing visible-light response.

Host-Sensitized and Tunable Luminescence of GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) Nanocrystalline Phosphors with Abundant Color.

Science.gov (United States)

Liu, Xiaoming; Chen, Chen; Li, Shuailong; Dai, Yuhua; Guo, Huiqin; Tang, Xinghua; Xie, Yu; Yan, Liushui

2016-10-17

Up to now, GdNbO 4 has always been regarded as an essentially inert material in the visible region with excitation of UV light and electron beams. Nevertheless, here we demonstrate a new recreating blue emission of GdNbO 4 nanocrystalline phosphors with a quantum efficiency of 41.6% and host sensitized luminescence in GdNbO 4 :Ln 3+ (Ln 3+ = Eu 3+ /Tb 3+ /Tm 3+ ) nanocrystalline phosphors with abundant color in response to UV light and electron beams. The GdNbO 4 and GdNbO 4 :Ln 3+ (Ln 3+ = Eu 3+ /Tb 3+ /Tm 3+ ) nanocrystalline phosphors were synthesized by a Pechini-type sol-gel process. With excitation of UV light and low-voltage electron beams, the obtained GdNbO 4 nanocrystalline phosphor presents a strong blue luminescence from 280 to 650 nm centered around 440 nm, and the GdNbO 4 :Ln 3+ nanocrystalline phosphors show both host emission and respective emission lines derived from the characterize f-f transitions of the doping Eu 3+ , Tb 3+ , and Tm 3+ ions. The luminescence color of GdNbO 4 :Ln 3+ nanocrystalline phosphors can be tuned from blue to green, red, blue-green, orange, pinkish, white, etc. by varying the doping species, concentration, and relative ratio of the codoping rare earth ions in GdNbO 4 host lattice. A single-phase white-light-emission has been realized in Eu 3+ /Tb 3+ /Tm 3+ triply doped GdNbO 4 nanocrystalline phosphors. The luminescence properties and mechanisms of GdNbO 4 and GdNbO 4 :Ln 3+ (Ln 3+ = Eu 3+ /Tb 3+ /Tm 3+ ) are updated.

A versatile light-switchable nanorod memory: Wurtzite ZnO on perovskite SrTiO3

KAUST Repository

Kumar, Anup Bera

2013-04-25

Integrating materials with distinct lattice symmetries and dimensions is an effective design strategy toward realizing novel devices with unprecedented functionalities, but many challenges remain in synthesis and device design. Here, a heterojunction memory made of wurtzite ZnO nanorods grown on perovskite Nb-doped SrTiO3 (NSTO) is reported, the electronic properties of which can be drastically reconfigured by applying a voltage and light. Despite of the distinct lattice structures of ZnO and NSTO, a consistent nature of single crystallinity is achieved in the heterojunctions via the low-temperature solution-based hydrothermal growth. In addition to a high and persistent photoconductivity, the ZnO/NSTO heterojunction diode can be turned into a versatile light-switchable resistive switching memory with highly tunable ON and OFF states. The reversible modification of the effective interfacial energy barrier in the concurrent electronic and ionic processes most likely gives rise to the high susceptibility of the ZnO/NSTO heterojunction to external electric and optical stimuli. Furthermore, this facile synthesis route is promising to be generalized to other novel functional nanodevices integrating materials with diverse structures and properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Growth and giant coercive field of spinel-structured Co3- x Mn x O4 thin films

Science.gov (United States)

Kwak, Yongsu; Song, Jonghyun; Koo, Taeyeong

2016-08-01

We grew epitaxial thin films of CoMn2O4 and Co2MnO4 on Nb-doped SrTiO3(011) and SrTiO3(001) single crystal substrates using pulsed laser deposition. The magnetic Curie temperature ( T c ) of the Co2MnO4 thin films was ~176 K, which is higher than that of the bulk whereas CoMn2O4 thin films exhibited a value of T c (~151 K) lower than that of the bulk. For the Co2MnO4 thin films, the M - H loop showed a coercive field of ~0.7 T at 10 K, similar to the value for the bulk. However, the M -H loop of the CoMn2O4(0 ll) thin film grown on a Nb-doped SrTiO3(011) substrate exhibited a coercive field of ~4.5 T at 30 K, which is significantly higher than those of the Co2MnO4 thin film and bulk. This giant coercive field, only observed for the CoMn2O4(0 ll) thin film, can be attributed to the shape anisotropy and strong spin-orbit coupling.

Microstructure and electric characteristics of AETiO3 (AE=Mg, Ca, Sr doped CaCu3Ti4O12 thin films prepared by the sol–gel method

Directory of Open Access Journals (Sweden)

Dong Xu

2015-10-01

Full Text Available This paper focuses on the effects of alkline-earth metal titante AETiO3 (AE=Mg, Ca, Sr doping on the microstructure and electric characteristics of CaCu3Ti4O12 thin films prepared by the sol–gel method. The results showed that the grain size of CCTO thin films could be increased by MgTiO3 doping. The movement of the grain boundaries was impeded by the second phases of CaTiO3 and SrTiO3 concentrating at grain boundaries in CaTiO3 and SrTiO3 doped CCTO thin films. Rapid ascent of dielectric constant could be observed in 0.1Mg TiO3 doped CCTO thin films, which was almost as three times high as pure CCTO thin film and the descent of the dielectric loss at low frequency could also be observed. In addition, the nonlinear coefficient (α, threshold voltage (VT and leakage current (IL of AETiO3 doped CCTO thin films (AE=Mg, Ca, Sr showed different variation with the increasing content of the MgTiO3, CaTiO3 and SrTiO3.

Electromagnetic and optical characteristics of Nb5+-doped double-crossover and salmon DNA thin films

Science.gov (United States)

Babu Mitta, Sekhar; Reddy Dugasani, Sreekantha; Jung, Soon-Gil; Vellampatti, Srivithya; Park, Tuson; Park, Sung Ha

2017-10-01

We report the fabrication and physical characteristics of niobium ion (Nb5+)-doped double-crossover DNA (DX-DNA) and salmon DNA (SDNA) thin films. Different concentrations of Nb5+ ([Nb5+]) are coordinated into the DNA molecules, and the thin films are fabricated via substrate-assisted growth (DX-DNA) and drop-casting (SDNA) on oxygen plasma treated substrates. We conducted atomic force microscopy to estimate the optimum concentration of Nb5+ ([Nb5+]O = 0.08 mM) in Nb5+-doped DX-DNA thin films, up to which the DX-DNA lattices maintain their structures without deformation. X-ray photoelectron spectroscopy (XPS) was performed to probe the chemical nature of the intercalated Nb5+ in the SDNA thin films. The change in peak intensities and the shift in binding energy were witnessed in XPS spectra to explicate the binding and charge transfer mechanisms between Nb5+ and SDNA molecules. UV-visible, Raman, and photoluminescence (PL) spectra were measured to determine the optical properties and thus investigate the binding modes, Nb5+ coordination sites in Nb5+-doped SDNA thin films, and energy transfer mechanisms, respectively. As [Nb5+] increases, the absorbance peak intensities monotonically increase until ˜[Nb5+]O and then decrease. However, from the Raman measurements, the peak intensities gradually decrease with an increase in [Nb5+] to reveal the binding mechanism and binding sites of metal ions in the SDNA molecules. From the PL, we observe the emission intensities to reduce them at up to ˜[Nb5+]O and then increase after that, expecting the energy transfer between the Nb5+ and SDNA molecules. The current-voltage measurement shows a significant increase in the current observed as [Nb5+] increases in the SDNA thin films when compared to that of pristine SDNA thin films. Finally, we investigate the temperature dependent magnetization in which the Nb5+-doped SDNA thin films reveal weak ferromagnetism due to the existence of tiny magnetic dipoles in the Nb5+-doped SDNA

Nonlinear optical properties of TeO2-P2 O5- ZnO-LiNbO3 glass doped with Er3+ ions

Science.gov (United States)

Miedzinski, R.; Fuks-Janczarek, I.; El Sayed Said, Y.

2016-10-01

A series of lithium niobate LiNbO3 (LN) single crystals doped with Er3+ were grown under the same conditions by melt-quenching method. The distribution coefficients of rare-earth (RE) elements in the "crystal-melt" system of LN were determined at the beginning of the crystal growth. Their dependence on the dopant concentration in melt for 0.4 and 0.8 wt % was investigated. The procedure is applied to RE-doped lithium niobate (LiNbO3), a material of great interest for optoelectronic applications. We have obtained the real χR(3) and imaginary parts χI(3) of the third-order, nonlinear optical susceptibility to the nonlinear refractive index n2 and the nonlinear absorption coefficient β that are valid for absorbing systems. We show that nonlinear refractive or absorptive effects are the consequence of the interplay between the real and imaginary parts of the third-order susceptibilities of the materials. The method for measuring non-linear absorption coefficients and nonlinear refractive index based on well-known Z-scan is presented.

Effect of Nb doping on the structural, morphological, optical and electrical properties of RF magnetron sputtered In{sub 2}O{sub 3} nanostructured films

Energy Technology Data Exchange (ETDEWEB)

Reshmi Krishnan, R.; Chalana, S.R.; Suresh, S.; Sudheer, S.K.; Mahadevan Pillai, V.P. [Department of Optoelectronics, University of Kerala (India); Sudarsanakumar, C. [School of Pure and Applied Physics, Mahatma Gandhi University, Kerala (India); Santhosh Kumar, M.C. [Optoelectronic Materials and Devices Lab, Department of Physics, National Institute of Technology, Tiruchirappalli (India)

2017-01-15

Undoped and niobium (Nb) doped indium oxide (In{sub 2}O{sub 3}) thin films are prepared by radio frequency magnetron sputtering technique. The effect of Nb on the structural, morphological, optical and electrical properties of In{sub 2}O{sub 3}films are analyzed using techniques such as X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy, UV-visible spectroscopy, spectroscopic ellipsometry, photoluminescence spectroscopy and Hall effect measurements. XRD analysis reveals that the as-deposited undoped and Nb doped films are polycrystalline in nature with cubic bixbyite structure. Raman analysis supports the presence of cubic bixbyite structure of In{sub 2}O{sub 3}in the films. XPS analysis shows a decrease of oxygen deficiency due to Nb and the existence of Nb as Nb{sup 4+} in the In{sub 2}O{sub 3}lattice. The band gap energy of the films increases with increase in Nb concentration. PL spectra reveal intense UV and visible emissions in all the films. Optical constants of the films are determined using spectroscopic ellipsometry. The thickness of films estimated using FESEM and ellipsometry are in good agreement. The carrier concentration, mobility and nature of carriers are measured using Hall measurement technique in Van der Pauw configuration at room temperature. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

How Correlated is the FeSe /SrTiO3 System?

Science.gov (United States)

Mandal, Subhasish; Zhang, Peng; Ismail-Beigi, Sohrab; Haule, K.

2017-08-01

Recent observation of ˜10 times higher critical temperature in a FeSe monolayer compared with its bulk phase has drawn a great deal of attention because the electronic structure in the monolayer phase appears to be different than bulk FeSe. Using a combination of density functional theory and dynamical mean field theory, we find electronic correlations have important effects on the predicted atomic-scale geometry and the electronic structure of the monolayer FeSe on SrTiO3 . The electronic correlations are dominantly controlled by the Se-Fe-Se angle either in the bulk phase or the monolayer phase. But the angle sensitivity increases and the orbital differentiation decreases in the monolayer phase compared to the bulk phase. The correlations are more dependent on Hund's J than Hubbard U . The observed orbital selective incoherence to coherence crossover with temperature confirms the Hund's metallic nature of the monolayer FeSe. We also find electron doping by oxygen vacancies in SrTiO3 increases the correlation strength, especially in the dx y orbital by reducing the Se-Fe-Se angle.

Electron transport investigation of layered MoO3 oxides doped with different concentrations of Nb2O5 oxide

International Nuclear Information System (INIS)

Al-Khawaja, S.; Kasem, M.

2008-07-01

The dc and ac electric conductivity has been studied for numerous samples of molybdenum oxide MoO 3 doped with niobium oxide Nb 2 O 5 elaborated via the solid state reactions. By means of the electric resistivity and dielectricity curves obtained as a function of temperature, and according to the dopant concentration, the behaviour of these compounds has been allocated. Most of the investigated samples, which are insulating at room temperature, have been witnessed to exhibit simultaneously two different electric comportments; metallic and semiconducting within the range of low and high temperatures respectively, designated by a critical temperature related to the nature of the material. Both of these behaviours are attributed electronically to ionic conduction mechanism, occurring in the solid material formed upon doping with Nb 2 O 5 , which is utterly diffused into the layered structure of MoO 3 particularly for x≥40% concentrations and accompanied by relaxation in the dielectric function between 5 Hz and 13 M Hz.(Authors)

Vertically aligned nitrogen doped (Sn,Nb)O_2 nanotubes – Robust photoanodes for hydrogen generation by photoelectrochemical water splitting

International Nuclear Information System (INIS)

Patel, Prasad Prakash; Hanumantha, Prashanth Jampani; Velikokhatnyi, Oleg I.; Datta, Moni Kanchan; Gattu, Bharat; Poston, James A.; Manivannan, Ayyakkannu; Kumta, Prashant N.

2016-01-01

Graphical abstract: - Highlights: • Nb and N co-doping provides excellent optoelectronic properties for SnO_2 NTs. • The optoelectronic properties of doped SnO_2 are studied by first principles study. • (Sn_0_._9_5Nb_0_._0_5)O_2:N-600 NTs exhibits superior ABPE (4.1%) to date. • Excellent photoelectrochemical stability of (Sn_0_._9_5Nb_0_._0_5)O_2:N-600 NTs. - Abstract: Hydrogen generation from photoelectrochemical (PEC) water splitting is on the forefront of clean energy generation landscape. The efficiency of PEC system is dependent on the engineering of semiconductors with tailored narrow band gap coupled with superior photoelectrochemical activity and desired stability vital for the commercialization of PEC water splitting cells. We report herein the study of vertically aligned Nb and N doped SnO_2 nanotubes (NTs), i.e., (Sn_0_._9_5Nb_0_._0_5)O_2:N NTs for PEC water splitting. (Sn_0_._9_5Nb_0_._0_5)O_2 NTs was selected for co-doping with nitrogen by systematic analysis of applied bias photon-to-current efficiency of various Nb doped SnO_2 (x = 0–0.1) compositions. Consequently, excellent photoelectrochemical stability and the highest efficiency of 4.1% is obtained for (Sn_0_._9_5Nb_0_._0_5)O_2:N-600 NTs never observed for other known TiO_2, ZnO, and Fe_2O_3 systems to date. Additionally, theoretical first principles study provides understanding of Nb and N co-doping on the electronic structure and band gap of SnO_2 semiconductor, further corroborating results of the experimental study.

Colossal Dielectric Behavior of Ga+Nb Co-Doped Rutile TiO2.

Science.gov (United States)

Dong, Wen; Hu, Wanbiao; Berlie, Adam; Lau, Kenny; Chen, Hua; Withers, Ray L; Liu, Yun

2015-11-18

Stimulated by the excellent colossal permittivity (CP) behavior achieved in In+Nb co-doped rutile TiO2, in this work we investigate the CP behavior of Ga and Nb co-doped rutile TiO2, i.e., (Ga(0.5)Nb(0.5))(x)Ti(1-x)O2, where Ga(3+) is from the same group as In(3+) but with a much smaller ionic radius. Colossal permittivity of up to 10(4)-10(5) with an acceptably low dielectric loss (tan δ = 0.05-0.1) over broad frequency/temperature ranges is obtained at x = 0.5% after systematic synthesis optimizations. Systematic structural, defect, and dielectric characterizations suggest that multiple polarization mechanisms exist in this system: defect dipoles at low temperature (∼10-40 K), polaronlike electron hopping/transport at higher temperatures, and a surface barrier layer capacitor effect. Together these mechanisms contribute to the overall dielectric properties, especially apparent observed CP. We believe that this work provides comprehensive guidance for the design of new CP materials.

Synthesis, structural characterization and dielectric properties of Nb doped BaTiO3/SiO2 core–shell heterostructure

International Nuclear Information System (INIS)

Cernea, M.; Vasile, B.S.; Boni, A.; Iuga, A.

2014-01-01

Highlights: • Optimal parameters for preparation by sol–gel of core–shell (BT-Nb 0.005 )/SiO 2 are presented in this paper. • Single crystalline BT-Nb 0.005 /SiO 2 core–shell composite with ∼34 nm shell thick was prepared. • The core–shell ceramic exhibits good dielectric properties and ferroelectric characteristics. -- Abstract: Perovskite complex ceramic oxides, BaTiO 3 doped with 0.5 mol%Nb 2 O 5 and then nanocoated with SiO 2 (abbreviated as BT-Nb 0.005 /SiO 2 ) was successful prepared using conventional sol–gel processing. Phase composition, particle morphology, structure, and electric properties of BT-Nb 0.005 core and BT-Nb 0.005 /SiO 2 core–shell were examined and compared, using X-ray diffraction, transmission electron microscopy and, dielectric and ferroelectric measurements. Core–shell composite with well-defined perovskite tetragonal phase of BaTiO 3 was achieved. Furthermore, single crystalline BT-Nb 0.005 /SiO 2 core–nanoshell heterostructure with ∼34 nm shell thick was prepared, which is a novelty in ferroelectrics field. The ferroelectric quality of BT-Nb 0.005 has suffered an alteration when the (BT-Nb 0.005 )/SiO 2 core–shell heterostructure was realized. One-dimensional BT-Nb 0.005 /SiO 2 core–shell heterostructure exhibits an improvement of dielectric losses and a decrease of dielectric constant, compared to uncoated BT-Nb 0.005 . The (BT-Nb 0.005 )/SiO 2 core–shell material could be interesting for application in the composite capacitors

Multi-level resistive switching behaviors and retention characteristics in ZnO/Nb:SrTiO3 heterojunction

Science.gov (United States)

Ren, Yong; Li, Jiachen; Zhang, Weifeng; Jia, Caihong

2017-10-01

Epitaxial ZnO thin films were grown on SrTiO3:Nb (NSTO) substrates by rf magnetron sputtering method. The multi-level resistance states were observed by applying different amplitudes and/or polarities of voltage pulses, which is supposed to be related to the drift of oxygen vacancies. Furthermore, the decay of retention is also corresponding to the migration of oxygen vacancies. The retention and cycle stability implies that the ZnO/Nb:SrTiO3 heterojunctions are promising for high density memory application.

Defect engineering of SrTiO3 thin films for resistive switching applications

International Nuclear Information System (INIS)

Wicklein, Sebastian

2013-01-01

As a matter of fact, the importance of (transition) metal oxides for modern applications in the field of energy and information technology (IT) for e.g. novel energy storage systems and solid state electronic devices is increasing. Previous studies discovered the importance of defects in an oxide for their functionality and emphasized the impact of stoichiometry on the oxide performance. A new field of interest of the memory technology sector is the so-called resistive switching phenomena where a voltage stimulus causes a thin oxide (≤10 nm) to change its resistance state from a high resistance state to a low resistance state and back. So called resistive RAM (ReRAM or RRAM) are deemed to be the future replacement (2015) for contemporary FLASH memory technology due to its extremely low energy consumption, its very fast read/write time (ns) and its possible node size 3 was used as an oxide model material and was deposited by pulsed laser deposition (PLD) onto doped and undoped SrTiO 3 single crystals to investigate the formation of defects as a function of the process parameters. By combining structural and chemical thin film analysis with detailed PLD plume diagnostics and modeling of the laser plume dynamics, it was possible to elucidate the different physical mechanisms determining the stoichiometry of SrTiO 3 during PLD. Deviations between thin film and target stoichiometry are basically a result of two effects, namely, incongruent ablation and preferential scattering of lighter ablated species during their motion towards the substrate in the O 2 background gas. It is shown that the SrTiO 3 system reacts to a non-stoichiometry with the systematic incorporation of titanium and strontium vacancies which could be detected by positron annihilation lifetime spectroscopy. The role of extrinsic dopands such as Fe is shown to have more complicated effects on the SrTiO 3 system than portrayed by theoretical considerations. The effect of defects on the resistive

Physics of SrTiO3-based heterostructures and nanostructures: a review.

Science.gov (United States)

Pai, Yun-Yi; Tylan-Tyler, Anthony; Irvin, Patrick; Levy, Jeremy

2017-08-30

1 Overview 1 1.1 Introduction 1 1.1.1 Oxide growth techniques are rooted in search for high-Tc superconductors 2 1.1.2 First reports of interface conductivity 2 1.2 2D physics 2 1.3 Emergent properties of oxide heterostructures and nanostructures 3 1.4 Outline 3 2 Relevant properties of SrTiO3 3 2.1 Structural properties and transitions 3 2.2 Ferroelectricity, Paraelectricity and Quantum Paraelectricity 4 2.3 Electronic structure 5 2.4 Defects 6 2.4.1 Oxygen vacancies 6 2.4.2 Terraces 7 2.5 Superconductivity 7 3 SrTiO3-based heterostructures and nanostructures 8 3.1 Varieties of heterostructures 8 3.1.1 SrTiO3 only 9 3.1.2 LaAlO3/SrTiO3 9 3.1.3 Other heterostructures formed with SrTiO3 10 3.2 Thin-film growth 10 3.2.1 Substrates 10 3.2.2 SrTiO3 surface treatment 11 3.2.3 Pulsed Laser Deposition 11 3.2.4 Atomic Layer Deposition 13 3.2.5 Molecular Beam Epitaxy 14 3.2.6 Sputtering 15 3.3 Device Fabrication 15 3.3.1 "Conventional" photolithography - Thickness Modulation, hard masks, etc. 15 3.3.2 Ion beam irradiation 16 3.3.3 Conductive-AFM lithography 16 4 Properties and phase diagram of LaAlO3/SrTiO3 16 4.1 Insulating state 16 4.2 Conducting state 17 4.2.1 Confinement thickness (the depth profile of the 2DEG) 17 4.3 Metal-insulator transition and critical thickness 18 4.3.1 Polar catastrophe ( electronic reconstruction) 18 4.3.2 Oxygen Vacancies 19 4.3.3 Interdiffusion 20 4.3.4 Polar Interdiffusion + oxygen vacancies + antisite pairs 20 4.3.5 Role of surface adsorbates 21 4.3.6 Hidden FE like distortion - Strain induced instability 21 4.4 Structural properties and transitions 21 4.5 Electronic band structure 22 4.5.1 Theory 22 4.5.2 Experiment 23 4.5.3 Lifshitz transition 24 4.6 Defects, doping, and compensation 25 4.7 Magnetism 25 4.7.1 Experimental evidence 25 4.7.2 Two types of magnetism 27 4.7.3 Ferromagnetism 27 4.7.4 Metamagnetism 28 4.8 Superconductivity 28 4.9 Optical properties 29 4.9.1 Photoluminesce

Optical properties of SrTiO3 films

International Nuclear Information System (INIS)

Agasiyev, A.A.; Magerramov, E.M.; Mammadov, M.Z.; Sarmasov, S.M.

2010-01-01

The spectrums of optical absorption of amorphous and single crystalline films SrTiO 3 at temperatures : 105 K, 300 K, 400 K are investigated. The temperature dependences of slope absorption edge, forbidden gap and characteristic constant of Urbah rule are obtained. The forbidden gap of single crystalline film SrTiO 3 and average shift shift of absorption edge degree are defined. It is established that edge of optical absorption of SrTiO 3 film is obeyed to Urbah rule and the absorption in the investigated region is caused by the transition of electron interacting with phonon

Sintering, microstructure and electrical conductivity of gadolinia-doped ceria with SrO, TiO2 and SrTiO3

International Nuclear Information System (INIS)

Dias, Maria Cely Freitas

2013-01-01

Ceria containing trivalent rare-earths is a solid electrolyte with higher ionic conductivity than the standard yttria fully-stabilized zirconia ionic conductor. This property turns these ceria-based ionic conductors promising materials for application in solid oxide fuel cells operating at intermediate temperatures (500-700 deg C). One of the most utilized approaches to optimize the electrical conductivity and other properties of these materials is the introduction of a second additive. In this work, ceria-20 mol% gadolinia with additions of 1, 2.5 and 5 mol% of SrO, TiO 2 and SrTiO 3 as co-additives were prepared by solid state reaction. The main purpose was to investigate the effects of the co-additives on densification, microstructure and electrical conductivity of the solid electrolyte. Sintered pellets were characterized by apparent density, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and electrical conductivity by impedance spectroscopy. The additives were found to exert different influences in all studied properties. The way they influence the solid electrolyte properties depends on the type and content of the additive. SrO addition to doped ceria improves the intergranular conductivity, but decreases the apparent density of the pellets. Increase of densification was obtained with TiO 2 addition. This additive promotes increase of the blocking of charge carriers at the grain boundaries due to solute exsolution and formation of the pyrochlore Gd 2 Ti 2 O 7 phase at grain boundaries for contents in excess of the solubility limit. No influence on densification was found for SrTiO 3 additions. (author)

Dielectric enhancement of BaTiO3/SrTiO3 superlattices with embedded Ni nanocrystals

International Nuclear Information System (INIS)

Xiong Zhengwei; Sun Weiguo; Wang Xuemin; Jiang Fan; Wu Weidong

2012-01-01

Highlights: ► The BaTiO 3 /SrTiO 3 superlattices with embedded Ni NCs were successfully fabricated by L-MBE. ► The influence with the various concentrations of Ni nanocrystals embedded in BaTiO 3 /SrTiO 3 superlattices was also discussed. ► The BaTiO 3 /SrTiO 3 superlattices with lower concentration of embedded Ni NCs had higher permittivity and dielectric loss compared with the pure BaTiO 3 /SrTiO 3 superlattices. ► The dielectric enhancement of BaTiO 3 /SrTiO 3 superlattices with embedded Ni NCs was proposed to explained by Drude quasi-free-electron theory. - Abstract: The self-organized Ni nanocrystals (NCs) were embedded in BaTiO 3 /SrTiO 3 superlattices using laser molecular beam epitaxy (L-MBE). The stress of the composite films was increased with the increasing concentration of embedded Ni NCs, as investigation in stress calculation. The influence with the various concentrations of Ni NCs embedded in BaTiO 3 /SrTiO 3 superlattices was also discussed. The internal stress of the films was too strong to epitaxial growth of BaTiO 3 /SrTiO 3 superlattices. Compared with the pure BaTiO 3 /SrTiO 3 superlattices, the BaTiO 3 /SrTiO 3 superlattices with lower concentration of embedded Ni NCs had higher permittivity and dielectric loss. Furthermore, the dielectric enhancement of BaTiO 3 /SrTiO 3 superlattices with embedded Ni NCs was proposed to explained by Drude quasi-free-electron theory.

Nb-doped rutile TiO₂: a potential anode material for Na-ion battery.

Science.gov (United States)

Usui, Hiroyuki; Yoshioka, Sho; Wasada, Kuniaki; Shimizu, Masahiro; Sakaguchi, Hiroki

2015-04-01

The electrochemical properties of the rutile-type TiO2 and Nb-doped TiO2 were investigated for the first time as Na-ion battery anodes. Ti(1-x)Nb(x)O2 thick-film electrodes without a binder and a conductive additive were prepared using a sol-gel method followed by a gas-deposition method. The TiO2 electrode showed reversible reactions of Na insertion/extraction accompanied by expansion/contraction of the TiO2 lattice. Among the Ti(1-x)Nb(x)O2 electrodes with x = 0-0.18, the Ti(0.94)Nb(0.06)O2 electrode exhibited the best cycling performance, with a reversible capacity of 160 mA h g(-1) at the 50th cycle. As the Li-ion battery anode, this electrode also attained an excellent rate capability, with a capacity of 120 mA h g(-1) even at the high current density of 16.75 A g(-1) (50C). The improvements in the performances are attributed to a 3 orders of magnitude higher electronic conductivity of Ti(0.94)Nb(0.06)O2 compared to that of TiO2. This offers the possibility of Nb-doped rutile TiO2 as a Na-ion battery anode as well as a Li-ion battery anode.

The role of the Mg2+ ions in Cr3+ spectroscopy for near-stoichiometric LiNbO3 crystals

International Nuclear Information System (INIS)

Han, T P J; Jaque, F; Bermudez, V; Dieguez, E

2003-01-01

The optical spectroscopy of Cr 3+ ions doped into near-stoichiometric LiNbO 3 crystals, pure and co-doped with MgO, has been investigated. In the near-stoichiometric LiNbO 3 :Cr(0.2 mol%):Mg(2 mol%) crystal, the optical spectra resemble those previously observed for congruent LiNbO 3 :Cr:MgO samples when the total MgO content exceeds the 4.6 mol% threshold. The coexistence of two types of Cr 3+ centre ([Cr] Li and [Cr] Nb ) characterized the optical and luminescence spectra of this sample. The concentration equilibrium between the two types of centre is strongly displaced towards the [Cr 3+ ] Nb centre, permitting us to obtain with accuracy the parameters of the broad bands. The R-line associated with the [Cr] Nb centre is only observable in the low-temperature emission spectrum. The Fano anti-resonance lines present have been observed to be more pronounced for the near-stoichiometric samples than for congruent ones

Intensive up-conversion photoluminescence of Er3+-doped Bi7Ti4NbO21 ferroelectric ceramics and its temperature sensing

Directory of Open Access Journals (Sweden)

Hua Zou

2014-10-01

Full Text Available The intensive up-conversion (UC photoluminescence and temperature sensing behavior of Er3+-doped Bi7Ti4NbO21(BTN ferroelectric ceramics prepared by a conventional solid-state reaction technique have been investigated. The X-ray diffraction and field emission scanning electron microscope analyses demonstrated that the Er3+-doped BTN ceramics are single phase and uniform flake-like structure. With the Er3+ ions doping, the intensive UC emission was observed without obviously changing the properties of ferroelectric. The optimal emission intensity was obtained when Er doping level was 15 mol.%. The temperature sensing behavior was studied by fluorescence intensity ratio (FIR technique of two green UC emission bands, and the experimental data fitted very well with the function of temperature in a range of 133–573 K. It suggested that the Er3+-doped BTN ferroelectric ceramics are very good candidates for applications such as optical thermometry, electro-optical devices and bio-imaging ceramics.

High Ic, YBa2Cu3O7-x films grown at very high rates by liquid assisted growth incorporating lightly Au-doped SrTiO3 buffers

International Nuclear Information System (INIS)

Kursumovic, A; Durrell, J H; Harrington, S; Wimbush, S; MacManus-Driscoll, J L; Maiorov, B; Zhou, H; Stan, L; Holesinger, T G; Wang, H

2009-01-01

YBa 2 Cu 3 O 7-x (YBCO) thick films were grown by hybrid liquid phase epitaxy (HLPE) on (001) SrTiO 3 (STO) substrates. In the presence of a 100 nm thick, 5 mol% Au-doped STO buffer, self-field critical current densities, J c sf , at 77 K of ∼2.4 MA cm -2 and critical currents, I c sf , up to 700 A (cm-width) -1 were achieved. The J c value is virtually independent of thickness and the growth rates are very high (∼1 μm min -1 ). From transmission electron microscopy (TEM), Y 2 O 3 nanocloud extended defects (∼100 nm in size) were identified as the pinning defects in the films. Enhanced random pinning was induced by the presence of Au in the buffer.

Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC

DEFF Research Database (Denmark)

Ou, Yiyu; Jokubavicius, Valdas; Kamiyama, Satoshi

2011-01-01

In the present work, we investigated donor-acceptor-pair emission in N-B doped fluorescent 6H-SiC, by means of photoluminescence, Raman spectroscopy, and angle-resolved photoluminescence. The photoluminescence results were interpreted by using a band diagram with Fermi-Dirac statistics. It is shown...... intensity in a large emission angle range was achieved from angle-resolved photoluminescence. The results indicate N-B doped fluorescent SiC as a good wavelength converter in white LEDs applications....

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.

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.

Imaging and tuning polarity at SrTiO3 domain walls

Science.gov (United States)

Frenkel, Yiftach; Haham, Noam; Shperber, Yishai; Bell, Christopher; Xie, Yanwu; Chen, Zhuoyu; Hikita, Yasuyuki; Hwang, Harold Y.; Salje, Ekhard K. H.; Kalisky, Beena

2017-12-01

Electrostatic fields tune the ground state of interfaces between complex oxide materials. Electronic properties, such as conductivity and superconductivity, can be tuned and then used to create and control circuit elements and gate-defined devices. Here we show that naturally occurring twin boundaries, with properties that are different from their surrounding bulk, can tune the LaAlO3/SrTiO3 interface 2DEG at the nanoscale. In particular, SrTiO3 domain boundaries have the unusual distinction of remaining highly mobile down to low temperatures, and were recently suggested to be polar. Here we apply localized pressure to an individual SrTiO3 twin boundary and detect a change in LaAlO3/SrTiO3 interface current distribution. Our data directly confirm the existence of polarity at the twin boundaries, and demonstrate that they can serve as effective tunable gates. As the location of SrTiO3 domain walls can be controlled using external field stimuli, our findings suggest a novel approach to manipulate SrTiO3-based devices on the nanoscale.

Structural and electronic properties of Mg and Mg-Nb co-doped TiO2 (101) anatase surface

International Nuclear Information System (INIS)

Sasani, Alireza; Baktash, Ardeshir; Mirabbaszadeh, Kavoos; Khoshnevisan, Bahram

2016-01-01

Highlights: • Formation energy of Mg and Mg-Nb co-doped TiO_2 anatase surface (101) is studied. • Effect of Mg defect to the TiO_2 anatase (101) surface and bond length distribution of the surface is studied and it is shown that Mg defects tend to stay far from each other. • Effect of Mg and Nb to the bond length distribution of the surface studied and it is shown that these defects tend to stay close to each other. • Effects of Mg and Mg-Nb defects on DSSCs using TiO_2 anatase hosting these defects are studied. - Abstract: In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO_2 anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO_2 surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase J_S_C of the surface while slightly decreasing V_O_C compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

Structures and electrical properties of Mn- and Co-doped lead-free ferroelectric K0.5Na0.5NbO3 films prepared by a chemical solution deposition method

International Nuclear Information System (INIS)

Wang, Lingyan; Ren, Wei; Goh, Phoi Chin; Yao, Kui; Shi, Peng; Wu, Xiaoqing; Yao, Xi

2013-01-01

The un-doped, 2 mol% Mn- and 2 mol% Co-doped K 0.5 Na 0.5 NbO 3 (KNN) films were prepared by a chemical solution deposition method. The crystalline phase and surface morphologies of KNN films hardly changed after Mn- and Co-doping. X-ray photoelectron spectrocopy analysis indicates that the introduction of both Mn and Co promoted the formation of KNN perovskite structure, and the most Mn 2+ and Co 2+ ions were oxidized into high-valence ions during thermal process. As a result, the leakage current density of the KNN films was decreased and the electrical properties were enhanced after the doping. - Highlights: • The leakage current density of K 0.5 Na 0.5 NbO 3 (KNN) films decreased after doping • The introduction of dopant promoted the formation of KNN perovskite structure • A portion of introduced doping ions became high-valent after heat-treatment

Orthorhombic strontium titanate in BaTiO sub 3 -SrTiO sub 3 superlattices

CERN Document Server

Rios, S; Jiang, A Q; Scott, J F; Lü, H; Chen, Z

2003-01-01

It has been suggested by several authors that SrTiO sub 3 layers in SrTiO sub 3 -BaTiO sub 3 superlattices should be tetragonal and ferroelectric at ambient temperatures, like the BaTiO sub 3 layers, rather than cubic, as in bulk SrTiO sub 3 , and that free-energy minimization requires continuity of the polarization direction. A recent ab initio calculation constrained solutions to this structure. Surprisingly, our x-ray study shows that the SrTiO sub 3 layers are orthorhombic with 0.03% in-plane strain, with the BaTiO sub 3 c-axis matching the SrTiO sub 3 a- and b-axis better than the c-axis; strain energy overcomes the cost in electrostatic energy. (letter to the editor)

Nb-doped TiO2 cathode catalysts for oxygen reduction reaction of polymer electrolyte fuel cells

KAUST Repository

Arashi, Takuya

2014-09-01

Nb-doped TiO2 particles were studied as electrocatalysts for the oxygen reduction reaction (ORR) under acidic conditions. The Nb-doped TiN nanoparticles were first synthesized by meso-porous C3N4 and then fully oxidized to Nb-doped TiO2 by immersing in 0.1 M H 2SO4 at 353 K for 24 h. Although the ORR activity of the as-obtained sample was low, a H2 treatment at relatively high temperature (1173 K) dramatically improved the ORR performance. An onset potential as high as 0.82 VRHE was measured. No degradation of the catalysts was observed during the oxidation-reduction cycles under the ORR condition for over 127 h. H2 treatment at temperatures above 1173 K caused the formation of a Ti4O7 phase, resulting in a decrease in ORR current. Elemental analysis indicated that the Nb-doped TiO 2 contained 25 wt% residual carbon. Calcination in air at 673 or 973 K eliminated the residual carbon in the catalyst, which was accompanied by a dramatic decrease in ORR activity. This post-calcination process may reduce the conductivity of the sample by filling the oxygen vacancies, and the carbon residue in the particle aggregates may enhance the electrocatalytic activity for ORR. The feasibility of using conductive oxide materials as electrocatalysts is discussed. © 2013 Elsevier B.V.

Nb-doped TiO2 cathode catalysts for oxygen reduction reaction of polymer electrolyte fuel cells

KAUST Repository

Arashi, Takuya; Seo, Jeongsuk; Takanabe, Kazuhiro; Kubota, Jun; Domen, Kazunari

2014-01-01

Nb-doped TiO2 particles were studied as electrocatalysts for the oxygen reduction reaction (ORR) under acidic conditions. The Nb-doped TiN nanoparticles were first synthesized by meso-porous C3N4 and then fully oxidized to Nb-doped TiO2 by immersing in 0.1 M H 2SO4 at 353 K for 24 h. Although the ORR activity of the as-obtained sample was low, a H2 treatment at relatively high temperature (1173 K) dramatically improved the ORR performance. An onset potential as high as 0.82 VRHE was measured. No degradation of the catalysts was observed during the oxidation-reduction cycles under the ORR condition for over 127 h. H2 treatment at temperatures above 1173 K caused the formation of a Ti4O7 phase, resulting in a decrease in ORR current. Elemental analysis indicated that the Nb-doped TiO 2 contained 25 wt% residual carbon. Calcination in air at 673 or 973 K eliminated the residual carbon in the catalyst, which was accompanied by a dramatic decrease in ORR activity. This post-calcination process may reduce the conductivity of the sample by filling the oxygen vacancies, and the carbon residue in the particle aggregates may enhance the electrocatalytic activity for ORR. The feasibility of using conductive oxide materials as electrocatalysts is discussed. © 2013 Elsevier B.V.

Effects of film thickness and preferred orientation on the dielectric properties of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 films

International Nuclear Information System (INIS)

Cao, L Z; Fu, W Y; Wang, S F; Wang, Q; Sun, Z H; Yang, H; Cheng, B L; Wang, H; Zhou, Y L

2007-01-01

(Bi 1.5 Zn 0.5 )(Zn 0.5 Nb 1.5 )O 7 (BZN) films with different thicknesses and preferred orientations have been fabricated on Nb doped SrTiO 3 substrates by pulsed laser deposition. As the thickness increases, the permittivity increases, and the dielectric loss decreases, while the tunability only has a little variation. The asymmetric behaviour of the electric field dependent permittivity reduces gradually with the increasing thickness, which should be attributed to the decrease in the effect of the interfacial layer between the dielectric film and substrate (electrode). Furthermore, compared with the (1 0 0) oriented BZN film, BZN film with (1 1 1) preferred orientation exhibits high dielectric loss

Structural and electronic properties of Mg and Mg-Nb co-doped TiO2 (101) anatase surface

Energy Technology Data Exchange (ETDEWEB)

Sasani, Alireza [Department of Science, Karaj Islamic Azad University, Karaj, Alborz, P.O. Box 31485-313 (Iran, Islamic Republic of); Baktash, Ardeshir [Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167 (Iran, Islamic Republic of); Mirabbaszadeh, Kavoos, E-mail: mirabbas@aut.ac.ir [Department of Energy Engineering and Physics, Amirkabir University of Technology, Tehran, P. O. Box 15875-4413 (Iran, Islamic Republic of); Khoshnevisan, Bahram [Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167 (Iran, Islamic Republic of)

2016-10-30

Highlights: • Formation energy of Mg and Mg-Nb co-doped TiO{sub 2} anatase surface (101) is studied. • Effect of Mg defect to the TiO{sub 2} anatase (101) surface and bond length distribution of the surface is studied and it is shown that Mg defects tend to stay far from each other. • Effect of Mg and Nb to the bond length distribution of the surface studied and it is shown that these defects tend to stay close to each other. • Effects of Mg and Mg-Nb defects on DSSCs using TiO{sub 2} anatase hosting these defects are studied. - Abstract: In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO{sub 2} anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO{sub 2} surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase J{sub SC} of the surface while slightly decreasing V{sub OC} compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

Effect of Dopant Loading on the Structural and Catalytic Properties of Mn-Doped SrTiO3 Catalysts for Catalytic Soot Combustion

Directory of Open Access Journals (Sweden)

Santiago Iván Suárez-Vázquez

2018-02-01

Full Text Available Soot particles have been associated with respiratory diseases and cancer. To decrease these emissions, perovskite-mixed oxides have been proposed due to their thermal stability and redox surface properties. In this work, SrTiO3 doped with different amounts of Mn were synthesized by the hydrothermal method and tested for soot combustion. Results show that at low Mn content, structural distortion, and higher Oads/Olat ratio were observed which was attributed to the high content of Mn3+ in Ti sites. On the other hand, increasing the Mn content led to surface segregation of manganese oxide. All synthesized catalysts showed mesopores in the range of 32–47 nm. In the catalytic combustion of soot, the samples synthesized in this work lowered the combustion temperature by more than 100 °C compared with the uncatalyzed reaction. The sample doped with 1 wt % of Mn showed the best catalytic activity. The activation energy of these samples was also calculated, and the order of decreasing activation energy is as follows: uncatalyzed > Mn0 > Mn8 > Mn4 > Mn1. The best catalytic activity for Mn1 was attributed to its physicochemical properties and the mobility of the oxygen from the bulk to the surface at temperatures higher than 500 °C.

Dielectric properties of Li doped Li-Nb-O thin films

Energy Technology Data Exchange (ETDEWEB)

Perentzis, G.; Horopanitis, E.E.; Papadimitriou, L. [Aristotle University of Thessaloniki, Department of Physics, 54124 Thessaloniki (Greece); Durman, V.; Saly, V.; Packa, J. [Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovicova 3, 81219 Bratislava (Slovakia)

2007-03-15

Lithium niobate LiNbO{sub 3} was prepared as a thin film layered structure deposited on stainless steel substrate using e-gun evaporation. The Li doping was provided for by the formation of Li-Nb-O/Li/LiNb-O sandwich structure and annealing at about 250 C. AC impedance spectroscopy measurements were performed on the samples at temperatures from the interval between 28 and 165 C and in a frequency range of 10{sup -3} to 10{sup 6} Hz. Using the values Z' and Z'' at different frequencies, the dielectric parameters - parts of the complex permittivity {epsilon}' and {epsilon}'' and loss tangent tan {delta} were calculated. The results prove validity of the proposed equivalent circuit containing parallel RC elements connected in series where the first RC element represents the bulk of material and the second RC element belongs to the double layer at the metal interface. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

LiNbO3 :Pr3+ : A Multipiezo Material with Simultaneous Piezoelectricity and Sensitive Piezoluminescence.

Science.gov (United States)

Tu, Dong; Xu, Chao-Nan; Yoshida, Akihito; Fujihala, Masayoshi; Hirotsu, Jou; Zheng, Xu-Guang

2017-06-01

Red-emitting piezoluminescence (elasticoluminescence) is achieved by doping rare earth Pr 3+ into the well-known piezoelectric matrix, LiNbO 3 . By precisely tuning the Li/Nb ratio in nonstoichiometric Li x NbO 3 :Pr 3+ , a material that exhibits an unusually high piezoluminescence intensity, which far exceeds that of any well-known piezoelectric material, is produced. Li x NbO 3 :Pr 3+ shows excellent strain sensitivity at the lowest strain level, with no threshold for stress sensing. These multipiezo properties of sensitive piezoluminescence in a piezoelectric matrix are ideal for microstress sensing, damage diagnosis, electro-mechano-optical energy conversion, and multifunctional control in optoelectronics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dielectric, piezoelectric properties of MnO2-doped (K0.5Na0.5)NbO3–0.05LiNbO3 crystal grown by flux-Bridgman method

International Nuclear Information System (INIS)

Liu, Ying; Xu, Guisheng; Liu, Jinfeng; Yang, Danfeng; Chen, Xiaxia

2014-01-01

Highlights: • KNN–0.05LN based single crystals were grown by flux-Bridgman method. • Dielectric, piezoelecrc and ferroelectric properties were studied. • The effect of MnO 2 doping on the crystals' properties. • Dielectric and other properties were improved due to MnO 2 doping. - Abstract: Lead-free potassium sodium niobate piezoelectric single crystals substituted with lithium and then doped with MnO 2 (K 0.5 Na 0.5 )NbO 3 –0.05LiNbO 3 –yMnO 2 (y = 0%, 1.0% and 1.5%) (abbreviated as KNN–0.05LN–yMnO 2 ) have been grown by flux-Bridgman method using KCl–K 2 CO 3 eutectic composition as the flux. Their actual composition as well as the dielectric and piezoelectric properties were studied. Their actual composition deviated from the ratio of the raw materials due to different segregation coefficients of K and Na. The orthorhombic–tetragonal (T o–t ) and tetragonal–cubic phase transition temperature (the Curie temperature T c ) of the single crystal appears at 186 °C and 441 °C, respectively, for KNN–0.05LN–1.0%MnO 2 , shift to higher temperatures compared with that of pure KNN–0.05LN crystals, according to the dielectric permittivity versus temperature loops. The KNN–0.05LN–1.0%MnO 2 (001) plate shows higher piezoelectric coefficient d 33 and dielectric permittivity ε r when compared with pure KNN–0.05LN crystal, being on the order of 226 pC/N and 799 (161 pC/N and 530 for KNN–0.05LN), respectively. These excellent properties show that MnO 2 dopant is effective in improving KNN–0.05LN based piezoelectric crystals

Effects of Y{sub 2}O{sub 3}/CeO{sub 2} co-doping on microwave dielectric properties of Ba(Co{sub 0.6}Zn{sub 38}){sub 1/3}Nb{sub 2/3}O{sub 3} ceramics

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yuqin; Zhou, Xiaohua, E-mail: 1250590698@qq.com; Yang, Xinshi; Sun, Chengli; Yang, Fan; Chen, Hetuo

2016-09-15

The effects of CeO{sub 2}/Y{sub 2}O{sub 3} co-doping on the microstructure and microwave dielectric properties of Ba(Co{sub 0.6}Zn{sub 0.38}){sub 1/3}Nb{sub 2/3}O{sub 3}-xA-xB (x = 0,1,2,3,4,6; A = 0.1204 wt%Y{sub 2}O{sub 3}; B = 0.1 wt%CeO{sub 2}) ceramics prepared by the conventional solid-state route technique were investigated. The X-ray diffraction (XRD) results presented that all the well sintered samples exhibited the main phase BaZn{sub 0.33}Nb{sub 0.67}O{sub 3}−Ba{sub 3}CoNb{sub 2}O{sub 9}. A certain amount of Ba{sub 8}CoNb{sub 6}O{sub 24} surface secondary phase and minority phase of Ba{sub 5}Nb{sub 4}O{sub 15} were also observed in all sintered ceramics. The 1:2 B-site cation ordering degree was found to influenced by the substitution of Y{sup 3+} and Ce{sup 4+} in the crystal lattice, especially for x = 0.02. Then the scanning electron microscopy (SEM) picture of the optimally well-sintered (1350 °C for 20 h) ceramic has shown a dense microstructure. Although the ε{sub r} almost kept unchanged, appropriate doping content would greatly improve the Q × f value. Meanwhile, the τ{sub f} value first declined and then increased with increasing x. At last, the excellent microwave dielectric properties of ε{sub r} = 36.09, Q × f = 72006 GHz, τ{sub f} = 3.35 ppm/ºC were obtained for the ceramic with x = 0.02 sintered in air at 1350 °C for 20 h. - Graphical abstract: Fig. SEM images of as-sintered Ba(Co{sub 0.6}Zn{sub 0.38}){sub 1/3}Nb{sub 2/3}O{sub 3}-xA-Xb (A = 0.1204 wt%Y{sub 2}O{sub 3}; B = 0.1 wt%CeO{sub 2)}ceramics: (a) x = 0,(b) x = 0.01,(c) x = 0.02,(d) x = 0.03, (e) x = 0.04,(f) x = 0.06. The images confirmed the presences of two phases on the surface of the ceramics, plate-shaped grains (Ba{sub 8}(C{sub O},Zn){sub 1}Nb{sub 6}O{sub 24}phase) and needle-shaped grains (Ba{sub 3}(Co{sub 0.6}Zn{sub 0.38}){sub 1}Nb{sub 2}O{sub 9} phase). As a small content of CeO{sub 2}/Y{sub 2}O{sub 3} (x = 0.01–0.04) was codoped into the BCZN ceramics, the

Grain boundary defect compensation in Ti-doped BaFe{sub 0.5}Nb{sub 0.5}O{sub 3} ceramics

Energy Technology Data Exchange (ETDEWEB)

Sun, Xiaojun; Deng, Jianming; Liu, Saisai; Yan, Tianxiang; Fang, Liang; Liu, Laijun [Guilin University of Technology, Key Laboratory of Nonferrous Materials and New Processing Technology, Ministry of Education, College of Materials Science and Engineering, Guangxi Universities Key Laboratory of Non-ferrous Metal Oxide Electronic Functional Materials and Devices, Guilin (China); Peng, Biaolin [Guangxi University, School of Physical Science and Technology and Guangxi Key Laboratory for Relativistic Astrophysics, Nanning (China); Jia, Wenhao [Shanghai Getong Enterprise Co., Ltd., Shanghai (China); Mei, Zaoming [Henan LiHeng Building Materials Co., Ltd., Zhengzhou (China); Su, Hongbo [Henan Province Product Quality Supervision and Inspection Center, Zhengzhou (China)

2016-09-15

Giant dielectric ceramics Ba(Nb{sub 0.5}Fe{sub 0.5-x}Ti{sub x})O{sub 3} (BNFT) have been fabricated by a conventional solid-state reaction. According to X-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric with Pm-3m space group. The real part (ε') of dielectric permittivity and dielectric loss (tan δ) of the BNFT ceramics was measured in a frequency range from 40 Hz to 100 MHz at room temperature. The (ε') of all these samples displays a high value (∝6500) and a small frequency-dependence from 1 kHz to 1 MHz. We have established a link between conductivity activation energy and defect compensation at grain boundaries. The Ti{sup 4+}-doped Ba(Nb{sub 0.5}Fe{sub 0.5})O{sub 3} as a donor makes a great influence on the grain boundary behavior, which restricts the migration of oxygen vacancy and depresses dielectric loss factor for Ba(Nb{sub 0.5}Fe{sub 0.5})O{sub 3} ceramics. (orig.)

Effects of compositions and Nb-doping on microstructure and piezoelectric properties of PMS-PZ-PT system

Energy Technology Data Exchange (ETDEWEB)

Jiwen, Long; Haiyan, Chen; Zhongyan, Meng

2003-05-25

Sr-substituted (2 mol%) xPMS-(1-x)(PZ-PT) compositions were investigated systematically as a function of PMS concentrations as well as Niobium (Nb) contents. X-ray diffraction (XRD) patterns show that phases shift from tetragonal phase to rhombohedral phase with the increase of PMS concentrations and with the increase of Nb-doping contents in PMS2. The compositions with x=0.05 (PMS2) was found to have superior piezoelectric properties. The properties of the PMS2 compositions were optimized by the Nb-doping contents of 0.1 mol% (d{sub 33}=450 pC N{sup -1}, K{sub p}=0.65, Q{sub m}=1210). The compositions of PMS2 and 0.1 mol% Nb-doped compositions of PMS2 are practically suitable for ultrasonic motor (USM) applications.

Depinning of the ferroelectric domain wall in congruent LiNbO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Lee, Donghwa, E-mail: donghwa96@jnu.ac.kr [School of Materials Science and Engineering, Chonnam National University, Gwangju 61186 (Korea, Republic of); Gopalan, Venkatraman [Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Phillpot, Simon R. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)

2016-08-22

The high coercive field, E{sub c}, of congruent LiNbO{sub 3} can be reduced by doping with Mg or Zn atoms, or by increasing the temperature above a threshold value. The physical origin for this reduction is not currently understood. Here, density functional theory calculations illustrate the atomic origin of the change in the switching field of the congruent LiNbO{sub 3}. They show that the high E{sub c} in the congruent LiNbO{sub 3} is a result of niobium antisite atoms on the lithium sublattice, pinning the motion of the domain walls. Thus, the healing of antisites by diffusion can significantly reduce the coercive field. In addition, this work demonstrates that the migration of these niobium antisites can be enhanced by doping or by changing the temperature. Thus, the depinning process of the congruent LiNbO{sub 3} is understood by the migration of the niobium antisite defect across the domain wall.

Role of alkali carbonate and salt in topochemical synthesis of K1/2Na1/2NbO3 and NaNbO3 templates

Science.gov (United States)

Lee, Jae-Seok; Jeon, Jae-Ho; Choi, Si-Young

2013-11-01

Since the properties of lead-free piezoelectric materials have thus far failed to meet those of lead-based materials, either chemical doping or morphological texturing should be employed to improve the piezoelectric properties of lead-free piezoelectric ceramics. The goal of this study was to synthesize plate-like K1/2Na1/2NbO3 and NaNbO3 particles, which are the most favorable templates for morphological texturing of K1/2Na1/2NbO3 ceramics. To achieve this goal, Bi2.5Na3.5Nb5O18 precursors in a plate-like shape were first synthesized and subsequently converted into K1/2Na1/2NbO3 or NaNbO3 particles that retain the morphology of Bi2.5Na3.5Nb5O18. In this study, we found that sodium or potassium carbonate does not play a major role in converting the Bi2.5Na3.5Nb5O18 precursor to K1/2Na1/2NbO3 or NaNbO3, on the contrary to previous reports; however, the salt contributes to the conversion reaction. All synthesis processes have been performed via a molten salt method, and scanning electron microscopy, scanning probe microscopy, and inductively coupled plasma mass spectroscopy were used to characterize the synthesized K1/2Na1/2NbO3 or NaNbO3 templates.

An investigation of the Nb doping effect on structural, morphological, electrical and optical properties of spray deposited F doped SnO2 films

Science.gov (United States)

Turgut, G.; Keskenler, E. F.; Aydın, S.; Yılmaz, M.; Doǧan, S.; Düzgün, B.

2013-03-01

F and Nb + F co-doped SnO2 thin films were deposited on glass substrates by the spray pyrolysis method. The microstructural, morphological, electrical and optical properties of the 10 wt% F doped SnO2 (FTO) thin films were investigated specifically for niobium (Nb) doping in the range of 0-4 at.% with 1 at.% steps. As shown by the x-ray diffraction patterns, the films exhibited a tetragonal cassiterite structure with (200) preferential orientation. It was observed that grain sizes of the films for (200) and (301) peaks depended on the Nb doping concentration and varied in the range of 25.11-32.19 and 100.6-183.7 nm, respectively. The scanning electron microscope (SEM) micrographs showed that the FTO films were made of small pyramidal grains, while doubly doped films were made of small pyramidal grains and big polyhedron grains. From electrical studies, although 1 at.% Nb doped FTO films have the lowest sheet resistance and resistivity values, the highest figure-of-merit and optical band gap values obtained for FTO films were 16.2 × 10-2 Ω-1 and 4.21 eV, respectively. Also, infrared reflectivity values of the films were in the range of 97.39-98.98%. These results strongly suggest that these films are an attractive candidate for various optoelectronic applications and for photothermal conversion of solar energy.

Microscopic observation of ferroelectric domains in SrTiO3 using birefringence imaging techniques under high electric fields

International Nuclear Information System (INIS)

Manaka, Hirotaka; Nozaki, Hirofumi; Miura, Yoko

2017-01-01

Phase transitions in SrTiO 3 between quantum paraelectric, coherent paraelectric, and electric-field-induced ferroelectric states are governed by tetragonal domains with quantum fluctuations. However, their characteristics are still unclear. To observe the electric-field-induced ferroelectric state using birefringence imaging techniques, we developed a suitable sample holder to apply high electric fields of up to E ≃ 5 kV/cm and temperatures down to T = 20 K. From birefringence imaging measurements of the ferroelectric LiNbO 3 with varying electric field, distributions of the electric field in the sample stage were found to be negligible. In SrTiO 3 , a huge-retardance area corresponding to the ferroelectric domains appears at E > 2 kV/cm and T ≤ 60 K even though the paraelectric domains partially remain. Furthermore, the fast-axis direction rotates by 90° at the ferroelectric phase transition because of an electrostrictive effect in ferroelectrics. The phase diagram of the critical electric field and temperature agrees with previous reports obtained from dielectric and neutron scattering measurements. (author)

Surface energy effects on the stability of anatase and rutile nanocrystals: A predictive diagram for Nb_2O_5-doped-TiO_2

International Nuclear Information System (INIS)

Silva, Andre Luiz da; Hotza, Dachamir; Castro, Ricardo H.R.

2017-01-01

Highlights: • Anatase-rutile phase transition diagram was built for nano Nb_2O_5-doped-TiO_2. • Nb_2O_5-doping postpones the anatase-to-rutile transition. • The stability crossover for TiO_2 was 17.3 nm, for 2 mol% Nb_2O_5-doped-TiO_2 ∼30 nm. • The surface energy for Nb_2O_5-doped-TiO_2 decreases systematically with Nb concentration. - Abstract: Titanium dioxide nanoparticles are widely used for photocatalysis, and the relative fraction of titanium dioxide polymorph, i.e. anatase, rutile, or brookite, significantly affects the final performance. Even though conventional phase diagrams indicate a higher stability for the rutile polymorph, it is well established that nanosizes benefit the anatase phase due to its smaller surface energy. However, doping elements are expected to change this behavior, once changes in both surface and bulk energies may occur. Nb_2O_5 is commonly added to TiO_2 to allow property control. However, the effect of niobium on the relative stability of anatase and rutile phases is not well understood from the thermodynamic point of view. The objective of this work was to build a new predictive nanoscale phase diagram for Nb_2O_5-doped TiO_2. Water adsorption microcalorimetry and high temperature oxide melt solution were used to obtain the surface and bulk enthalpies. The phase diagram obtained shows the stable titania polymorph as a function of the composition and size.

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.

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.

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.

Effect of Sr-doping of LaMnO3 spacer on modulation-doped two-dimensional electron gases at oxide interfaces

DEFF Research Database (Denmark)

Chen, Yunzhong; Gan, Yulin; Christensen, Dennis Valbjørn

2017-01-01

Modulation-doped oxide two-dimensional electron gas formed at the LaMnO3 (LMO) buffered disorderd-LaAlO3/SrTiO3 (d-LAO/LMO/STO) heterointerface provides new opportunities for electronics as well as quantum physics. Herein, we studied the dependence of Sr-doping of La1-xSrxMnO3 (LSMO, x = 0, 1/8, ...... of LSMO during the deposition of disordered LAO or that the energy levels of Mn 3d electrons at the interface of LSMO/STO are hardly varied even when changing the LSMO composition from LMO to SrMnO3....

Investigation of Upconversion, downshifting and quantum –cutting behavior of Eu3+, Yb3+, Bi3+ co-doped LaNbO4 phosphor as a spectral conversion material

Science.gov (United States)

Dwivedi, A.; Mishra, K.; Rai, S. B.

2018-06-01

This work presents the spectral conversion characteristics [upconversion (UC), downshifting (DS) and quantum–cutting (QC) optical processes] of Eu3+, Yb3+ and Bi3+ co-doped LaNbO4 (LBO) phosphor samples synthesized by solid state reaction technique. The crystal structure and the pure phase formation have been confirmed by x-ray diffraction (XRD) measurements. The surface morphology and particle size are studied by scanning electron microscopy (SEM). The rarely observed intense red UC emission from Eu3+ ion has been successfully obtained in Eu3+/Yb3+ co-doped LaNbO4 phosphor (on excitation with 980 nm) by optimizing the concentrations of Eu3+ and Yb3+ ions. The downshifting (DS) behavior has been studied by photoluminescence (PL) measurements on excitation with 265 nm wavelength from a Xe lamp source. A broad blue emission in the region 300–550 nm with its maximum ∼415 nm due to charge transfer band (CTB) of the host and large number of sharp peaks due to f-f transitions of Eu3+ ion have been observed. The energy transfer has been observed from (NbO4)3‑ to Eu3+ ion and the fluorescence emission has been optimized by varying the concentration of Eu3+ ion. An intense red emission has also been observed corresponding to 5D0 → 7F2 transition of Eu3+ ion at 611 nm in LBO: 0.09Eu3+ phosphor on excitation with 394 nm. The luminescence properties of Eu3+ ion are enhanced further through the sensitization effect of Bi3+ ion. The near infra-red (NIR) quantum cutting (QC) behavior due to Yb3+ ion has been monitored on excitation with 265 as well as 394 nm. The NIR QC is observed due to 2F5/2 → 2F7/2 transition of Yb3+ ion via co-operative energy transfer (CET) process from (NbO4)3‑ as well as Eu3+ ions to Yb3+ ion. This multimodal behavior (UC, DS and QC) makes this a promising phosphor material for multi-purpose spectral converter.

Determination of the electrostatic potential distribution in Pt/Fe:SrTiO3/Nb:SrTiO3 thin-film structures by electron holography

Science.gov (United States)

Marchewka, Astrid; Cooper, David; Lenser, Christian; Menzel, Stephan; Du, Hongchu; Dittmann, Regina; Dunin-Borkowski, Rafal E.; Waser, Rainer

2014-11-01

We determined the electrostatic potential distribution in pristine Pt/Fe:SrTiO3/Nb:SrTiO3 structures by electron holography experiments, revealing the existence of a depletion layer extending into the Nb-doped bottom electrode. Simulations of potential profiles in metal-insulator-metal structures were conducted assuming different types and distributions of dopants. It is found that the presence of acceptor-type dopant concentrations at the Fe:SrTiO3/Nb:SrTiO3 interface with a donor-doped insulating layer provides a good match to the measured profile. Such acceptor-type interface concentrations may be associated with Sr vacancies on the Nb:SrTiO3 side of the bottom interface.

Spectral and laser properties of Er3+/Yb3+/Ce3+ tri-doped Ca3NbGa3Si2O14 crystal at 1.55 µm

Science.gov (United States)

Gong, Guoliang; Chen, Yujin; Lin, Yanfu; Huang, Jianhua; Gong, Xinghong; Luo, Zundu; Huang, Yidong

2018-04-01

An Er3+/Yb3+/Ce3+ tri-doped Ca3NbGa3Si2O14 (CNGS) crystal was grown by the Czochralski method. Spectral properties of the crystal, including the polarized absorption and fluorescence spectra, the fluorescence decay, as well as the energy transfer efficiency from Yb3+ to Er3+ were investigated in detail. End-pumped by a 976 nm diode laser, a 1556 nm continuous-wave laser with a maximum output power of 202 mW and a slope efficiency of 11.4% was achieved in the Er,Yb,Ce:CNGS crystal. The results indicate the Er,Yb,Ce:CNGS crystal is a promising 1.55 µm laser gain medium.

Enhanced photovoltaic currents in strained Fe-doped LiNbO{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Inoue, Ryotaro [Division of Physics, Institute of Liberal Education, School of Medicine, Nihon University, 31-10, Ooyaguchi-kamicho, Itabashi-ku, Tokyo 173-8601 (Japan); Takahashi, Shusuke; Kitanaka, Yuuki; Oguchi, Takeshi; Noguchi, Yuji; Miyayama, Masaru [Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8654 (Japan)

2015-12-15

We investigate the impact of strain on photovoltaic current (J{sub z}) characteristics for iron-doped LiNbO{sub 3} (Fe-LN) under visible light illumination by thin-film experiments. The J{sub z} values are demonstrated to be dramatically enhanced for the film with a tensile strain along the P{sub s} direction, which is over 500 times as large as that of the bulk (strain-free) Fe-LN crystals. Density functional theory (DFT) calculations show that the tensile strain increases an off-center displacement of Fe{sup 2+} that is opposite to the P{sub s} direction. Our experimental and DFT study demonstrates that the control of the lattice strain is effective in enhancing the photovoltaic effect in the Fe-LN system. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Strontium Titanate-based Composite Anodes for Solid Oxide Fuel Cells

DEFF Research Database (Denmark)

Blennow Tullmar, Peter; Kammer Hansen, Kent; Wallenberg, L.R.

2008-01-01

Surfactant-assisted infiltration of Gd-doped ceria (CGO) in Nb-doped SrTiO3 (STN) was investigated as a potential fuel electrode for solid oxide fuel cells (SOFC). An electronically conductive backbone structure of STN was first fabricated at high temperatures and then combined with the mixed con...

First-principles calculation of the effects of Li-doping on the structure and piezoelectricity of (K0.5Na0.5)NbO3 lead-free ceramics.

Science.gov (United States)

Yang, D; Wei, L L; Chao, X L; Yang, Z P; Zhou, X Y

2016-03-21

The crystal structures of the lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 and (K0.5Na0.5)0.94Li0.06NbO3 prepared by a solid-state method were investigated using first-principles calculations. The calculated values of piezoelectricity were in good agreement with the experimental data. We found that the primary contribution to piezoelectricity in this material comes from the hybridization of the O 2p and Nb 4d orbitals, which causes a change in the Nb-O bond length and the distortion of the Nb-O octahedral structure. Analysis of the band structure and the total density of states revealed that Li-doped (K0.5Na0.5)NbO3 enhances hybridization of the O 2p and Nb 4d orbitals. This hybridization enhancement further reduces the Nb-O1 bond length and enhances the distortion of the Nb-O octahedron along the [001] direction, which may be the main reason for the improvement of the piezoelectric properties. In addition, the piezoelectric coefficients are calculated here, which show the same trend as the experimental results.

Nb and Ta Co-Doped TiO2 Transparent Conductive Thin Films by Magnetron Sputtering: Fabrication, Structure, and Characteristics

Science.gov (United States)

Liu, Yang; Peng, Qian; Qiao, Yadong; Yang, Guang

2018-06-01

Nb and Ta co-doped anatase titanium dioxide (NTTO) nanocrystalline thin films were deposited on quartz and Si (100) substrates by RF magnetron sputtering. The influence of RF power on the growth, structure, morphology, and properties of the samples are discussed in detail. X-ray diffraction measurements show that the films are polycrystalline with anatase tetragonal structure, which is further confirmed by Raman spectroscopy analysis. Meanwhile, Raman spectroscopy results indicate that the peak width of E g(1) mode, which is directly correlated to the carrier density, changes obviously with RF power. It is found that the substitution of Nb5+ and Ta5+ at Ti site is significantly improved with the increase of RF power from 150 W to 210 W. For the sample deposited at 210 W, the optical transmittance is above 82% in the visible range and the electrical resistivity is as low as 1.3 × 10-3 Ω cm with carrier density of 1.1 × 1021 cm-3 and Hall mobility of 4.5 cm2 V-1 s-1. The optical and electrical properties of NTTO thin films can be compared to those of Nb or Ta doped anatase TiO2. However, co-doping with Nb and Ta gives a possible platform to complement the limitations of each individual dopant.

Piezoelectric properties and temperature stability of Mn-doped Pb(Mg1/3Nb2/3)-PbZrO3-PbTiO3 textured ceramics

Science.gov (United States)

Yan, Yongke; Cho, Kyung-Hoon; Priya, Shashank

2012-03-01

In this letter, we report the electromechanical properties of textured 0.4Pb(Mg1/3Nb2/3)O3-0.25PbZrO3-0.35PbTiO3 (PMN-PZT) composition which has relatively high rhombohedral to tetragonal (R-T) transition temperature (TR-T of 160 °C) and Curie temperature (TC of 234 °C) and explore the effect of Mn-doping on this composition. It was found that MnO2-doped textured PMN-PZT ceramics with 5 vol. % BaTiO3 template (T-5BT) exhibited inferior temperature stability. The coupling factor (k31) of T-5BT ceramic started to degrade from 75 °C while the random counterpart showed a very stable tendency up to 180 °C. This degradation was associated with the "interface region" formed in the vicinity of BT template. MnO2 doped PMN-PZT ceramics textured with 3 vol. % BT and subsequently poled at 140 °C (T-3BT140) exhibited very stable and high k31 (>0.53) in a wide temperature range from room temperature to 130 °C through reduction in the interface region volume. Further, the T-3BT140 ceramic exhibited excellent hard and soft combinatory piezoelectric properties of d33 = 720 pC/N, k31 = 0.53, Qm = 403, tan δ = 0.3% which are very promising for high power and magnetoelectric applications.

Metastable honeycomb SrTiO_3/SrIrO_3 heterostructures

International Nuclear Information System (INIS)

Anderson, T. J.; Ryu, S.; Podkaminer, J. P.; Ma, Y.; Eom, C. B.; Zhou, H.; Xie, L.; Irwin, J.; Rzchowski, M. S.; Pan, X. Q.

2016-01-01

Recent theory predictions of exotic band topologies in (111) honeycomb perovskite SrIrO_3 layers sandwiched between SrTiO_3 have garnered much attention in the condensed matter physics and materials communities. However, perovskite SrIrO_3 film growth in the (111) direction remains unreported, as efforts to synthesize pure SrIrO_3 on (111) perovskite substrates have yielded films with monoclinic symmetry rather than the perovskite structure required by theory predictions. In this study, we report the synthesis of ultra-thin metastable perovskite SrIrO_3 films capped with SrTiO_3 grown on (111) SrTiO_3 substrates by pulsed laser deposition. The atomic structure of the ultra-thin films was examined with scanning transmission electron microscopy (STEM), which suggests a perovskite layering distinct from the bulk SrIrO_3 monoclinic phase. In-plane 3-fold symmetry for the entire heterostructure was confirmed using synchrotron surface X-ray diffraction to measure symmetry equivalent crystal truncation rods. Our findings demonstrate the ability to stabilize (111) honeycomb perovskite SrIrO_3, which provides an experimental avenue to probe the phenomena predicted for this material system.

Enhanced photovoltaic performance of a quantum dot-sensitized solar cell using a Nb-doped TiO2 electrode

International Nuclear Information System (INIS)

Jiang, Lei; You, Ting; Deng, Wei-Qiao

2013-01-01

In this work Nb-doped anatase TiO 2 nanocrystals are used as the photoanode of quantum-dot-sensitized solar cells. A solar cell with CdS/CdSe quantum dots co-sensitized 2.5 mol% Nb-doped anatase TiO 2 nanocrystals can achieve a photovoltaic conversion efficiency of 3.3%, which is almost twice as high as the 1.7% obtained by a cell based on undoped TiO 2 nanocrystals. The incident photon-to-current conversion efficiency can reach as high as 91%, which is a record for all quantum-dot-sensitized solar cells. Detailed analysis shows that such an enhancement is due to improved lifetime and diffusion length of electrons in the solar cell. (paper)

Enhanced photovoltaic performance of a quantum dot-sensitized solar cell using a Nb-doped TiO2 electrode.

Science.gov (United States)

Jiang, Lei; You, Ting; Deng, Wei-Qiao

2013-10-18

In this work Nb-doped anatase TiO2 nanocrystals are used as the photoanode of quantum-dot-sensitized solar cells. A solar cell with CdS/CdSe quantum dots co-sensitized 2.5 mol% Nb-doped anatase TiO2 nanocrystals can achieve a photovoltaic conversion efficiency of 3.3%, which is almost twice as high as the 1.7% obtained by a cell based on undoped TiO2 nanocrystals. The incident photon-to-current conversion efficiency can reach as high as 91%, which is a record for all quantum-dot-sensitized solar cells. Detailed analysis shows that such an enhancement is due to improved lifetime and diffusion length of electrons in the solar cell.

Effects of background oxygen pressure on dielectric and ferroelectric properties of epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrTiO3

Science.gov (United States)

Abazari, M.; Akdoǧan, E. K.; Safari, A.

2008-11-01

Oxygen partial pressure (PO_2) in pulsed laser deposition significantly influences the composition, microstructure, and electrical properties of epitaxial misfit strain-relieved 450nm ⟨001⟩ oriented epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated SrTiO3. Films deposited at 400mTorr exhibit high remnant and saturated polarization of 7.5 and 16.5μC /cm2, respectively, which is ˜100% increase over the ones grown at 100mTorr. The dielectric constant linearly increases from 220 to 450 with increasing PO2. The observed changes in surface morphology of the films and their properties are shown to be due to the suppression of volatile A-site cation loss.

Mesostructured niobium-doped titanium oxide-carbon (Nb-TiO2-C) composite as an anode for high-performance lithium-ion batteries

Science.gov (United States)

Hwang, Keebum; Sohn, Hiesang; Yoon, Songhun

2018-02-01

Mesostructured niobium (Nb)-doped TiO2-carbon (Nb-TiO2-C) composites are synthesized by a hydrothermal process for application as anode materials in Li-ion batteries. The composites have a hierarchical porous structure with the Nb-TiO2 nanoparticles homogenously distributed throughout the porous carbon matrix. The Nb content is controlled (0-10 wt%) to investigate its effect on the physico-chemical properties and electrochemical performance of the composite. While the crystalline/surface structure varied with the addition of Nb (d-spacing of TiO2: 0.34-0.36 nm), the morphology of the composite remained unaffected. The electrochemical performance (cycle stability and rate capability) of the Nb-TiO2-C composite anode with 1 wt% Nb doping improved significantly. First, a full cut-off potential (0-2.5 V vs. Li/Li+) of Nb-doped composite anode (1 wt%) provides a higher energy utilization than that of the un-doped TiO2-C anode. Second, Nb-TiO2-C composite anode (1 wt%) exhibits an excellent long-term cycle stability (100% capacity retention, 297 mAh/g at 0.5 C after 100 cycles and 221 mAh/g at 2 C after 500 cycles) and improved rate-capability (192 mAh/g at 5 C), respectively (1 C: 150 mA/g). The superior electrochemical performance of Nb-TiO2-C (1 wt%) could be attributed to the synergistic effect of improved electronic conductivity induced by optimal Nb doping (1 wt%) and lithium-ion penetration (high diffusion kinetics) through unique pore structures.

Ferroelectric properties of NaNbO3-BaTiO3 thin films deposited on SrRuO3/(001)SrTiO3 substrate by pulsed laser deposition

International Nuclear Information System (INIS)

Yamazoe, Seiji; Oda, Shinya; Sakurai, Hiroyuki; Wada, Takahiro; Adachi, Hideaki

2009-01-01

(NaNbO 3 ) 1-x (BaTiO 3 ) x (NN-xBT) thin films with low BaTiO 3 (BT) concentrations x (x=0.05 and 0.10) were fabricated on SrRuO 3 /(001)SrTiO 3 (SRO)/(001)STO) substrate by pulsed laser deposition (PLD). X-ray diffraction pattern (XRD) and transmission electron diffraction pattern (TED) showed that NN-0.10BT thin film was epitaxially grown on SRO/(001)STO substrate with a crystallographic relationship of [001] NN-xBT parallel [001] STO . From reciprocal space maps, the lattice parameters of the out-of-plane direction of NN-xBT thin films became larger with an increase in BT concentration, although the lattice parameter of the in-plane was hardly changed by the BT concentration. The value of relative dielectric constant ε r of the NN-xBT thin films were increased with BT concentration. The ε r and the dielectric loss tanδ of NN-0.10BT were 1220 and 0.02 at 1 kHz, respectively. The P-E hysteresis loops of the NN-xBT thin films showed clear ferroelectricity. Although the value of remanent polarization P r decreased with the BT concentration, the behaviors of ε r , P r , and coercive electric field E c of the NN-xBT thin films against the BT concentration accorded with those of NN-xBT ceramics, in which NN-0.10BT ceramics exhibited the largest piezoelectric property. Therefore, the NN-0.10BT thin film is expected to show high piezoelectricity. (author)

Comparative study of the singularity in the optical properties of congruent doped LiNbO3 crystals

International Nuclear Information System (INIS)

Jaque, F.; Han, T.P.J.; Lifante, G.

2003-01-01

A comparison of the optical properties such as optical absorption band edge, ordinary and extraordinary refractive indices, powder second harmonic generation and the non-linear coefficient, d 33 , of congruent LiNbO 3 crystals doped with di-, tri- and hexa-valent cations is reported. It has been found that the referred parameters show a clear concentration singularity depending on the valency of the cation. A charge compensation mechanism is proposed to explain the role of the cation. The experimental data of n o and n e are described by a generalised Sellmeier equation considering the different ions sites in the crystal

Electric field-induced resistive switching, magnetism, and photoresponse modulation in a Pt/Co0.03Zn0.97O/Nb:SrTiO3 multi-function heterostructure

Science.gov (United States)

Luo, Zhipeng; Pei, Ling; Li, Meiya; Zhu, Yongdan; Xie, Shuai; Cheng, Xiangyang; Liu, Jiaxian; Ding, Huaqi; Xiong, Rui

2018-04-01

A Co0.03Zn0.97O (CZO) thin film was epitaxially grown on a Nb doped (001) SrTiO3 (NSTO) single-crystal substrate by pulsed laser deposition to form a Pt/CZO/NSTO heterostructure. This device exhibits stable bipolar resistive switching, well retention and endurance, multilevel memories, and a resistance ratio of high resistance state (HRS)/low resistance state (LRS) up to 7 × 105. Under the illumination of a 405 nm laser, the HRS of the device showed distinct photoelectricity with an open-circuit voltage of 0.5 V. A stronger ferromagnetism was observed at the HRS than at the LRS. The above phenomenon is attributable to the accumulation and migration of oxygen vacancies at the interface of CZO/NSTO. Our results demonstrated a pathway towards making multifunctional devices that simultaneously exhibit resistive switching, photoelectricity, and ferromagnetism.

Enhanced reducibility and electronic conductivity of Nb or W doped Ce0.9Gd0.1O1.95 - δ

DEFF Research Database (Denmark)

Chatzichristodoulou, Christodoulos; Ricote, Sandrine; Foghmoes, Søren Preben Vagn

2015-01-01

The transport and thermomechanical properties of acceptor (Gd) and donor (Nb or W) co-doped ceria were investigated. The solubility limit of Nb in Ce0.9Gd0.1O2 - δ (CGO10) exceeds 4 at.%, whereas that of W is approximately 2 at.%. Both the thermal and stoichiometric expansion coefficients...... are decreased relative to that of CGO10. Charge compensation of the donor dopants takes place primarily by annihilation of oxide ion vacancies, and a sharp decrease in ionic mobility is observed upon Nb or W doping of CGO10. On the other hand, the n-type electronic conductivity, associated with the reduction...... of Ce4+, increases upon doping with Nb or W, due to enhanced reducibility of cerium. This is beneficial for applications where electronic conductivity is also required, like oxygen permeation membranes. Modeling shows that 4 at.% Nb or W doped CGO10 will deliver higher oxygen fluxes than CGO10, due...

Appearance and disappearance of ferromagnetism in ultrathin LaMnO3 on SrTiO3 substrate: A viewpoint from first principles

Science.gov (United States)

An, Ming; Weng, Yakui; Zhang, Huimin; Zhang, Jun-Jie; Zhang, Yang; Dong, Shuai

2017-12-01

The intrinsic magnetic state (ferromagnetic or antiferromagnetic) of ultrathin LaMnO3 films on the most commonly used SrTiO3 substrate is a long-existing question under debate. Either strain effect or nonstoichiometry was argued to be responsible for the experimental ferromagnetism. In a recent experiment [X. R. Wang, C. J. Li, W. M. Lü, T. R. Paudel, D. P. Leusink, M. Hoek, N. Poccia, A. Vailionis, T. Venkatesan, J. M. D. Coey, E. Y. Tsymbal, Ariando, and H. Hilgenkamp, Science 349, 716 (2015), 10.1126/science.aaa5198], one more mechanism, namely, the self-doping due to polar discontinuity, was argued to be the driving force of ferromagnetism beyond the critical thickness. Here systematic first-principles calculations have been performed to check these mechanisms in ultrathin LaMnO3 films as well as superlattices. Starting from the very precise descriptions of both LaMnO3 and SrTiO3, it is found that the compressive strain is the dominant force for the appearance of ferromagnetism, while the open surface with oxygen vacancies leads to the suppression of ferromagnetism. Within LaMnO3 layers, the charge reconstructions involve many competitive factors and certainly go beyond the intuitive polar catastrophe model established for LaAlO3/SrTiO3 heterostructures. Our paper not only explains the long-term puzzle regarding the magnetism of ultrathin LaMnO3 films but also sheds light on how to overcome the notorious magnetic dead layer in ultrathin manganites.

Above room-temperature ferromagnetism in La1-xCaxMnO3 epitaxial thin films on SrTiO3(001) substrates

Science.gov (United States)

Kou, Yunfang; Wang, Hui; Miao, Tian; Wang, Yanmei; Xie, Lin; Wang, Shasha; Liu, Hao; Lin, Hanxuan; Zhu, Yinyan; Wang, Wenbin; Du, Haifeng; Pan, Xiaoqing; Wu, Ruqian; Yin, Lifeng; Shen, Jian

The colossal magnetoresistive (CMR) manganites are popular materials for spintronics applications due to their high spin polarization. Only a couple of manganites like La1-xSrxMnO3 have a Curie temperature (Tc) that is higher than room temperature. Finding methods to raise the Tc of manganites over room temperature is useful but challenging. In this work, we use the most intensively studied La1-xCaxMnO3 (LCMO) as the prototype system to demonstrate that Tc can be greatly enhanced by carefully tuning the electronic structure using doping and strain. Specifically, we grow LCMO films on SrTiO3 (001) substrates using pulsed laser deposition. Magnetic and transport measurements indicate a great enhancement of Tc over room temperature at x =0.2 doping. Theoretical calculations indicate that the combined effects from doping and strain give rise to a new electronic structure favoring ferromagnetism in LCMO system. Furthermore, using the La0.8Ca0.2MnO3 as ferromagnetic electrodes, we achieve finite tunneling magnetoresistance (TMR) above room temperature.

Growth and electrical properties of (Mn,F) co-doped 0.92Pb(Zn 1/3Nb 2/3)O 3-0.08PbTiO 3 single crystal

Science.gov (United States)

Zhang, Shujun; Lebrun, Laurent; Randall, Clive A.; Shrout, Thomas R.

2004-06-01

The growth and characterization of (Mn,F) doped Pb(Zn 1/3Nb 2/3)O 3-PbTiO 3 (PZNT) single crystals are reported in this paper. The typical single crystal obtained is up to 30 mm size with dark brown color. The crystal lattice parameters of doped PZNT crystal are slightly decreased compared to the pure one. The room temperature dielectric permittivity along direction is about 6000, which is lower than that of the pure PZNT8 because of the dopants. The Curie temperature of the doped crystal is about 180°C while the ferroelectric phase transition temperature is around 100°C, which are higher than those of the pure PZNT8 single crystal. The remnant polarization and coercive field of oriented doped crystal measured at 1 Hz and 10 kV/cm field are about 27 μC/cm 2 and 4.2 kV/cm, respectively. The room temperature mechanical quality factor is ˜300. Piezoelectric coefficient of oriented doped crystal is higher than 3500 pC/N and the longitudinal electromechanical coupling factor is larger than 93%. The piezoelectric properties of doped PZNT single crystal with temperature and orientations are also reported in this paper. The valence state of the manganese dopant was determined by electron spin resonance, indicating no Mn 4+ in the crystals, suggesting the valence of manganese ions in PZNT crystals may be 2+, which acts as a hardener, stabilizes the domain wall and pins the domain wall motion, on the other hand, the dopant will enter Ti 4+ position, shifting the crystal composition to higher PT content.

Phase transitions and optical characterization of lead-free piezoelectric (K0.5Na0.5)0.96Li0.04(Nb 0.8Ta0.2)O3 thin films

KAUST Repository

Yao, Yingbang

2013-06-01

Lead-free piezoelectric thin films, (K0.5Na0.5) 0.96Li0.04(Nb0.8Ta0.2)O 3, were epitaxially grown on MgO(001) and Nb-doped SrTiO 3(001) substrates using pulsed laser deposition. The optimum deposition temperature was found to be 600 C. Two types of in-plane orientations were observed in the films depending on the substrates used. The transmittance and photoluminescence spectra as well as the dielectric and ferroelectric properties of the films were measured. The measured band-gap energy was found to be decreased with the deposition temperature. The dielectric constant decreased from 550 to 300 as the frequency increased from 100 Hz to 1 MHz. The measured remnant polarization and coercive field were 4 μC/cm2 and 68 kV/cm, respectively. The phase transitions of the films were studied by Raman spectroscopy. Two distinct anomalies originating from the cubic-to-tetragonal (TC-T ~ 300 C) and tetragonal-to-orthorhombic (TT-O ~ 120 C) phase transitions were observed. Our results show that Raman spectroscopy is a powerful tool in identifying the phase transitions in ferroelectric thin films. © 2013 Elsevier B.V.

Performance evaluation of Mn and Fe doped SrCo0.9Nb0.1O3-δ cathode for IT-SOFC application

Science.gov (United States)

Bele, Lokesh; Lenka, R. K.; Patro, P. K.; Muhmood, L.; Mahata, T.; Sinha, P. K.

2018-02-01

Cathode materials of Mn and Fe doped SrCo0.9Nb0.1O3-δ, are synthesized by solid state route for intermediate temperature fuel cell applications. Phase pure material is obtained after calcining the precursors at 1100 °C. Phase compatibility is observed between this novel cathode material with gadolinia doped ceria (GDC) electrolyte material as reflected in the diffraction pattern. The state of art YSZ electrolyte is not compatible with this cathode material. Average thermal expansion coefficient of the material varies between 17 to 22 X 10-6 K-1 on doping, from room temperature to 800 °C. Increase in thermal expansion coefficient is observed with Mn and Fe doping associated with the loss of oxygen from the crystal. The electrical conductivity of the cathode material decreases with Fe and Mn doping. Mn doped samples show lowest conductivity. From the symmetric cell measurement lower area specific resistance (0.16 Ω-cm2) is obtained for un-doped samples, at 850 °C. From the initial results it can be inferred that Mn/Fe doping improves neither the thermal expansion co-efficient nor the electrochemical activity.

Optical temperature sensing by upconversion luminescence of Er doped Bi5TiNbWO15ferroelectric materials

Directory of Open Access Journals (Sweden)

Hua Zou

2014-12-01

Full Text Available The Er3+ doped Bi5TiNbWO15 ceramics have been synthesized using conventional solid-state reaction techniques. The crystal structure, ferroelectric properties, UC emission properties and especially the temperature sensing behaviors were systematically studied. With increasing Er3+ content, the investigation of XRD pattern, the ferroelectric loop and the UC emission indicated that the Er3+ ions dopants preferentially substituted the A sites of Bi3TiNbO9 and then Bi2WO6. Based on fluorescence intensity ratio (FIR technique, the observed results implied the ceramics were promising candidates for temperature sensors in the temperature range of 175 K −550 K. More importantly, this study provided a contrast of temperature sensitivity between emission from the same part (Bi3TiNbO9 in bismuth layered-structure and emission from the different part (Bi3TiNbO9 and Bi2WO6 in bismuth layered-structure for the first time.

Thermodynamics of superconducting Nb3Al, Nb3Ge, Nb3Sn, and V3Ga

Science.gov (United States)

Mitrović, B.; Schachinger, E.; Carbotte, J. P.

1984-06-01

We have calculated the superconducting thermodynamic properties for several high-transition-temperature A15 compounds: Nb-Al, Nb-Ge, Nb-Sn, and V-Ga. In our calculations we have used the tunneling electron-phonon-coupling spectra α2F for all four systems considered, and in the case of Nb-Al and Nb-Ge we have also used α2F=CG, where G is the measured generalized phonon density of states and C is a constant. We find that all Nb-based A15 compounds display similar thermodynamic properties, which do not depend explicitly on the band density of states: 2Δ0κBTc≅4.6, ΔCγTc≅2.5-2.6,-Tc[dHc(T)dT]TcHc(0)≅2.1, γ[TcHc(0)]2≅0.134, and positive D(t)'s with the maximum value around 0.02. For Nb3Sn we find good agreement between the calculated properties and the old specific-heat experimental results (γ≅52 mJ/mol K2). The same applies to V3Ga, where the theoretical results have been compared with the experiments of Junod et al. However, we do not find good agreement between calculated ΔCγTc, - Tc[dHc(T)dT]TcHc(0), γ[TcHc(0)]2, and experimental values for Nb3Al and Nb3Ge, presumably due to broadened transitions. It is argued that the tunneling experiments underestimate the value of the gap which should be associated with the inverted α2F.

Hole localization, migration, and the formation of peroxide anion in perovskite SrTiO3

Science.gov (United States)

Chen, Hungru; Umezawa, Naoto

2014-07-01

Hybrid density functional calculations are carried out to investigate the behavior of holes in SrTiO3. As in many other oxides, it is shown that a hole tend to localize on one oxygen forming an O- anion with a concomitant lattice distortion; therefore a hole polaron. The calculated emission energy from the recombination of the localized hole and a conduction-band electron is about 2.5 eV, in good agreement with experiments. Therefore the localization of the hole or self-trapping is likely to be responsible for the green photoluminescence at low temperature, which was previously attributed to an unknown defect state. Compared to an electron, the calculated hole polaron mobility is three orders of magnitude lower at room temperature. In addition, two O- anions can bind strongly to form an O22- peroxide anion. No electronic states associated with the O22- peroxide anion are located inside the band gap or close to the band edges, indicating that it is electronically inactive. We suggest that in addition to the oxygen vacancy, the formation of the O22- peroxide anion can be an alternative to compensate acceptor doping in SrTiO3.

Properties of Nb-doped ZnO transparent conductive thin films ...

Indian Academy of Sciences (India)

Administrator

by rf magnetron sputtering using a high quality ceramic target ... Guangxi Key Laboratory of Information Materials, Guilin University of Electronic ... films are highly textured along the c axis and perpendicular to the surface of the substrate. ... ZnO films; Nb-doped; magnetron sputtering; optical and electrical properties. 1.

Oxidation-resistant Ge-doped silicide coating on Cr-Cr2Nb alloys by pack cementation

International Nuclear Information System (INIS)

He Yirong

1997-01-01

The halide-activated pack cementation process was modified to produce a Ge-doped silicide diffusion coating on Cr-Cr 2 Nb alloys in a single processing step. The morphology and composition of the coating depended both on the pack composition and processing schedule and also on the composition and microstructure of the substrate. Higher Ge content in the pack suppressed the formation of CrSi 2 and reduced the growth kinetics of the coating. Ge was not homogeneously distributed in the coatings. Under cyclic and isothermal oxidation conditions, the Ge-doped silicide coating protected the Cr-Nb alloys from significant oxidation and from pesting by the formation of a Ge-doped silica film. (orig.)

Ion channeling study of lattice distortions in chromium-doped SrTiO3 crystals

Czech Academy of Sciences Publication Activity Database

Lavrentiev, Vasyl; Vacík, Jiří; Dejneka, Alexandr; Trepakov, Vladimír; Jastrabík, Lubomír

2013-01-01

Roč. 55, č. 7 (2013), s. 1431-1437 ISSN 1063-7834 R&D Projects: GA ČR(CZ) GAP107/11/1856; GA ČR(CZ) GBP108/12/G108; GA ČR GAP108/12/1941 Grant - others:GA MŠk(CZ) ED2.1.00/03.0058 Program:ED Institutional support: RVO:68378271 ; RVO:61389005 Keywords : ion channeling * lattice distortions * SrTiO3 Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders; BM - Solid Matter Physics ; Magnetism (FZU-D) Impact factor: 0.782, year: 2013 http://link.springer.com/article/10.1134%2FS1063783413070202

Evolution of electrical properties and domain configuration of Mn modified Pb(In1/2Nb1/2)O3-PbTiO3 single crystals

Science.gov (United States)

Qiao, Huimin; He, Chao; Yuan, Feifei; Wang, Zujian; Li, Xiuzhi; Liu, Ying; Guo, Haiyan; Long, Xifa

2018-04-01

The acceptor doped relaxor-based ferroelectric materials are useful for high power applications such as probes in ultrasound-guided high intensity focused ultrasound therapy. In addition, a high Curie temperature is desired because of wider temperature usage and improved temperature stability. Previous investigations have focused on Pb(Mg1/3Nb2/3)O3-PbTiO3 and Pb(Zn1/3Nb2/3)O3-PbTiO3 systems, which have a ultrahigh piezoelectric coefficient and dielectric constant, but a relatively low Curie temperature. It is desirable to study the binary relaxor-based system with a high Curie temperature. Therefore, Pb(In1/2Nb1/2)O3-PbTiO3 (PINT) single crystals were chosen to study the Mn-doped influence on their electrical properties and domain configuration. The evolution of ferroelectric hysteresis loops for doped and virgin samples exhibit the pinning effect in Mn-doped PINT crystals. The relaxation behaviors of doped and virgin samples are studied by fit of the modified Curie-Weiss law and Volgel-Fucher relation. In addition, a short-range correlation length was fitted to study the behavior of polar nanoregions based on the domain configuration obtained by piezoresponse force microscopy. Complex domain structures and smaller short-range correlation lengths (100-150 nm for Mn-doped PINT and >400 nm for pure PINT) were obtained in the Mn-doped PINT single crystals.

Ferroelectric BaTiO3 and LiNbO3 Nanoparticles Dispersed in Ferroelectric Liquid Crystal Mixtures: Electrooptic and Dielectric (Postprint)

Science.gov (United States)

2016-10-14

strength for non- doped LF4 and LiNbO3/LF4 nanocolloids at temperature 30C. 146 R. K . SHUKLA ET AL. 6 Distribution A. Approved for public release (PA...AFRL-RX-WP-JA-2017-0210 FERROELECTRIC BaTiO3 AND LiNbO3 NANOPARTICLES DISPERSED IN FERROELECTRIC LIQUID CRYSTAL MIXTURES: ELECTROOPTIC...COMMAND UNITED STATES AIR FORCE Ferroelectric BaTiO3 and LiNbO3 nanoparticles dispersed in ferroelectric liquid crystal mixtures: Electrooptic and

Influence of La doping on structural and dielectric properties of SrBi2Nb2O9 ceramics

Science.gov (United States)

Verma, Maya; Sreenivas, K.; Gupta, Vinay

2009-01-01

Lanthanum doped SrBi2Nb2O9 ceramics with the chemical formula SrBi2-xLaxNb2O9 (SBLN) (x =0-0.5) have been prepared through conventional solid state route. X-ray diffraction reveals the shrinkage of unit cell of strontium bismuth niobate with incorporation of La3+ dopant, having no lone pair electrons. Shifting of Raman phonon modes indicates the reduced rattling space of NbO6 octahedra with increase in La doping concentration. Further, the softening of lowest frequency phonon mode with increasing x in SBLN shows the transition from ferroelectric to paraelectric at room temperature. The dielectric properties for all the compositions are studied as a function of temperature (25 to 500 °C) over the frequency range of 10 kHz-1 MHz. With increase in lanthanum doping concentration the phase transition becomes diffused and transition temperature gets shifted toward lower temperature. A phase transition from normal ferroelectric to paraelectric has been observed via relaxor-type ferroelectrics with increase in x. The frequency dependence of transition temperature was studied in terms of Vogel-Fulcher relation for SBLN (x =0.4).

Influence of La doping on structural and dielectric properties of SrBi2Nb2O9 ceramics

International Nuclear Information System (INIS)

Verma, Maya; Sreenivas, K.; Gupta, Vinay

2009-01-01

Lanthanum doped SrBi 2 Nb 2 O 9 ceramics with the chemical formula SrBi 2-x La x Nb 2 O 9 (SBLN) (x=0-0.5) have been prepared through conventional solid state route. X-ray diffraction reveals the shrinkage of unit cell of strontium bismuth niobate with incorporation of La 3+ dopant, having no lone pair electrons. Shifting of Raman phonon modes indicates the reduced rattling space of NbO 6 octahedra with increase in La doping concentration. Further, the softening of lowest frequency phonon mode with increasing x in SBLN shows the transition from ferroelectric to paraelectric at room temperature. The dielectric properties for all the compositions are studied as a function of temperature (25 to 500 deg. C) over the frequency range of 10 kHz-1 MHz. With increase in lanthanum doping concentration the phase transition becomes diffused and transition temperature gets shifted toward lower temperature. A phase transition from normal ferroelectric to paraelectric has been observed via relaxor-type ferroelectrics with increase in x. The frequency dependence of transition temperature was studied in terms of Vogel-Fulcher relation for SBLN (x=0.4)

Sorption of U(VI) in surfaces of SrTiO3

International Nuclear Information System (INIS)

Ortiz O, H.B.; Ordonez R, E.; Fernandez V, S.M.

2004-01-01

In this work is presented the physico chemical characterization and evaluation of those surface properties and of sorption of U on the SrTiO 3 like possible candidate for contention barrier in the deep geological confinement. The made studies showed that the SrTiO 3 presents maximum levels of sorption of positive nature species (mainly UO 2 2+ and UO 2 NO 3 + ). (Author)

Resistance change effect in SrTiO3/Si (001) isotype heterojunction

Science.gov (United States)

Huang, Xiushi; Gao, Zhaomeng; Li, Pei; Wang, Longfei; Liu, Xiansheng; Zhang, Weifeng; Guo, Haizhong

2018-02-01

Resistance switching has been observed in double and multi-layer structures of ferroelectric films. The higher switching ratio opens up a vast path for emerging ferroelectric semiconductor devices. An n-n+ isotype heterojunction has been fabricated by depositing an oxide SrTiO3 layer on a conventional n-type Si (001) substrate (SrTiO3/Si) by pulsed laser disposition. Rectification and resistive switching behaviors in the n-n+ SrTiO3/Si heterojunction were observed by a conductive atomic force microscopy, and the n-n+ SrTiO3/Si heterojunction exhibits excellent endurance and retention characteristics. The possible mechanism was proposed based on the band structure of the n-n+ SrTiO3/Si heterojunction, and the observed electrical behaviors could be attributed to the modulation effect of the electric field reversal on the width of accumulation and the depletion region, as well as the height of potential of the n-n+ junction formed at the STO/Si interface. Moreover, oxygen vacancies are also indicated to play a crucial role in causing insulator to semiconductor transition. These results open the way to potential application in future microelectronic devices based on perovskite oxide layers on conventional semiconductors.

Thermodynamics of superconducting Nb3Al, Nb3Ge, Nb3Sn, and V3Ga

International Nuclear Information System (INIS)

Mitrovic, B.; Schachinger, E.; Carbotte, J.P.

1984-01-01

We have calculated the superconducting thermodynamic properties for several high-transition-temperature A15 compounds: Nb-Al, Nb-Ge, Nb-Sn, and V-Ga. In our calculations we have used the tunneling electron-phonon--coupling spectra α 2 F for all four systems considered, and in the case of Nb-Al and Nb-Ge we have also used α 2 F = CG, where G is the measured generalized phonon density of states and C is a constant. We find that all Nb-based A15 compounds display similar thermodynamic properties, which do not depend explicitly on the band density of states: 2Δ 0 /k/sub B/T/sub c/approx. =4.6, ΔC/γT/sub c/approx. =2.5--2.6, -T/sub c/[dH/sub c/(T)/dT]c/ H/sub c/(0)approx. =2.1, γ[T/sub c//H/sub c/(0)] 2 approx. =0.134, and positive D(t)'s with the maximum value around 0.02. For Nb 3 Sn we find good agreement between the calculated properties and the old specific-heat experimental results (γapprox. =52 mJ/mol K 2 ). The same applies to V 3 Ga, where the theoretical results have been compared with the experiments of Junod et al. However, we do not find good agreement between calculated ΔC/γT/sub c/, -T/sub c/[dH/sub c/(T)/dT]c/H/sub c/(0), γ[T/sub c//H/sub c/(0)] 2 , and experimental values for Nb 3 Al and Nb 3 Ge, presumably due to broadened transitions. It is argued that the tunneling experiments underestimate the value of the gap which should be associated with the inverted α 2 F

Nonvolatile resistive switching in Pt/laALO3/srTiO3 heterostructures

KAUST Repository

Wu, S.

2013-12-12

Resistive switching heterojunctions, which are promising for nonvolatile memory applications, usually share a capacitorlike metal-oxide-metal configuration. Here, we report on the nonvolatile resistive switching in Pt/LaAlO3/SrTiO3 heterostructures, where the conducting layer near the LaAlO3/SrTiO3 interface serves as the "unconventional"bottom electrode although both oxides are band insulators. Interestingly, the switching between low-resistance and high-resistance states is accompanied by reversible transitions between tunneling and Ohmic characteristics in the current transport perpendicular to the planes of the heterojunctions. We propose that the observed resistive switching is likely caused by the electric-field-induced drift of charged oxygen vacancies across the LaAlO3/SrTiO3 interface and the creation of defect-induced gap states within the ultrathin LaAlO3 layer. These metal-oxide-oxide heterojunctions with atomically smooth interfaces and defect-controlled transport provide a platform for the development of nonvolatile oxide nanoelectronics that integrate logic and memory devices.

Epitaxial growth of SrTiO3 thin film on Si by laser molecular beam epitaxy

International Nuclear Information System (INIS)

Zhou, X. Y.; Miao, J.; Dai, J. Y.; Chan, H. L. W.; Choy, C. L.; Wang, Y.; Li, Q.

2007-01-01

SrTiO 3 thin films have been deposited on Si (001) wafers by laser molecular beam epitaxy using an ultrathin Sr layer as the template. X-ray diffraction measurements indicated that SrTiO 3 was well crystallized and epitaxially aligned with Si. Cross-sectional observations in a transmission electron microscope revealed that the SrTiO 3 /Si interface was sharp, smooth, and fully crystallized. The thickness of the Sr template was found to be a critical factor that influenced the quality of SrTiO 3 and the interfacial structure. Electrical measurements revealed that the SrTiO 3 film was highly resistive

Photocatalytic degradation of malachite green dye using Au/NaNbO_3 nanoparticles

International Nuclear Information System (INIS)

Baeissa, E.S.

2016-01-01

The morphology of sodium niobate, which was produced using a hydrothermal method, was studied by changing the hydrothermal temperature from 100 to 250 °C. Using 250 °C hydrothermal temperature resulted in sodium niobate with a nanocube structure. The sodium niobate nanocubes were doped with gold by impregnation with an aqueous solution of HAuCl_4. The band gap of sodium niobate is approximately 3.4 eV, and it was decreased to 2.45 eV by gold doping. The surface area of sodium niobate is higher than that of Au/NaNbO_3 due to blockage of some pores of sodium niobate by gold doping. The photocatalytic performance of gold-doped sodium niobate was studied by degradation of malachite green dye using visible light irradiation. The results demonstrate that the photocatalytic performance of gold-doped sodium niobate is higher than that of sodium niobate and TiO_2 Degussa under visible light irradiation. - Highlights: • Au/NaNbO_3 were used for photocatalytic degradation of malachite green dye. • Photocatalytic degradation was dependent on wt % of Au; reaction time, and weight of catalyst. • Catalyst re-use revealed the present photocatalyst remain effective and active after five cycles.

Dual-enhancement of ferro-/piezoelectric and photoluminescent performance in Pr{sup 3+} doped (K{sub 0.5}Na{sub 0.5})NbO{sub 3} lead-free ceramics

Energy Technology Data Exchange (ETDEWEB)

Wei, Yongbin; Jia, Yanmin, E-mail: wuzheng@zjnu.cn, E-mail: ymjia@zjnu.edu.cn; Wu, Jiang; Shen, Yichao [Department of Physics, Zhejiang Normal University, Jinhua 321004 (China); Wu, Zheng, E-mail: wuzheng@zjnu.cn, E-mail: ymjia@zjnu.edu.cn [College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua 321004 (China); Luo, Haosu [Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800 (China)

2014-07-28

A mutual enhancement action between the ferro-/piezoelectric polarization and the photoluminescent performance of rare earth Pr{sup 3+} doped (K{sub 0.5}Na{sub 0.5})NbO{sub 3} (KNN) lead-free ceramics is reported. After Pr{sup 3+} doping, the KNN ceramics exhibit the maximum enhancement of ∼1.2 times in the ferroelectric remanent polarization strength and ∼1.25 times in the piezoelectric coefficient d{sub 33}, respectively. Furthermore, after undergoing a ferro-/piezoelectric polarization treatment, the maximum enhancement of ∼1.3 times in photoluminescence (PL) was observed in the poled 0.3% Pr{sup 3+} doped sample. After the trivalent Pr{sup 3+} unequivalently substituting the univalent (K{sub 0.5}Na{sub 0.5}){sup +}, A-sites ionic vacancies will occur to maintain charge neutrality, which may reduce the inner stress and ease the domain wall motions, yielding to the enhancement in ferro-/piezoelectric performance. The polarization-induced enhancement in PL is attributed to the decrease of crystal symmetry abound the Pr{sup 3+} ions after polarization. The dual-enhancement of the ferro-/piezoelectric and photoluminescent performance makes the Pr{sup 3+} doped KNN ceramic hopeful for piezoelectric/luminescent multifunctional devices.

Contributions of conduction band offset to the enhanced separation efficiency of photoinduced charges for SrTiO3/Bi2O3 heterojunction semiconductor

International Nuclear Information System (INIS)

Zhang, Zhenlong; Zhu, Jichun; Li, Shengjun; Mao, Yanli

2014-01-01

SrTiO 3 /Bi 2 O 3 heterojunction semiconductor was prepared and characterized by X-ray diffraction, UV–vis absorption spectrum, and scanning electron microscope, surface photovoltage spectroscopy, and photoluminescence spectroscopy. The surface photovoltage spectra indicate that the separation efficiency of photoinduced charges for SrTiO 3 /Bi 2 O 3 was enhanced compared with that of SrTiO 3 or Bi 2 O 3 . The energy band diagram of SrTiO 3 /Bi 2 O 3 heterojunction was directly determined with X-ray photoelectron spectroscopy, and the conduction band offset between SrTiO 3 and Bi 2 O 3 was quantified to be 0.28±0.03 eV. The photoluminescence spectra display that the recombination rate of photoinduced carriers for SrTiO 3 /Bi 2 O 3 decreases compared with that of SrTiO 3 or Bi 2 O 3 , which is mainly due to the energy levels matching between them. Therefore the enhanced separation efficiency of photoinduced charges is resulting from the energy difference between the conduction band edges of SrTiO 3 and Bi 2 O 3 . -- Graphical abstract: Enhanced separation efficiency for SrTiO 3 /Bi 2 O 3 is resulting from the energy difference between the conduction band edges. Highlights: ●Heterojunction semiconductor of SrTiO 3 /Bi 2 O 3 was prepared. ●SrTiO 3 /Bi 2 O 3 presents enhanced separation efficiency. ●Conduction band offset between SrTiO 3 and Bi 2 O 3 is quantified. ●Recombination rate of SrTiO 3 /Bi 2 O 3 decreases compared with single phases

Investigation of Mn Implanted LiNbO3 applying electron paramagnetic resonance technique

International Nuclear Information System (INIS)

Darwish, A.; Ila, D.; Poker, D.B.; Hensley, D.K.

1997-10-01

The effect of ion implantation on the LiNbO 3 crystal is studied using electron paramagnetic resonance spectroscopy (EPR). EPR measurements on these crystals were performed as a function of ion species Mn and Fe and fluence at room temperature. Also the effect of the laser illumination on the EPR signal was determined by illuminating the crystal in situ and measuring the decay and growth of the EPR signal. LiNbO 3 :Mn 2+ at a depth of approximately 200 nm was formed by implantation of 2.5 x 10 14 Mncm 2 and 1 x 10 17 Mn/cm 2 at 2 MeV. The implanted samples were compared with bulk doped crystals. It was found that the decay and growth of Mn EPR for the implanted crystal is very small compared with the bulk doped LiNbO 3 :Mn crystal. This was found to be primarily due to the spin concentration on the crystals. On the other, hand the decay time of the high fluence is about 40% slower than the decay of the low fluence implanted crystal

Effects of Nb impurity on orthorhombic PbZrO3 crystals

International Nuclear Information System (INIS)

Rivera, Richard; Stashans, Arvids

2008-01-01

A study of Nb doping in lead zirconate (PbZrO 3 ) has been carried out by using a quantum-chemical method developed for crystals and a periodic supercell model. One of the Zr atoms was replaced by an Nb atom in the supercell consisting of 80 atoms. The obtained geometry optimization for the defective region points to defect-outward atomic movements, which are accompanied by some reduction of atomic charges. It is observed that an extra electron imposed by the Nb impurity is transferred to the conduction band of the material and contributes to the n-type electrical conductivity, explaining indirectly some of the experimental observations.

Tailoring the surface chemical bond states of the NbN films by doping Ag: Achieving hard hydrophobic surface

Energy Technology Data Exchange (ETDEWEB)

Ren, Ping; Zhang, Kan; Du, Suxuan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun, 130012 (China); Meng, Qingnan [College of Construction Engineering, Jilin University, Changchun, 130026 (China); He, Xin [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun, 130012 (China); Wang, Shuo [Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871 (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); Zheng, Weitao, E-mail: WTZheng@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)

2017-06-15

Highlights: • Intrinsically hydrophilic NbN films can transfer to hydrophobic Nb-Ag-N films by doping Ag atoms into NbN sublattice. • Solute Ag can promote that the hydrophobic Ag{sub 2}O groups formed on the Nb-Ag-N film surface through self-oxidation. • The present work may provide a straightforward approach for the production of robust hydrophobic ceramic surfaces. - Abstract: Robust hydrophobic surfaces based on ceramics capable of withstanding harsh conditions such as abrasion, erosion and high temperature, are required in a broad range of applications. The metal cations with coordinative saturation or low electronegativity are commonly chosen to achieve the intrinsically hydrophobic ceramic by reducing Lewis acidity, and thus the ceramic systems are limited. In this work, we present a different picture that robust hydrophobic surface with high hardness (≥20 GPa) can be fabricated through doping Ag atoms into intrinsically hydrophilic ceramic film NbN by reactive co-sputtering. The transition of wettability from hydrophilic to hydrophobic of Nb-Ag-N films induced by Ag doping results from the appearance of Ag{sub 2}O groups on the films surfaces through self-oxidation, because Ag cations (Ag{sup +}) in Ag{sub 2}O are the filled-shell (4d{sup 10}5S{sup 0}) electronic structure with coordinative saturation that have no tendency to interact with water. The results show that surface Ag{sub 2}O benefited for hydrophobicity comes from the solute Ag atoms rather than precipitate metal Ag, in which the more Ag atoms incorporated into Nb-sublattice are able to further improve the hydrophobicity, whereas the precipitation of Ag nanoclusters would worsen it. The present work opens a window for fabricating robust hydrophobic surface through tailoring surface chemical bond states by doping Ag into transition metal nitrides.

Electric field effects in graphene/LaAlO3/SrTiO3 heterostructures and nanostructures

Directory of Open Access Journals (Sweden)

Mengchen Huang

2015-06-01

Full Text Available We report the development and characterization of graphene/LaAlO3/SrTiO3 heterostructures. Complex-oxide heterostructures are created by pulsed laser deposition and are integrated with graphene using both mechanical exfoliation and transfer from chemical-vapor deposition on ultraflat copper substrates. Nanoscale control of the metal-insulator transition at the LaAlO3/SrTiO3 interface, achieved using conductive atomic force microscope lithography, is demonstrated to be possible through the graphene layer. LaAlO3/SrTiO3-based electric field effects using a graphene top gate are also demonstrated. The ability to create functional field-effect devices provides the potential of graphene-complex-oxide heterostructures for scientific and technological advancement.

Stability and electronic structure studies of LaAlO3/SrTiO3 (110) heterostructures

International Nuclear Information System (INIS)

Du Yan-Ling; Wang Chun-Lei; Li Ji-Chao; Xu Pan-Pan; Zhang Xin-Hua; Liu Jian; Su Wen-Bin; Mei Liang-Mo

2014-01-01

The first-principles calculations are employed to investigate the stability, magnetic, and electrical properties of the oxide heterostructure of LaAlO 3 /SrTiO 3 (110). By comparing their interface energies, it is obtained that the buckled interface is more stable than the abrupt interface. This result is consistent with experimental observation. At the interface of LaAlO 3 /SrTiO 3 (110) heterostructure, the Ti—O octahedron distortions cause the Ti t 2g orbitals to split into the two-fold degenerate d xz /d yz and nondegenerate d xy orbitals. The former has higher energy than the latter. The partly filled two-fold degenerate t 2g orbitals are the origin of two-dimensional electron gas, which is confined at the interface. Lattice mismatch between LaAlO 3 and SrTiO 3 leads to ferroelectric-like lattice distortions at the interface, and this is the origin of spin-splitting of Ti 3d electrons. Hence the magnetism appears at the interface of LaAlO 3 /SrTiO 3 (110). (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Conductivity and structure of sub-micrometric SrTiO3-YSZ composites

DEFF Research Database (Denmark)

Ruiz Trejo, Enrique; Thydén, Karl Tor Sune; Bonanos, Nikolaos

2016-01-01

Sub-micrometric composites of SrTiO3-YSZ (1:1 volume) and samples of SrTiO3 were prepared by high temperature consolidation of precursors obtained by precipitation with NaOH. The structure development and morphology of the precursors were studied by XRD and SEM. The perovskite and fluorite phases...... in the composites are clearly formed at 600°C with no signs of reaction up to 1100°C; the nominally pure SrTiO3 can be formed at temperatures as low as 400°C. Composites with sub-micrometric grain sizes can be prepared successfully without reaction between the components, although a change in the cell parameter...... of the SrTiO3 is attributed to the presence of Na. The consolidated composites were studied by impedance spectroscopy between 200 and 400°C and at a fixed temperature of 600°C with a scan in the partial pressure of oxygen. The composites did not exhibit high levels of ionic conductivity in the grain...

Physics of SrTiO3-based heterostructures and nanostructures: a review.

Science.gov (United States)

Pai, Yun-Yi; Tylan-Tyler, Anthony; Irvin, Patrick; Levy, Jeremy

2018-02-09

This review provides a summary of the rich physics expressed within SrTiO 3 -based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO 3 itself, we will then discuss the basics of SrTiO 3 -based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.

Physics of SrTiO3-based heterostructures and nanostructures: a review

Science.gov (United States)

Pai, Yun-Yi; Tylan-Tyler, Anthony; Irvin, Patrick; Levy, Jeremy

2018-03-01

This review provides a summary of the rich physics expressed within SrTiO3-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO3 itself, we will then discuss the basics of SrTiO3-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.

The changes of capacitance-loss and current-voltage characteristics of LaMnO3+δ/SrTiO3:Nb heterojunctions exposed to ambient air

International Nuclear Information System (INIS)

Cui Yimin; Wang Rongming

2010-01-01

Effects of moisture absorption on capacitance-loss and current-voltage characteristics of LaMnO 3+δ /SrTiO 3 :Nb heterojunction had been investigated after the heterojunctions were exposed to ambient air. The moisture-absorption-induced increases in loss tangent and breakdown voltage were observed, whereas no changes were found on capacitance and diffusion voltage. These results were discussed by the decrease of oxygen ions in LaMnO 3+δ and the generation of hydroxide ions at grain boundaries. This work will favor both electronic transport analysis and future device applications.

Magnetic two-dimensional electron gas at the manganite-buffered LaAlO3/SrTiO3 interface

DEFF Research Database (Denmark)

R. Zhang, H.; Zhang, Y.; Zhang, H.

2017-01-01

Fabrication of highly mobile spin-polarized two-dimensional electron gas (2DEG) is crucially important for both fundamental and applied research. Usually, spin polarization appears below 10 K for the 2DEG of LaAlO3/SrTiO3 interface, stemming from the magnetic ordering of Ti3+ ions with the mediat......Fabrication of highly mobile spin-polarized two-dimensional electron gas (2DEG) is crucially important for both fundamental and applied research. Usually, spin polarization appears below 10 K for the 2DEG of LaAlO3/SrTiO3 interface, stemming from the magnetic ordering of Ti3+ ions...... with the mediation of itinerant electrons. Herein, we report a magnetic 2DEG at a La7/8Sr1/8MnO3-buffered LaAlO3/SrTiO3 interface, which simultaneously shows electrically tunable anomalous Hall effect and high conductivity. The spin-polarized temperature for the 2DEG is promoted to 30 K while the mobility remains...... high. The magnetism likely results from a gradient manganese interdiffusion into SrTiO3. The present work demonstrates the great potential of manganite-buffered LaAlO3/SrTiO3 interfaces for spintronic applications....

Modification of SrTiO3 single-crystalline surface after plasma flow treatment

Energy Technology Data Exchange (ETDEWEB)

Levin, Alexandr A.; Weissbach, Torsten; Leisegang, Tilmann; Meyer, Dirk C. [Institut fuer Strukturphysik, Technische Universitaet Dresden, 01062 Dresden (Germany); Kulagin, Nikolay A. [Kharkiv National University for Radioelectronics, av. Shakespeare 6-48, 61045 Kharkiv (Ukraine); Langer, Enrico [Institut fuer Festkoerperphysik, Technische Universitaet Dresden, 01062 Dresden (Germany)

2009-07-01

Surface of pure and transition metal-doped SrTiO3(STO) single crystals before and after hydrogen plasma-flow treatment (energy of 5..20 J/cm2) is investigated by wide-angle X-ray diffraction (WAXRD), fluorescence X-ray absorption near edge structure (XANES) and scanning electron microscopy (SEM) techniques. Plasma treatment results in the formation of a textured polycrystalline layer at the surface of the single-crystalline samples with different orientation. The formation of the quasi-ordered structures consisting of nanoscale-sized pyramids is observed by SEM. XANES evidences the change of the valency of the part of Ti4+ to Ti3+ due to the plasma treatment. The data obtained together with results of X-ray spectroscopy measurements gives evidences of the change of stoichiometry of the STO samples resulting in a change of their physical properties after plasma treatment.

Efficiency of Nb-Doped ZnO Nanoparticles Electrode for Dye-Sensitized Solar Cells Application

Science.gov (United States)

Anuntahirunrat, Jirapat; Sung, Youl-Moon; Pooyodying, Pattarapon

2017-09-01

The technological of Dye-sensitized solar cells (DSSCs) had been improved for several years. Due to its simplicity and low cost materials with belonging to the part of thin films solar cells. DSSCs have numerous advantages and benefits among the other types of solar cells. Many of the DSSC devices had use organic chemical that produce by specific method to use as thin film electrodes. The organic chemical that widely use to establish thin film electrodes are Zinc Oxide (ZnO), Titanium Dioxide (TiO2) and many other chemical substances. Zinc oxide (ZnO) nanoparticles had been used in DSSCs applications as thin film electrodes. Nanoparticles are a part of nanomaterials that are defined as a single particles 1-100 nm in diameter. From a few year ZnO widely used in DSSC applications because of its optical, electrical and many others properties. In particular, the unique properties and utility of ZnO structure. However the efficiency of ZnO nanoparticles based solar cells can be improved by doped various foreign impurity to change the structures and properties. Niobium (Nb) had been use as a dopant of metal oxide thin films. Using specification method to doped the ZnO nanoparticles thin film can improved the efficiencies of DSSCs. The efficiencies of Nb-doped ZnO can be compared by doping 0 at wt% to 5 at wt% in ZnO nanoparticles thin films that prepared by the spin coating method. The thin film electrodes doped with 3 at wt% represent a maximum efficiencies with the lowest resistivity of 8.95×10-4 Ω·cm.

Nonvolatile Resistive Switching in Pt/LaAlO_{3}/SrTiO_{3} Heterostructures

Directory of Open Access Journals (Sweden)

Shuxiang Wu

2013-12-01

Full Text Available Resistive switching heterojunctions, which are promising for nonvolatile memory applications, usually share a capacitorlike metal-oxide-metal configuration. Here, we report on the nonvolatile resistive switching in Pt/LaAlO_{3}/SrTiO_{3} heterostructures, where the conducting layer near the LaAlO_{3}/SrTiO_{3} interface serves as the “unconventional” bottom electrode although both oxides are band insulators. Interestingly, the switching between low-resistance and high-resistance states is accompanied by reversible transitions between tunneling and Ohmic characteristics in the current transport perpendicular to the planes of the heterojunctions. We propose that the observed resistive switching is likely caused by the electric-field-induced drift of charged oxygen vacancies across the LaAlO_{3}/SrTiO_{3} interface and the creation of defect-induced gap states within the ultrathin LaAlO_{3} layer. These metal-oxide-oxide heterojunctions with atomically smooth interfaces and defect-controlled transport provide a platform for the development of nonvolatile oxide nanoelectronics that integrate logic and memory devices.

Metallic and Insulating Interfaces of Amorphous SrTiO3-Based Oxide Heterostructures

DEFF Research Database (Denmark)

Chen, Yunzhong; Pryds, Nini; Kleibeuker, Josée E.

2011-01-01

AlO3, SrTiO3, and yttria-stabilized zirconia films. On the other hand, samples of amorphous La7/8Sr1/8MnO3 films on SrTiO3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface...

Photocatalytic degradation of malachite green dye using Au/NaNbO{sub 3} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Baeissa, E.S., E-mail: elhambaeissa@gmail.com

2016-07-05

The morphology of sodium niobate, which was produced using a hydrothermal method, was studied by changing the hydrothermal temperature from 100 to 250 °C. Using 250 °C hydrothermal temperature resulted in sodium niobate with a nanocube structure. The sodium niobate nanocubes were doped with gold by impregnation with an aqueous solution of HAuCl{sub 4}. The band gap of sodium niobate is approximately 3.4 eV, and it was decreased to 2.45 eV by gold doping. The surface area of sodium niobate is higher than that of Au/NaNbO{sub 3} due to blockage of some pores of sodium niobate by gold doping. The photocatalytic performance of gold-doped sodium niobate was studied by degradation of malachite green dye using visible light irradiation. The results demonstrate that the photocatalytic performance of gold-doped sodium niobate is higher than that of sodium niobate and TiO{sub 2} Degussa under visible light irradiation. - Highlights: • Au/NaNbO{sub 3} were used for photocatalytic degradation of malachite green dye. • Photocatalytic degradation was dependent on wt % of Au; reaction time, and weight of catalyst. • Catalyst re-use revealed the present photocatalyst remain effective and active after five cycles.

Electronic structure and lattice dynamics at the interface of single layer FeSe and SrTiO3

Science.gov (United States)

Ahmed, Towfiq; Balatsky, Alexander; Zhu, Jian-Xin

Recent discovery of high-temperature superconductivity with the superconducting energy gap opening at temperatures close to or above the liquid nitrogen boiling point in the single-layer FeSe grown on SrTiO3 has attracted significant interest. It suggests that the interface effects can be utilized to enhance the superconductivity. It has been shown recently that the coupling between the electrons in FeSe and vibrational modes at the interface play an important role. Here we report on a detailed study of electronic structure and lattice dynamics in the single-layer FeSe/SrTiO3 interface by using the state-of-art electronic structure method within the density functional theory. The nature of the vibrational modes at the interface and their coupling to the electronic degrees of freedom are analyzed. In addition, the effect of hole and electron doping in SrTiO3 on the electron-mode coupling strength is also considered. This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. DOE at LANL under Contract No. DE-AC52-06NA25396, and was supported by the DOE Office of Basic Energy Sciences.

DFT insights into the electronic and optical properties of fluorine-doped monoclinic niobium pentoxide (B-Nb{sub 2}O{sub 5}:F)

Energy Technology Data Exchange (ETDEWEB)

El-Shazly, Tamer S.; Rehim, Sayed S.A. [Ain-Shams University, Chemistry Department, Faculty of Science, Cairo (Egypt); Hassan, Walid M.I. [Cairo University, Chemistry Department, Faculty of Science, Giza (Egypt); Allam, Nageh K. [American University in Cairo, Energy Materials Lab (EML), School of Sciences and Engineering, New Cairo (Egypt)

2016-09-15

We report on the effect of fluorine doping on the electronic structure and optical properties of monoclinic niobium pentoxide (B-Nb{sub 2}O{sub 5}) as revealed by the first principles calculations. Density functional theory (DFT) along with generalized gradient approximation (GGA) at the revised Perdew-Burke-Ernzerhof (PBEsol) exchange-correlation functional was used in this study. The band calculations revealed that the studied materials are indirect bandgap semiconductors, with bandgap energies of 2.67 and 2.28 eV for the undoped and F-doped B-Nb{sub 2}O{sub 5}, respectively. Upon doping B-Nb{sub 2}O{sub 5}, the Fermi level shifts towards the conduction band, allowing optical absorption in the visible region with enhanced transmittance in the wavelength range 400-1000 nm. The calculated static refractive index of the undoped B-Nb{sub 2}O{sub 5} is in good agreement with the reported experimental value, which is enhanced upon F-incorporation resulting in cladding properties for the F-doped B-Nb{sub 2}O{sub 5}. Also, the effective mass of free charge carriers increased upon F-doping. The enhanced properties were attributed to the effect of the excessive valent electron of the incorporated F atom. (orig.)

Synthesis of Ag-loaded SrTiO_3/TiO_2 heterostructure nanotube arrays for enhanced photocatalytic performances

International Nuclear Information System (INIS)

Hu, Zijun; Chen, Da; Zhan, Xiaqiang; Wang, Fang; Qin, Laishun; Huang, Yuexiang

2017-01-01

In this work, the effect of loading Ag nanoparticles on the photocatalytic activity of SrTiO_3/TiO_2 nanotube arrays (TNTAs) was investigated. TNTAs were partially transformed to SrTiO_3 through a hydrothermal treatment, which could preserve the tubular structure of TNTAs, and then, Ag nanoparticles were well deposited on the surface of SrTiO_3/TNTAs heterostructure by a chemical reduction process. Compared to the TNTAs sample, the Ag-loaded SrTiO_3/TNTAs sample showed significantly enhanced photocatalytic activities for photodegradation of rhodamine B. The enhanced photocatalytic activity of Ag-loaded SrTiO_3/TNTAs could be attributed to the increased optical absorption as well as the efficient charge transfer and separation of photogenerated electron-hole pairs induced by the SrTiO_3/TNTAs heterojunction and the Schottky barrier between metallic Ag and SrTiO_3/TNTAs. On the basis of the trapping experiments, the possible photocatalytic mechanism was also discussed. (orig.)

EPR of photochromic Mo3+ in SrTiO3

NARCIS (Netherlands)

Kool, Th.W.

2010-01-01

In single crystals of SrTiO_3, a paramagnetic center, characterized by S = 3/2 and hyperfine interaction with an I = 5/2 nuclear spin has been observed in the temperature range 4.2K-77K by means of EPR. The impurity center is attributed to Mo3+. No additional line splitting in the EPR spectrum due

Low-Temperature Sintering Li3Mg1.8Ca0.2NbO6 Microwave Dielectric Ceramics with LMZBS Glass

Science.gov (United States)

Wang, Gang; Zhang, Huaiwu; Liu, Cheng; Su, Hua; Jia, Lijun; Li, Jie; Huang, Xin; Gan, Gongwen

2018-05-01

Li3Mg1.8Ca0.2NbO6 ceramics doped with Li2O-MgO-ZnO-B2O3-SiO2 glass (LMZBS) were prepared via a solid-state route. The LMZBS glass effectively reduced the sintering temperature of Li3Mg1.8Ca0.2NbO6 ceramics to 950°C. The effects of the LMZBS glass on the sintering behavior, microstructures and microwave dielectric properties of Li3Mg1.8Ca0.2NbO6 ceramics are discussed in detail. Among all the LMZBS doped Li3Mg1.8Ca0.2NbO6 ceramics, the sample with 1 wt.% of LMZBS glass sintered at 950°C for 4 h exhibited good dielectric properties: ɛ r = 16.7, Q × f = 31,000 GHz (9.92 GHz), τ f = - 1.3 ppm/°C. The Li3Mg1.8Ca0.2NbO6 ceramics possessed excellent chemical compatibility with Ag electrodes, and could be applied in low temperature co-fired ceramics (LTCC) applications.

Direct Observation of Room-Temperature Stable Magnetism in LaAlO3/SrTiO3 Heterostructures.

Science.gov (United States)

Yang, Ming; Ariando; Zhou, Jun; Asmara, Teguh Citra; Krüger, Peter; Yu, Xiao Jiang; Wang, Xiao; Sanchez-Hanke, Cecilia; Feng, Yuan Ping; Venkatesan, T; Rusydi, Andrivo

2018-03-21

Along with an unexpected conducting interface between nonmagnetic insulating perovskites LaAlO 3 and SrTiO 3 (LaAlO 3 /SrTiO 3 ), striking interfacial magnetisms have been observed in LaAlO 3 /SrTiO 3 heterostructures. Interestingly, the strength of the interfacial magnetic moment is found to be dependent on oxygen partial pressures during the growth process. This raises an important, fundamental question on the origin of these remarkable interfacial magnetic orderings. Here, we report a direct evidence of room-temperature stable magnetism in a LaAlO 3 /SrTiO 3 heterostructure prepared at high oxygen partial pressure by using element-specific soft X-ray magnetic circular dichroism at both Ti L 3,2 and O K edges. By combining X-ray absorption spectroscopy at both Ti L 3,2 and O K edges and first-principles calculations, we qualitatively ascribe that this strong magnetic ordering with dominant interfacial Ti 3+ character is due to the coexistence of LaAlO 3 surface oxygen vacancies and interfacial (Ti Al -Al Ti ) antisite defects. On the basis of this new understanding, we revisit the origin of the weak magnetism in LaAlO 3 /SrTiO 3 heterostructures prepared at low oxygen partial pressures. Our calculations show that LaAlO 3 surface oxygen vacancies are responsible for the weak magnetism at the interface. Our result provides direct evidence on the presence of room-temperature stable magnetism and a novel perspective to understand magnetic and electronic reconstructions at such strategic oxide interfaces.

Vacancy induced metallicity at the CaHfO3/SrTiO3 interface

KAUST Repository

Nazir, Safdar

2011-03-31

Density functional theory is used to study the electronic properties of the oxide heterointerfaceCaHfO3/SrTiO3. Structural relaxation is carried out with and without O vacancies. As compared to related interfaces, strongly reduced octahedral distortions are found. Stoichiometric interfaces between the wide band gap insulatorsCaHfO3 and SrTiO3 turn out to exhibit an insulating state. However, interface metallicity is introduced by O vacancies, in agreement with experiment. The reduced octahedral distortions and necessity of O deficiency indicate a less complicated mechanism for the creation of the interfacial electron gas.

Vacancy induced metallicity at the CaHfO3/SrTiO3 interface

KAUST Repository

Nazir, Safdar; Pulikkotil, J. J.; Schwingenschlö gl, Udo; Singh, Nirpendra

2011-01-01

Density functional theory is used to study the electronic properties of the oxide heterointerfaceCaHfO3/SrTiO3. Structural relaxation is carried out with and without O vacancies. As compared to related interfaces, strongly reduced octahedral distortions are found. Stoichiometric interfaces between the wide band gap insulatorsCaHfO3 and SrTiO3 turn out to exhibit an insulating state. However, interface metallicity is introduced by O vacancies, in agreement with experiment. The reduced octahedral distortions and necessity of O deficiency indicate a less complicated mechanism for the creation of the interfacial electron gas.

Effects of Nb impurity on orthorhombic PbZrO{sub 3} crystals

Energy Technology Data Exchange (ETDEWEB)

Rivera, Richard; Stashans, Arvids [Grupo de FisicoquImica de Materiales, Instituto de Quimica Aplicada, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)], E-mail: arvids@utpl.edu.ec

2008-10-15

A study of Nb doping in lead zirconate (PbZrO{sub 3}) has been carried out by using a quantum-chemical method developed for crystals and a periodic supercell model. One of the Zr atoms was replaced by an Nb atom in the supercell consisting of 80 atoms. The obtained geometry optimization for the defective region points to defect-outward atomic movements, which are accompanied by some reduction of atomic charges. It is observed that an extra electron imposed by the Nb impurity is transferred to the conduction band of the material and contributes to the n-type electrical conductivity, explaining indirectly some of the experimental observations.

Epitaxial growth of SrTiO3/YBa2Cu3O7 - x heterostructures by plasma-enhanced metalorganic chemical vapor deposition

Science.gov (United States)

Liang, S.; Chern, C. S.; Shi, Z. Q.; Lu, P.; Safari, A.; Lu, Y.; Kear, B. H.; Hou, S. Y.

1994-06-01

We report heteroepitaxial growth of SrTiO3 on YBa2Cu3O7-x/LaAlO3 substrates by plasma-enhanced metalorganic chemical vapor deposition. X-ray diffraction results indicated that SrTiO3 films were epitaxially grown on a (001) YBa2Cu3O7-x surface with [100] orientation perpendicular to the surface. The film composition, with Sr/Ti molar ratio in the range of 0.9 to 1.1, was determined by Rutherford backscattering spectrometry and energy dispersive spectroscopy. The thickness of the SrTiO3 films is 0.1-0.2 μm. The epitaxial growth was further evidenced by high-resolution transmission electron microscopy and selected area diffraction. Atomically abrupt SrTiO3/YBa2Cu3O7-x interface and epitaxial growth with [100]SrTiO3∥[001]YBa2Cu3O7-x were observed in this study. The superconducting transition temperature of the bottom YBa2Cu3O7-x layer, as measured by ac susceptometer, did not significantly degrade after the growth of overlayer SrTiO3. The capacitance-voltage measurements showed that the dielectric constant of the SrTiO3 films was as high as 315 at a signal frequency of 100 KHz. The leakage current density through the SrTiO3 films is about 1×10-6 A/cm2 at 2-V operation. Data analysis on the current-voltage characteristic indicated that the conduction process is related to bulk-limited Poole-Frenkel emission.

Temperature-dependent optical absorption of SrTiO3

International Nuclear Information System (INIS)

Kok, Dirk J.; Irmscher, Klaus; Naumann, Martin; Guguschev, Christo; Galazka, Zbigniew; Uecker, Reinhard

2015-01-01

The optical absorption edge and near infrared absorption of SrTiO 3 were measured at temperatures from 4 to 1703 K. The absorption edge decreases from 3.25 eV at 4 K to 1.8 eV at 1703 K and is extrapolated to approximately 1.2 eV at the melting point (2350 K). The transmission in the near IR decreases rapidly above 1400 K because of free carrier absorption and is about 50% of the room temperature value at 1673 K. The free carriers are generated by thermal excitation of electrons over the band gap and the formation of charged vacancies. The observed temperature-dependent infrared absorption can be well reproduced by a calculation based on simple models for the intrinsic free carrier concentration and the free carrier absorption coefficient. The measured red shift of the optical absorption edge and the rising free carrier absorption strongly narrow the spectral range of transmission and impede radiative heat transport through the crystal. These effects have to be considered in high temperature applications of SrTiO 3 -based devices, as the number of free carriers rises considerably, and in bulk crystal growth to avoid growth instabilities. Temperature dependent optical absorption edge of SrTiO 3 , measured, fitted, and extrapolated to the melting point. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Structural characteristics of Mg-doped (1-x)(K0.5Na0.5)NbO3-xLiSbO3 lead-free ceramics as revealed by Raman spectroscopy

International Nuclear Information System (INIS)

Zhu, W L; Meng, Y; Pezzotti, G; Zhu, J L; Wang, M S; Zhu, B; Zhu, X H; Zhu, J G; Xiao, D Q

2011-01-01

This paper presents a Raman spectroscopic study of compositional-change-induced structure variation and of the related mechanism of Mg doping in LiSbO 3 (LS)-modified (K 0.5 Na 0.5 )NbO 3 (KNN) ceramics. With increasing LS content from 0 to 0.06, a discontinuous shift towards higher wavenumbers was found for the band position of the A 1g (v 1 ) stretching mode of KNN, accompanied by a clearly nonlinear broadening of this band and a decrease in its intensity. Such morphological changes in the Raman spectrum result from two factors: (i) changes in polarizability/binding strength of the O-Nb-O vibration upon incorporation of Li ions in the KNN perovskitic structure and (ii) a polymorphic phase transition (PPT) from orthorhombic to tetragonal (O → T) phase at x > 0.04. Upon increasing the amount, w, of Mg dopant incorporated into the (1-x)KNN-xLS ceramic structure, the intensity of the Raman bands are enhanced, while the peak position and the full width at half maximum of the A 1g (v 1 ) mode was found to experience a clear dependence on both w and x. Raman characterization revealed that the mechanism of Mg doping is strongly correlated with the concentration of Li in the perovskite structure: Mg 2+ ions will preferentially replace Li + ions for low Mg doping while replace K/Na ions for higher doping of Mg. The PPT O → T was also found to be altered by the introduction of Mg and the critical value of LS concentration, x O-T , for incipient O → T transition in the KNN-xLS-wMT system was strongly dependent on Mg content, with x O→T being roughly equal to 0.04 + 2w, for the case of dilute Mg alloying. (paper)

Novel transparent conducting oxide: Anatase Ti1-xNb xO2

International Nuclear Information System (INIS)

Furubayashi, Yutaka; Hitosugi, Taro; Yamamoto, Yukio; Hirose, Yasushi; Kinoda, Go; Inaba, Kazuhisa; Shimada, Toshihiro; Hasegawa, Tetsuya

2006-01-01

Single-crystalline Ti 1-x Nb x O 2 (x = 0.2) films of 40 nm thickness were deposited on SrTiO 3 (100) substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction measurement confirmed epitaxial growth of anatase (001) film. The resistivity of Ti 1-x Nb x O 2 films with x ≥ 0.03 is 2-3 x 10 -4 Ω cm at room temperature. The carrier density of Ti 1-x Nb x O 2 , which is almost proportional to the Nb concentration, can be controlled in a range of 1 x 10 19 to 2 x 10 21 cm -3 . Optical measurements revealed that internal transmittance in the visible and near-infrared region for films with x = 0.03 was more than 97%. These results demonstrate that the presently developed anatase Ti 1-x Nb x O 2 is one of the promising candidates for the practical TCOs

Structural, dielectric and magnetic studies of Ba and Nb codoped BiFeO{sub 3} multiferroics

Energy Technology Data Exchange (ETDEWEB)

Jangra, Sandhaya, E-mail: sndh17@gmail.com; Sanghi, Sujata; Agarwal, Ashish; Kaswan, Kavita; Rangi, Manisha; Singh, Ompal [Department of Applied Physics, Guru Jambheshwar University of Science and Technology, Hisar, Haryana-125001 (India)

2016-05-23

Polycrystalline materials with composition Bi{sub 0.8}Ba{sub 0.2}Fe{sub 1-x}Nb{sub x}O{sub 3} (x= 0.07, 0.10) were prepared via solid state reaction method. Preliminary analysis of structure was performed by XRD technique and confirmed formation of single phase crystalline materials. Rietveld refinement reveled that these materials have rhombohedral phase with R3c space group. Dielectric constant increased with temperature and Nb concentration. Ba and Nb co-doping suppress the spiral spin structure and produce net magnetization.

Avoiding polar catastrophe in the growth of polarly orientated nickel perovskite thin films by reactive oxide molecular beam epitaxy

International Nuclear Information System (INIS)

Yang, H. F.; Liu, Z. T.; Fan, C. C.; Xiang, P.; Zhang, K. L.; Li, M. Y.; Liu, J. S.; Yao, Q.; Shen, D. W.

2016-01-01

By means of the state-of-the-art reactive oxide molecular beam epitaxy, we synthesized (001)- and (111)-orientated polar LaNiO 3 thin films. In order to avoid the interfacial reconstructions induced by polar catastrophe, screening metallic Nb-doped SrTiO 3 and iso-polarity LaAlO 3 substrates were chosen to achieve high-quality (001)-orientated films in a layer-by-layer growth mode. For largely polar (111)-orientated films, we showed that iso-polarity LaAlO 3 (111) substrate was more suitable than Nb-doped SrTiO 3 . In situ reflection high-energy electron diffraction, ex situ high-resolution X-ray diffraction, and atomic force microscopy were used to characterize these films. Our results show that special attentions need to be paid to grow high-quality oxide films with polar orientations, which can prompt the explorations of all-oxide electronics and artificial interfacial engineering to pursue intriguing emergent physics like proposed interfacial superconductivity and topological phases in LaNiO 3 based superlattices.

Ferroelectricity of strained SrTiO3 in lithium tetraborate glass-nanocomposite and glass-ceramic

Science.gov (United States)

Abdel-Khalek, E. K.; Mohamed, E. A.; Kashif, I.

2018-02-01

Glass-nanocomposite (GNCs) sample of the composition [90Li2B4O7-10SrTiO3] (mol %) was prepared by conventional melt quenching technique. The glassy phase and the amorphous nature of the GNCs sample were identified by Differential thermal analysis (DTA) and X-ray diffraction (XRD) studies, respectively. DTA of the GNCs exhibits sharp and broad exothermic peaks which represent the crystallization of Li2B4O7 and SrTiO3, respectively. The tetragonal Li2B4O7 and tetragonal SrTiO3 crystalline phases in glass-ceramic (GC) were identified by XRD and scanning electron microscopic (SEM). The strain tetragonal SrTiO3 phase in GNCs and GC has been confirmed by SEM. The values of crystallization activation energies (Ec1 and Ec2) for the first and second exothermic peaks are equal to 174 and 1452 kJ/mol, respectively. The Ti3+ ions in tetragonal distorted octahedral sites in GNCs were identified by optical transmission spectrum. GNCs and GC samples exhibit broad dielectric anomalies at 303 and 319 K because of strained SrTiO3 ferroelectric, respectively.

Crystalline phase, profile characteristics and spectroscopic properties of Er3+/Tm3+-diffusion-codoped LiNbO3 crystal

International Nuclear Information System (INIS)

Sun, Wen-Bao; Zhang, Zi-Bo; Sun, Hong-Xue; Wong, Wing-Han; Yu, Dao-Yin; Pun, Edwin Yue-Bun

2017-01-01

Er 3+ /Tm 3+ -codoped LiNbO 3 crystal was prepared by co-diffusion of stacked Er and Tm metal films coated onto surface of off-congruent, Li-deficient LiNbO 3 substrate produced by Li-poor vapor transport equilibration technique. The crystalline phase on the diffused surface was analyzed by X-ray single-crystal diffraction. The Er 3+ and Tm 3+ profile characteristics were studied by secondary ion mass spectrometry. The emission spectra were measured under the 980 or 795 nm wavelength excitation, and the emission and absorption cross section spectra were calculated based upon McCumber theory. The lifetimes of some emissions were measured. The results show that the Er 3+ and Tm 3+ ions presence is in the form of LiNbO 3 phase. Both ions obey to Gaussian profile with a diffusion depth 21.5 μm. In the codoping case, both ions keep their respective spectroscopic features of only doping case and do not affect each other. The codoping enables to combine the wavelength emissions of both ions and the resultant emission band in the telecommunication window around 1.5 μm is as wide as 150 nm, providing the possibility of S+C+L broadband amplification by employing commercial 980 and 795 nm laser diodes as the pump sources. The Er 3+ /Tm 3+ -codoped LN is a promising host material for integrated optics. - Graphical abstract: Er 3+ /Tm 3+ -codoped LiNbO 3 crystal was prepared by co-diffusion of stacked Er and Tm metal films. The crystalline phase, diffusion profile and cross section spectra of Er 3+ and Tm 3+ ions in the diffusion layer have been investigated. The results show that the presence of Er 3+ and Tm 3+ ions is in the LiNbO 3 phase. Both ions follow Gaussian profile with a diffusion depth 21.5 μm. Both ions keep their respective spectroscopic features of only doping case. Excited state absorption is the dominant process for 795-nm-upconvered fluorescence of Tm 3+ . The codoping enables to combine the wavelength emissions of both ions and provide the possibility of S

Strong composition dependence of resistive switching in Ba1-xSrxTiO3 thin films on semiconducting substrates and its thermodynamic analysis

OpenAIRE

Mohammad Moradi, Omid; Şen, Canhan; Sen, Canhan; Boni, A. G.; Pintilie, L.; Mısırlıoğlu, Burç; Misirlioglu, Burc

2018-01-01

In this work, we report on the variability of the Schottky effect in solution processed Ba1-xSrxTiO3 films (BST, x = 0, 0.5) grown on 0.5% Nb doped SrTiO3 substrates with top Pt electrodes (NSTO/BST/Pt). The films display leakage currents accompanied by varying degrees of hystereses in the current-voltage measurements. The magnitude of the leakage and hystereses depend on the Sr content. We focus on the current-voltage (I-V) behavior of our samples in the light of thermodynamic theory of ferr...

Carrier density independent scattering rate in SrTiO3-based electron liquids.

Science.gov (United States)

Mikheev, Evgeny; Raghavan, Santosh; Zhang, Jack Y; Marshall, Patrick B; Kajdos, Adam P; Balents, Leon; Stemmer, Susanne

2016-02-10

We examine the carrier density dependence of the scattering rate in two- and three-dimensional electron liquids in SrTiO3 in the regime where it scales with T(n) (T is the temperature and n ≤ 2) in the cases when it is varied by electrostatic control and chemical doping, respectively. It is shown that the scattering rate is independent of the carrier density. This is contrary to the expectations from Landau Fermi liquid theory, where the scattering rate scales inversely with the Fermi energy (EF). We discuss that the behavior is very similar to systems traditionally identified as non-Fermi liquids (n density-independent scattering rates have been observed. The results indicate that the applicability of Fermi liquid theory should be questioned for a much broader range of correlated materials and point to the need for a unified theory.

Thermal, defects, mechanical and spectral properties of Nd-doped GdNbO{sub 4} laser crystal

Energy Technology Data Exchange (ETDEWEB)

Ding, Shoujun [Chinese Academy of Sciences, Anhui Institute of Optics and Fine Mechanics, Hefei, Anhui Province (China); University of Science and Technology of China, Hefei (China); Zhang, Qingli; Luo, Jianqiao; Liu, Wenpeng; Wang, Xiaofei; Sun, Guihua; Li, Xiuli; Sun, Dunlu [Chinese Academy of Sciences, Anhui Institute of Optics and Fine Mechanics, Hefei, Anhui Province (China)

2017-05-15

A Nd-doped GdNbO{sub 4} crystal was grown successfully by Czochralski method. Its monoclinic structure was determined by X-ray diffraction; the unit-cell parameters are a = 5.38 Aa, b = 11.09 Aa, c = 5.11 Aa, and β = 94.56 . The morphological defects of Nd:GdNbO{sub 4} crystal were investigated using the chemical etching with the phosphoric acid etchant. For a new crystal, the physical properties are of great importance. The hardness and density of Nd:GdNbO{sub 4} were investigated first. Thermal properties of Nd:GdNbO{sub 4}, including thermal expansion coefficient and specific heat, were measured along a-, b-, and c-crystalline axes. Thermal properties indicate that the Nd:GdNbO{sub 4} pumped along c-axis can reduce the thermal lensing effect effectively. The specific heat is 0.53 J g{sup -1} K{sup -1} at 300 K, indicating a relatively high damage threshold of Nd:GdNbO{sub 4}. The transmission and emission spectrum of Nd:GdNbO{sub 4} were measured, and the absorption peaks were assigned. The strongest emission peak of Nd:GdNbO{sub 4} is located at 1065.3 nm in the spectral range of 850-1420 nm excited by 808 nm laser. The refractive index of Nd:GdNbO{sub 4} was calculated with the transmission spectrum and fitted with Sellmeier equation. All these obtained results is of great significance for the further research of Nd:GdNbO{sub 4}. (orig.)

Studies on advanced superconductors for fusion device. Pt. 1. Present status of Nb3Sn conductors

International Nuclear Information System (INIS)

Tachikawa, Kyoji; Yamamoto, Junya

1996-03-01

Nb 3 Sn conductors have been developed with great expectation as an advanced high-field superconductor to be used in fusion devices of next generation. Furthermore, Nb 3 Sn conductors are being developed for NMR magnet and superconducting generator as well as for cryogen-free superconducting magnet. A variety of fabrication procedures, such as bronze process, internal tin process and Nb tube method, have been developed based on the diffusion reaction. Recently, Nb 3 Sn conductors with ultra-thin filaments have been fabricated for AC use. Both high-field and AC performances of Nb 3 Sn conductors have been significantly improved by alloying addition. The Ti-doped Nb 3 Sn conductor has generated 21.5T at 1.8K operation. This report summarizes manufacturing procedures, superconducting performances and applications of Nb 3 Sn conductors fabricated through different processes in different countries. More detailed subjects included in this report are high-field properties, AC properties, conductors for fusion with large current capacities, stress-strain effect and irradiation effect as well as standardization of critical current measurement method regarding to Nb 3 Sn conductors. Comprehensive grasp on the present status of Nb 3 Sn conductors provided by this report will act as a useful data base for the future planning of fusion devices. (author). 172 refs

Effects of SrTiO3 on dielectric and piezoelectric properties of K0.48Na0.48Li0.04Nb0.96Ta0.04O3-based piezoceramics

International Nuclear Information System (INIS)

Bafandeh, Mohammad Reza; Abbasi, Mohammad Hasan; Saidi, Ali; Lee, Jae-Shin

2013-01-01

Highlights: ► Sodium potassium niobate based piezoceramics modified with SrTiO 3 (ST) were prepared. ► Crystal structure, microstructure and dielectric properties of ceramics were investigated. ► Addition of ST more than 3 mol% changed ferroelectric behavior from normal to relaxor. ► Coexistence of two structures in ceramic with 1 mol% ST enhanced piezoelectric constant. - Abstract: In this study, (100 − x) K 0.48 Na 0.48 Li 0.04 Nb 0.96 Ta 0.04 O 3 − xSrTiO 3 (0 ≤ x ≤ 10) ceramics were fabricated via normal sintering of synthesized powder by using solid state reaction. All ceramics revealed pure perovskite structure, indicating formation of solid solution between KNNLT and ST up to 10%. With increasing x, the crystal structure of ceramics changed from orthorhombic to tetragonal and finally pseudocubic symmetry when x = 10. Ceramic containing 1% ST had orthorhombic and tetragonal symmetries, simultaneously. Investigation of the variation of dielectric constant of ceramics versus temperature revealed that for ceramic with x = 1, polymorphic phase transition (PPT) temperature between orthorhombic and tetragonal is less than room temperature. Thus coexistence of two different structures in this ceramic is due to vicinity of its composition to morphotropic phase boundary (MPB). As a result, the maximum piezoelectric constant was measured for this ceramic. Ceramics containing 5 and 7.5% ST tend to appear relaxor ferroelectric behavior which is because of chemical inhomogeneities in both A- and B-sites of the ABO 3 perovskite structure.

Interface properties of SrTiO3-based heterostructures studied by spectroscopy and high-resolution microscopy

International Nuclear Information System (INIS)

Pfaff, Florian Georg

2017-01-01

Oxide heterostructures can exhibit a variety of unexpected electronic and magnetic phenomena at their interfaces. A prominent example is the interface in LaAlO 3 /SrTiO 3 heterostructures where a two-dimensional electron system (2DES) forms if the LaAlO 3 thickness equals or exceeds a critical thickness of four unit cells. Similar to LaAlO 3 /SrTiO 3 an interface 2DES above a critical overlayer thickness has been observed in γ-Al 2 O 3 /SrTiO 3 . However, the electron mobility as well as the sheet carrier density exceed those of LaAlO 3 /SrTiO 3 heterostructures by more than one order of magnitude. This thesis is concerned with the growth and the characterization of these two types of interface systems with the main focus on the analysis of the physical properties at the interface and the understanding of their leading mechanisms. In regard to the sample fabrication it is demonstrated in the present thesis that the hitherto established growth routine of LaAlO 3 /SrTiO 3 by pulsed laser deposition has to be altered and optimized for the growth of γ-Al 2 O 3 . It is shown that growth monitoring by analyzing reflection high energy electron diffraction (RHEED) intensity oscillations is hindered by the formation of surface wave resonances. In order to avoid this effect, a modified growth geometry has to be used whereby also in this heterostructure systems monitoring of the layer-by-layer growth of γ-Al 2 O 3 /SrTiO 3 heterostructures by electron diffraction can be achieved. A so-called electronic reconstruction is discussed as the possible driving mechanism for the 2DES formation in LaAlO 3 /SrTiO 3 . In this scenario, the built-up potential within the polar LaAlO 3 overlayer is compensated by a charge transfer from the sample surface to the top most layers of the non-polar SrTiO 3 substrate. Furthermore, the properties of these heterostructures strongly depend on the used growth conditions. In the present work, for instance, a significant increase in the charge

Study of fluorine doped (Nb,Ir)O_2 solid solution electro-catalyst powders for proton exchange membrane based oxygen evolution reaction

International Nuclear Information System (INIS)

Kadakia, Karan Sandeep; Jampani, Prashanth H.; Velikokhatnyi, Oleg I.; Datta, Moni Kanchan; Patel, Prasad; Chung, Sung Jae; Park, Sung Kyoo; Poston, James A.; Manivannan, Ayyakkannu; Kumta, Prashant N.

2016-01-01

Graphical abstract: High surface area (∼300 m"2/g) nanostructured powders of nominal composition (Nb_1_−_xIr_x)O_2 and (Nb_1_−_xIr_x)O_2:10F have been synthesized and tested as oxygen evolution electro-catalysts for PEM based water electrolysis using a simple two-step chemical synthesis procedure. Superior electrochemical activity was demonstrated by fluorine doped compositions of (Nb_1_−_xIr_x)O_2 with an optimal composition (Nb_0_._7_5Ir_0_._2_5)O_2:10F (x = 0.25) demonstrating on-par performance with commercial hydrated IrO_2 and nanostructured in-house chemically synthesized IrO_2. Using first principles calculations, the electronic structure modification resulting in ∼75 at.% reduction (experimentally observed) in noble metal content without loss in catalytic performance and stability has been established. - Highlights: • (Nb_1_−_xIr_x)O_2:10F nanopowder electrocatalysts have been wet chemically synthesized. • (Nb_0_._7_5Ir_0_._2_5)O_2:10F exhibits superior electrochemical activity than pure IrO_2. • Stability of the (Nb,Ir)O_2:10F nanomaterials is comparable to pure (Nb,Ir)O_2. • High surface area F doped (Nb,Ir)O_2 are promising OER anode electro-catalysts. - Abstract: High surface area (∼300 m"2/g) nanostructured powders of (Nb_1_−_xIr_x)O_2 and (Nb_1_−_xIr_x)O_2:10F (∼100 m"2/g) have been examined as promising oxygen evolution reaction (OER) electro-catalysts for proton exchange membrane (PEM) based water electrolysis. Nb_2O_5 and 10 wt.% F doped Nb_2O_5 powders were prepared by a low temperature sol-gel process which were then converted to solid solution (Nb,Ir)O_2 and 10 wt.% F doped (Nb,Ir)O_2 [(NbIr)O_2:10F] electro-catalysts by soaking in IrCl_4 followed by heat treatment in air. Electro-catalyst powders of optimal composition (Nb_0_._7_5Ir_0_._2_5)O_2:10F with ∼75 at.% reduction in noble metal content exhibited comparable OER activity to commercial hydrated IrO_2 and nanostructured in-house chemically synthesized IrO_2

A Humidity Sensor Based on Nb-doped Nanoporous TiO2 Thin Film

Directory of Open Access Journals (Sweden)

Mansoor Anbia

2011-11-01

Full Text Available The humidity sensing properties of the sensor fabricated from Nb-doped nanoporous TiO2 by screen-printing on the alumina substrate with Ag-Pd interdigital electrodes have been investigated. The nanoporous thin film has been prepared by sol-gel technique. The product has been characterized by X-ray diffraction and scanning electron microscopy to analyze the structure and its morphology. It is found that the impedance of this sensor changes more than four orders of magnitude in the relative humidity (RH range of 11–95 % at 25 °C. The response and recovery time of the sensor are about 19 and 25 s, respectively, during the RH variation from 11 to 95 %. The sensor shows high humidity sensitivity, rapid response and recovery, prominent stability, good repeatability and narrow hysteresis loop. These results indicate that Nb-doped nanoporous TiO2 thin films have a great potential for humidity sensing applications in room temperature operations.

An ultrasonic therapeutic transducers using lead-free Na0.5K0.5NbO3-CuNb2O6 ceramics

International Nuclear Information System (INIS)

Yang, Ming-Ru; Chu, Sheng-Yuan; Tsai, Cheng-Che

2010-01-01

Research highlights: → In this paper, CN was added to NKN ceramics to decrease the sintering temperature and to improve the density and piezoelectric characteristics. The influence of CuNb 2 O 6 (CN) content on the microstructure, electrical properties, temperature stability, and mechanical properties of the synthesized samples was investigated. Results show that the samples synthesized with CN-doped not only improved the density but also exhibited superior piezoelectric characteristic, temperature stability of resonance frequency (TCF), and elastic stiffness coefficient than those of pure NKN piezoelectric ceramics. → The bulk density (4.47 g/cm 3 ), k p (40%), k t (45%), Q m (1642), C 33 D (19.64 x 10 10 N/m 2 ), TCF (-0.011%/ o C) and TCC (0.135%/ o C) values for NKN-01CN ceramics obtained from experiments show excellent 'hard' piezoelectric properties. Furthermore, a lead-free NKN-01CN ultrasonic therapeutic transducer was successfully driven by a self-tuning circuit. - Abstract: In this work, we reports on the CuNb 2 O 6 (CN) modified lead-free Na 0.5 K 0.5 NbO 3 (NKN) based piezoelectric ceramics were synthesized by solid-state reaction methods and sintered at 1075 o C for 3 h. A secondary phase of K 4 CuNb 8 O 23 was found in the XRD pattern of NKN-based ceramics as the CN dopants is 1 mol%. Microstructural analyses of un-doped and CN-doped ceramics were performed in a scanning electron microscope. The influence of CN content on the microstructure, electrical properties, temperature stability, and mechanical properties of the synthesized ceramics was investigated. The results show that the synthesized ceramics with CN-doped not only had improved density but also exhibited superior piezoelectric characteristics, temperature stability of resonance frequency (TCF), and a better elastic stiffness coefficient than those of pure NKN piezoelectric ceramics. The bulk density (4.47 g/cm 3 ), k p (40%), k t (45%), Q m (1642), C 33 D (19.64 x 10 10 N/m 2 ), TCF (-0

Effects of Sr2+ doping on the electrical properties of (Bi0.5Na0.50.94Ba0.06TiO3 ceramics

Directory of Open Access Journals (Sweden)

Amrita Singh

2015-03-01

Full Text Available The influence of SrTiO3 addition on the microstructure and various electrical properties of (Bi0.5Na0.50.94Ba0.06TiO3 (BNTBT6 ceramics, fabricated by a conventional high temperature solid state reaction, was investigated. Analysis of X-ray diffraction patterns revealed the formation of phase pure materials with tetragonal unit cell structure, tetragonality parameter c/a in the interval from 0.9940 to 1.0063 and crystallite sizes ranging from 33–76 nm for addition of 0.2 to 1 wt.% of SrTiO3. SEM studies indicated that Sr2+ doping led to decrease in grain size and non-homogeneity of grain distribution for higher SrTiO3 amount (>0.6 wt.%. Complex impedance, modulus, and conductivity studies indicated the presence of grains and grain boundary contribution, non-Debye type of relaxation and NTCR behaviour of the test ceramic samples. Temperature dependent real part of complex permittivity showed peaks at 475 °C and the dielectric loss tangent showed peaks corresponding to 125 °C and 475 °C for almost all compositions. AC activation energies, computed using Arrhenius relation in the temperature range of 325–500 °C for the BNTBT6 ceramic compositions having SrTiO3 concentration from 0.2 to 1.0 wt.%, were seen to have maximal values at the lowest measurement frequency. Amongst the different chosen doped BNTBT6 ceramic compositions, the composition having 0.6 wt.% of SrTiO3 showed the best ferroelectric and piezoelectric response with maximum value of Pr (8.24 µC/cm2, minimum value of Ec (5.73 kV/mm and maximum d33 value (∼46 pC/N.

The creep of UO2 fuel doped with Nb2O5

International Nuclear Information System (INIS)

Sawbridge, P.T.; Reynolds, G.L.; Burton, B.

1981-01-01

The creep of UO 2 containing small additions of Nb 2 O 5 has been investigated in the stress range 0.5-90 MN/m 2 at temperatures between 1422 and 1573 K. The functional dependence of the creep rate of five dopant concentrations up to 0.8 mol% Nb 2 O 5 has been examined and it was established that in all the materials the secondary creep rate could be represented by the equation epsilonkT = Asigmasup(n) exp(-Q/RT), where epsilon is the steady state creep rate per hour, Q the activation energy and A and n are constants for each material. It was observed that Nb 2 O 5 additions can cause a dramatic increase in the steady state creep rate as long as the niobium ion is maintainde in the Nb 5+ valence state. Material containing 0.4 mol% Nb 2 O 5 creeps three orders of magnitude faster than the pure material. Analysis of the results in terms of grain size compensated viscosity suggest that, like pure UO 2 , the creep rate of Nb 2 O 5 doped fuel is diffusion-controlled and proportional to the reciprocal square of the grain size. A model is developed which suggests that the increase in creep rate results from suppression of the U 5+ ion concentration by the addition of Nb 5+ ions, which modifies the crystal defect structure and hence the uranium ion diffusion coefficient. (orig.)

Dielectric and Energy Storage Properties of Ba0.65Sr0.35TiO3 Ceramics Modified by BiNbO4

Science.gov (United States)

Zheng, Yi; Zhang, Jihua; Wei, Meng; Dong, Xiangxiang; Huang, Jiapeng; Wu, Kaituo; Chen, Hongwei

2018-02-01

(1 - x) (Ba0.65Sr0.35TiO3)-xBiNbO4 (x = 0.0-0.15) ceramic were prepared by solid-state reaction method. The phase composition, microstructure, dielectric properties, polarization-electric field, breakdown strength and energy storage behaviors for the BiNbO4-modified Ba0.65Sr0.35TiO3 ceramics were investigated. With the addition of BiNbO4, the remnant polarization and saturation polarization decreased and the nonlinearity was suppressed. When x = 0.07, the maximum recoverable energy storage achieved was 0.5 J/cm3, 1.5 times that of un-doped Ba0.65Sr0.35TiO3 ceramics, with an efficiency of 96.89% and a breakdown electric field reaching 15.3 kV/mm. Therefore, BiNbO4 doping could improve the energy storage properties of Ba0.65Sr0.35TiO3 for high-energy pulse capacitor application.

Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition

KAUST Repository

Yang, Yang

2014-11-01

Polarized Raman spectroscopy was used to study the lattice structure of BiFeO3 films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO3 films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50-700 cm-1 were identified based on group theory. The symmetries of the high order Raman modes in 900-1500 cm-1 of BiFeO3 are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400-700 cm-1 in return. Moreover, the lattice structures of BiFeO3 films are identified consequently on the basis of Raman spectroscopy. BiFeO3 films on SrRuO3 coated SrTiO3 (0 0 1) substrate, CaRuO3 coated SrTiO3 (0 0 1) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO3 film on SrRuO3 coated Nb: SrTiO3 (0 0 1) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO3 films.

Nanostructured TiO2 Doped with Nb as a Novel Support for PEMFC

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Edgar Valenzuela

2013-01-01

Full Text Available Nowadays, one of the major issues of the PEMFC concerns the durability. Historically, carbon has been used as a catalyst support in PEMFC; nevertheless, under the environmental conditions of the cell, the carbon is oxidized, leaving the catalyst unsupported. In order to increase the stability and durability of the catalyst in the PEMFC, a novel nanostructured metallic oxide support is proposed. In this work, TiO2 was doped with Nb to obtain a material that combines chemical stability, high surface area, and an adequate electronic conductivity in order to be a successful catalyst support candidate for long-term PEMFC applications. The TiO2-Nb nanostructured catalyst support was physically and electrochemically characterized. According to the results, the TiO2-Nb offers high surface area and good particle dispersion; also, the electrochemical activity and stability of the support were evaluated under high potential conditions, where the TiO2-Nb proved to be much more stable than carbon.

Nonvolatile resistive switching in Pt/laALO3/srTiO3 heterostructures

KAUST Repository

Wu, S.; Luo, X.; Turner, S.; Peng, H.; Lin, W.; Ding, J.; David, A.; Wang, B.; Van, Tendeloo, G.; Wang, J.; Wu, Tao

2013-01-01

Resistive switching heterojunctions, which are promising for nonvolatile memory applications, usually share a capacitorlike metal-oxide-metal configuration. Here, we report on the nonvolatile resistive switching in Pt/LaAlO3/SrTiO3 heterostructures

Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity.

Science.gov (United States)

Asmara, T C; Annadi, A; Santoso, I; Gogoi, P K; Kotlov, A; Omer, H M; Motapothula, M; Breese, M B H; Rübhausen, M; Venkatesan, T; Ariando; Rusydi, A

2014-04-14

In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e(-) from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥ 4 unit cells of LaAlO3) there is indeed a ~0.5e(-) transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤ 3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e(-) is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.

Electrical and microstructural properties of CaTiO3-doped K1/2Na1 ...

Indian Academy of Sciences (India)

KNN) and CaTiO3- modified K1/2Na1/2NbO3 (CTO-KNN) systems, were investigated. Discs doped with 0 to 0.55% mol of CaTiO3 (CTO) were sintered at 1125°C for 2 h. Although minority phases were found in doped samples, CaTiO3 was not ...

Epitaxial properties of ZnO thin films on SrTiO3 substrates grown by laser molecular beam epitaxy

International Nuclear Information System (INIS)

Wei, X. H.; Li, Y. R.; Zhu, J.; Huang, W.; Zhang, Y.; Luo, W. B.; Ji, H.

2007-01-01

Epitaxial ZnO thin films with different orientations have been grown by laser molecular beam epitaxy on (001)- (011)-, and (111)-orientated SrTiO 3 single-crystal substrates. The growth behavior was in situ monitored by reflection high-energy electron diffraction, and the epitaxial orientation relations were reconfirmed by ex situ x-ray diffraction measurements. In the case of ZnO on SrTiO 3 (001), four orthogonal domains coexisted in the ZnO epilayer, i.e., ZnO(110) parallel SrTiO 3 (001) and ZnO[-111] parallel SrTiO 3 . For (011)- and (111)-orientated substrates, single-domain epitaxy with c axial orientation was observed, in which the in-plane relationship was ZnO[110] parallel SrTiO 3 [110] irrespective of the substrate orientations. Additionally, the crystalline quality of ZnO on SrTiO 3 (111) was better than that of ZnO on SrTiO 3 (011) because of the same symmetry between the (111) substrates and (001) films. The obtained results can be attributed to the difference of the in-plane crystallographic symmetry. Furthermore, those alignments can be explained by the interface stress between the substrates and the films

Structural evolution of Ba8Ti3Nb4O24 from BaTiO3 using a series of Ba(Ti1−5xNb4x)O3 solid solutions

International Nuclear Information System (INIS)

Barrientos Hernández, F.R.; Lira Hernández, I.A.; Gómez Yáñez, C.; Arenas Flores, A.; Cabrera Sierra, R.; Pérez Labra, M.

2014-01-01

Highlights: • The evolution phase Ba 8 Ti 3 Nb 4 O 24 was obtained through the mechanism Ba(Ti 1-5x Nb 4x )O 3 . • Addition of niobium can accelerate grain growth of BaTiO 3 ceramics. • Ba 8 Ti 3 Nb 4 O 24 presents a dielectric loss of 0.0035 and permittivity value of 54.6. • Electrical measurements showed that Nb 5+ content drops Curie temperature. • Samples with x ⩾ 0.0625 shows an insulating behavior. -- Abstract: In this work, the structural evolution of hexagonal phase Ba 8 Ti 3 Nb 4 O 24 by adding Nb 2 O 5 to perovskite structure of BaTiO 3 was investigated. The compositions Ba(Ti 1-5x Nb 4x )O 3 ceramics, with 0.00025 ⩽ x ⩽ 0.125 were prepared by the conventional solid state route in air atmosphere, the powders precursors, BaTiO 3 , BaCO 3 and Nb 2 O 5 , were mixed in stoichiometric proportions and ground in a ball mill using alumina balls and acetone. The mixed powders were calcined at temperatures up to 1500 °C. The phase transformation of Ba 8 Ti 3 Nb 4 O 24 from BaTiO 3 was studied by DRX, Raman spectroscopy, SEM, electrical measurements (relative permittivity and P–E hysteresis loops); Rietveld’s refinement was used to structurally characterize the samples. For the devices obtained capacitance was measured at 1 kHz; with these values we calculated the relative permittivity. The samples show typical P–E hysteresis loops at room temperature accompanied by saturation polarization (Ps) and remnant polarization (Pr). The DRX and Rietveld’s refinement results show x ⩽ 0.01 has a ferroelectric behavior. When the doped level is increased x ⩾ 0.02, a peak displacement is observed, this is due to the phase transformation of tetragonal to cubic into the unit cell. Finally, with x = 0.125 the crystal structure transforms to the characteristic hexagonal phase Ba 8 Ti 3 Nb 4 O 24 which resonates at microwave frequencies

Optical decoherence and persistent spectral hole burning in Er3+:LiNbO3

International Nuclear Information System (INIS)

Thiel, C.W.; Macfarlane, R.M.; Boettger, T.; Sun, Y.; Cone, R.L.; Babbitt, W.R.

2010-01-01

Developing new resonant optical materials for spatial-spectral holography and quantum information applications requires detailed knowledge of the decoherence and population relaxation dynamics for the quantum states involved in the optical transitions, motivating the need for fundamental material studies. We report recent progress in studying these properties in erbium-doped lithium niobate at liquid helium temperatures. The influence of temperature, applied magnetic fields, measurement timescale, and dopant concentration were probed using photon echo spectroscopy and time-resolved spectral hole burning on the 1532 nm transition of Er 3+ :LiNbO 3 . Effects of spectral diffusion due to interactions between Er 3+ ions and between the Er 3+ ion and 7 Li and 93 Nb nuclear spins in the host lattice were observed. In addition, long-lived persistent spectral storage of seconds to minutes was observed due to non-equilibrium population redistribution among superhyperfine states.

Charge transfer mechanism for the formation of metallic states at the KTaO3/SrTiO3 interface

KAUST Repository

Nazir, Safdar

2011-03-29

The electronic and optical properties of the KTaO3/SrTiO3 heterointerface are analyzed by the full-potential linearized augmented plane-wave approach of density functional theory. Optimization of the atomic positions points at subordinate changes in the crystal structure and chemical bonding near the interface, which is due to a minimal lattice mismatch. The creation of metallic interface states thus is not affected by structural relaxation but can be explained by charge transfer between transition metal and oxygen atoms. It is to be expected that a charge transfer is likewise important for related interfaces such as LaAlO3/SrTiO3. The KTaO3/SrTiO3 system is ideal for disentangling the complex behavior of metallic interface states, since almost no structural relaxation takes place.

Promoting Photocatalytic Overall Water Splitting by Controlled Magnesium Incorporation in SrTiO3 Photocatalysts

NARCIS (Netherlands)

Han, Kai; Lin, Yen Chun; Yang, Chia Min; Jong, Ronald; Mul, Guido; Mei, Bastian

2017-01-01

SrTiO3 is a well-known photocatalyst inducing overall water splitting when exposed to UV irradiation of wavelengths <370 nm. However, the apparent quantum efficiency of SrTiO3 is typically low, even when functionalized with nanoparticles of Pt or Ni@NiO. Here, we introduce a simple solid-state

The effect of Nb doping on ferroelectric properties of PZT thin films prepared from polymeric precursors

International Nuclear Information System (INIS)

Souza, E.C.F.; Simoes, A.Z.; Cilense, M.; Longo, E.; Varela, J.A.

2004-01-01

Pure and Nb doped PbZr 0.4 Ti 0.6 O 3 thin films was prepared by the polymeric precursor method and deposited by spin coating on Pt/Ti/SiO 2 /Si (100) substrates and annealed at 700 deg. C. The films are oriented in (1 1 0) and (1 0 0) direction. The electric properties of PZT thin films show strong dependence of the crystallographic orientation. The P-E hysteresis loops for the thin film with composition PbZr 0.39 Ti 0.6 Nb 0.1 O 3 showed good saturation, with values for coercive field (E c ) equal to 60 KV cm -1 and for remanent polarization (P r ) equal to 20 μC cm -2 . The measured dielectric constant (ε) is 1084 for this film. These results show good potential for application in FERAM

Nb and Pd co-doped La0.57Sr0.38Co0.19Fe0.665Nb0.095Pd0.05O3-δ as a stable, high performance electrode for barrier-layer-free Y2O3-ZrO2 electrolyte of solid oxide fuel cells

Science.gov (United States)

Chen, Kongfa; He, Shuai; Li, Na; Cheng, Yi; Ai, Na; Chen, Minle; Rickard, William D. A.; Zhang, Teng; Jiang, San Ping

2018-02-01

La0.6Sr0.2Co0.2Fe0.8O3-δ (LSCF) is the most intensively investigated high performance cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs), but strontium segregation and migration at the electrode/electrolyte interface is a critical issue limiting the electrocatalytic activity and stability of LSCF based cathodes. Herein, we report a Nb and Pd co-doped LSCF (La0.57Sr0.38Co0.19Fe0.665Nb0.095Pd0.05O3-δ, LSCFNPd) perovskite as stable and active cathode on a barrier-layer-free anode-supported yttria-stabilized zirconia (YSZ) electrolyte cell using direct assembly method without pre-sintering at high temperatures. The cell exhibits a peak power density of 1.3 W cm-2 at 750 °C and excellent stability with no degradation during polarization at 500 mA cm-2 and 750 °C for 175 h. Microscopic and spectroscopic analysis show that the electrochemical polarization promotes the formation of electrode/electrolyte interface in operando and exsolution of Pd/PdO nanoparticles. The Nb doping in the B-site of LSCF significantly reduces the Sr surface segregation, enhancing the stability of the cathode, while the exsoluted Pd/PdO nanoparticles increases the electrocatalytic activity for the oxygen reduction reaction. The present study opens up a new route for the development of cobaltite-based perovskite cathodes with high activity and stability for barrier-layer-free YSZ electrolyte based IT-SOFCs.

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO thin films

Directory of Open Access Journals (Sweden)

Subodh K. Gautam

2015-12-01

Full Text Available The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1 mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.

Fe3Nb3N precipitates of the Fe3W3C type in Nb stabilized ferritic stainless steel

International Nuclear Information System (INIS)

Malfliet, A.; Van den Broek, W.; Chassagne, F.; Mithieux, J.-D.; Blanpain, B.; Wollants, P.

2011-01-01

Highlights: → The precipitation in Nb stabilized ferritic stainless steel at 950 deg. C is investigated. → We characterized the Fe 3 Nb 3 X precipitates with SAED, EELS, WDS and AES. → We found that Fe 3 Nb 3 X precipitates are stabilized by N and not by C or O. → This insight is new and important for future development of this type of steel grade. - Abstract: A Nb stabilized ferritic stainless steel with 0.45 wt.%Nb, 82 ppm C and 170 ppm N is investigated to reveal the nature of the precipitates present at 950 deg. C. In particular, Fe 3 Nb 3 X precipitates of the Fe 3 W 3 C type are analyzed with WDS and EELS to determine the light elements X stabilizing this phase in the steel. According to WDS on large precipitates after 500 h at 950 deg. C, the Fe 3 Nb 3 X phase contains 10.4 at.% N, 1.2 at.% O and 1.0 at.% C. Auger Electron Spectroscopy on the same precipitates confirms the presence of N. In addition, it is revealed that the C and O peaks observed with WDS result from surface contamination as they disappear after Ar sputtering. The presence of a N peak in the EELS spectra of small Fe 3 Nb 3 X precipitates which have formed after 6 min at 950 deg. C indicate that N stabilizes this phase already from the initial precipitation stage. With this analysis it is demonstrated that N is an effective stabilizer of Fe 3 Nb 3 X precipitates in ferritic stainless steels. The formation of this phase should therefore be considered when predicting the precipitation behavior of Nb in industrial Nb stabilized ferritic stainless steels containing residual N.

Voltage-controlled ferromagnetism and magnetoresistance in LaCoO3/SrTiO3 heterostructures

International Nuclear Information System (INIS)

Hu, Chengqing; Park, Keun Woo; Yu, Edward T.; Posadas, Agham; Demkov, Alexander A.; Jordan-Sweet, Jean L.

2013-01-01

A LaCoO 3 /SrTiO 3 heterostructure grown on Si (001) is shown to provide electrically switchable ferromagnetism, a large, electrically tunable magnetoresistance, and a vehicle for achieving and probing electrical control over ferromagnetic behavior at submicron dimensions. Fabrication of devices in a field-effect transistor geometry enables application of a gate bias voltage that modulates strain in the heterostructure via the converse piezoelectric effect in SrTiO 3 , leading to an artificial inverse magnetoelectric effect arising from the dependence of ferromagnetism in the LaCoO 3 layer on strain. Below the Curie temperature of the LaCoO 3 layer, this effect leads to modulation of resistance in LaCoO 3 as large as 100%, and magnetoresistance as high as 80%, both of which arise from carrier scattering at ferromagnetic-nonmagnetic interfaces in LaCoO 3 . Finite-element numerical modeling of electric field distributions is used to explain the dependence of carrier transport behavior on gate contact geometry, and a Valet-Fert transport model enables determination of spin polarization in the LaCoO 3 layer. Piezoresponse force microscopy is used to confirm the existence of piezoelectric response in SrTiO 3 grown on Si (001). It is also shown that this structure offers the possibility of achieving exclusive-NOR logic functionality within a single device

Strain Engineering of Ferroelectric Domains in KxNa1−xNbO3 Epitaxial Layers

Directory of Open Access Journals (Sweden)

Jutta Schwarzkopf

2017-08-01

Full Text Available The application of lattice strain through epitaxial growth of oxide films on lattice mismatched perovskite-like substrates strongly influences the structural properties of ferroelectric domains and their corresponding piezoelectric behavior. The formation of different ferroelectric phases can be understood by a strain-phase diagram, which is calculated within the framework of the Landau–Ginzburg–Devonshire theory. In this paper, we illustrate the opportunity of ferroelectric domain engineering in the KxNa1−xNbO3 lead-free material system. In particular, the following examples are discussed in detail: (i Different substrates (NdGaO3, SrTiO3, DyScO3, TbScO3, and GdScO3 are used to systematically tune the incorporated epitaxial strain from compressive to tensile. This can be exploited to adjust the NaNbO3 thin film surface orientation and, concomitantly, the vector of electrical polarization, which rotates from mainly vertical to exclusive in-plane orientation. (ii In ferroelectric NaNbO3, thin films grown on rare-earth scandate substrates, highly regular stripe domain patterns are observed. By using different film thicknesses, these can be tailored with regard to domain periodicity and vertical polarization component. (iii A featured potassium concentration of x = 0.9 of KxNa1−xNbO3 thin films grown on (110 NdScO3 substrates favors the coexistence of two equivalent, monoclinic, but differently oriented ferroelectric phases. A complicated herringbone domain pattern is experimentally observed which consists of alternating MC and a1a2 domains. The coexistence of different types of ferroelectric domains leads to polarization discontinuities at the domain walls, potentially enabling high piezoelectric responses. In each of these examples, the experimental results are in excellent agreement with predictions based on the linear elasticity theory.

Crystalline phase, profile characteristics and spectroscopic properties of Er{sup 3+}/Tm{sup 3+}-diffusion-codoped LiNbO{sub 3} crystal

Energy Technology Data Exchange (ETDEWEB)

Sun, Wen-Bao [Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072 (China); Key Laboratory of Optoelectronic Information Technology, Ministry of Education (Tianjin University), Tianjin 300072 (China); Zhang, Zi-Bo [Department of Engineering, Pierre and Marie Curie University (University of Paris VI), 4 place Jussieu, 75005 Paris (France); Sun, Hong-Xue [Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072 (China); Key Laboratory of Optoelectronic Information Technology, Ministry of Education (Tianjin University), Tianjin 300072 (China); Wong, Wing-Han, E-mail: eewhwong@cityu.edu.hk [Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072 (China); Key Laboratory of Optoelectronic Information Technology, Ministry of Education (Tianjin University), Tianjin 300072 (China); Department of Electronic Engineering and State Key Laboratory of Millimeter Waves, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong (China); Yu, Dao-Yin [Department of Opto-electronics and Information Engineering, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072 (China); Key Laboratory of Optoelectronic Information Technology, Ministry of Education (Tianjin University), Tianjin 300072 (China); Pun, Edwin Yue-Bun [Department of Electronic Engineering and State Key Laboratory of Millimeter Waves, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong (China); and others

2017-04-15

Er{sup 3+}/Tm{sup 3+}-codoped LiNbO{sub 3} crystal was prepared by co-diffusion of stacked Er and Tm metal films coated onto surface of off-congruent, Li-deficient LiNbO{sub 3} substrate produced by Li-poor vapor transport equilibration technique. The crystalline phase on the diffused surface was analyzed by X-ray single-crystal diffraction. The Er{sup 3+} and Tm{sup 3+} profile characteristics were studied by secondary ion mass spectrometry. The emission spectra were measured under the 980 or 795 nm wavelength excitation, and the emission and absorption cross section spectra were calculated based upon McCumber theory. The lifetimes of some emissions were measured. The results show that the Er{sup 3+} and Tm{sup 3+} ions presence is in the form of LiNbO{sub 3} phase. Both ions obey to Gaussian profile with a diffusion depth 21.5 μm. In the codoping case, both ions keep their respective spectroscopic features of only doping case and do not affect each other. The codoping enables to combine the wavelength emissions of both ions and the resultant emission band in the telecommunication window around 1.5 μm is as wide as 150 nm, providing the possibility of S+C+L broadband amplification by employing commercial 980 and 795 nm laser diodes as the pump sources. The Er{sup 3+}/Tm{sup 3+}-codoped LN is a promising host material for integrated optics. - Graphical abstract: Er{sup 3+}/Tm{sup 3+}-codoped LiNbO{sub 3} crystal was prepared by co-diffusion of stacked Er and Tm metal films. The crystalline phase, diffusion profile and cross section spectra of Er{sup 3+} and Tm{sup 3+} ions in the diffusion layer have been investigated. The results show that the presence of Er{sup 3+} and Tm{sup 3+} ions is in the LiNbO{sub 3} phase. Both ions follow Gaussian profile with a diffusion depth 21.5 μm. Both ions keep their respective spectroscopic features of only doping case. Excited state absorption is the dominant process for 795-nm-upconvered fluorescence of Tm{sup 3+}. The

Comparing Thermal Stability of NbTi and Nb$_3$Sn Wires

CERN Document Server

Breschi, M; Bottura, L; Devred, A; Trillaud, F

2009-01-01

The investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and Nb$_{3}$Sn wires in pool boiling Helium I. A comparison of the quench behavior of two typical NbTi and Nb$_{3}$Sn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and Nb$_{3}$Sn wires are reported and analyzed. It is shown that the Nb$_{3}$Sn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operation current and pulse duration and magnetic field. It is shown that the Nb$_{3}$Sn wire exhibits a ‘kink’ of the quench energy ...

Study of fluorine doped (Nb,Ir)O{sub 2} solid solution electro-catalyst powders for proton exchange membrane based oxygen evolution reaction

Energy Technology Data Exchange (ETDEWEB)

Kadakia, Karan Sandeep [Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Jampani, Prashanth H., E-mail: pjampani@pitt.edu [Bioengineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Velikokhatnyi, Oleg I.; Datta, Moni Kanchan [Bioengineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Center for Complex Engineered Multifunctional Materials, University of Pittsburgh, PA 15261 (United States); Patel, Prasad [Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Chung, Sung Jae [Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Park, Sung Kyoo [Bioengineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Poston, James A.; Manivannan, Ayyakkannu [US Department of Energy, National Energy Technology Laboratory, Morgantown, WV 26507 (United States); Kumta, Prashant N. [Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Bioengineering, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Center for Complex Engineered Multifunctional Materials, University of Pittsburgh, PA 15261 (United States); Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, PA 15261 (United States); Department of Oral Biology, School of Dental Medicine, University of Pittsburgh, PA 15217 (United States)

2016-10-15

Graphical abstract: High surface area (∼300 m{sup 2}/g) nanostructured powders of nominal composition (Nb{sub 1−x}Ir{sub x})O{sub 2} and (Nb{sub 1−x}Ir{sub x})O{sub 2}:10F have been synthesized and tested as oxygen evolution electro-catalysts for PEM based water electrolysis using a simple two-step chemical synthesis procedure. Superior electrochemical activity was demonstrated by fluorine doped compositions of (Nb{sub 1−x}Ir{sub x})O{sub 2} with an optimal composition (Nb{sub 0.75}Ir{sub 0.25})O{sub 2}:10F (x = 0.25) demonstrating on-par performance with commercial hydrated IrO{sub 2} and nanostructured in-house chemically synthesized IrO{sub 2}. Using first principles calculations, the electronic structure modification resulting in ∼75 at.% reduction (experimentally observed) in noble metal content without loss in catalytic performance and stability has been established. - Highlights: • (Nb{sub 1−x}Ir{sub x})O{sub 2}:10F nanopowder electrocatalysts have been wet chemically synthesized. • (Nb{sub 0.75}Ir{sub 0.25})O{sub 2}:10F exhibits superior electrochemical activity than pure IrO{sub 2}. • Stability of the (Nb,Ir)O{sub 2}:10F nanomaterials is comparable to pure (Nb,Ir)O{sub 2}. • High surface area F doped (Nb,Ir)O{sub 2} are promising OER anode electro-catalysts. - Abstract: High surface area (∼300 m{sup 2}/g) nanostructured powders of (Nb{sub 1−x}Ir{sub x})O{sub 2} and (Nb{sub 1−x}Ir{sub x})O{sub 2}:10F (∼100 m{sup 2}/g) have been examined as promising oxygen evolution reaction (OER) electro-catalysts for proton exchange membrane (PEM) based water electrolysis. Nb{sub 2}O{sub 5} and 10 wt.% F doped Nb{sub 2}O{sub 5} powders were prepared by a low temperature sol-gel process which were then converted to solid solution (Nb,Ir)O{sub 2} and 10 wt.% F doped (Nb,Ir)O{sub 2} [(NbIr)O{sub 2}:10F] electro-catalysts by soaking in IrCl{sub 4} followed by heat treatment in air. Electro-catalyst powders of optimal composition (Nb{sub 0.75}Ir

Unusual broadening of the NIR luminescence of Er{sup 3+}-doped Nb{sub 2}O{sub 5} nanocrystals embedded in silica host: Preparation and their structural and spectroscopic study for photonics applications

Energy Technology Data Exchange (ETDEWEB)

Aquino, Felipe Thomaz; Pereira, Rafael R. [Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, CEP 14040-901 Ribeirão Preto, SP (Brazil); Ferrari, Jefferson Luis [Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, CEP 14040-901 Ribeirão Preto, SP (Brazil); Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João Del Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, 36301-160 São João Del Rei, MG (Brazil); Ribeiro, Sidney José Lima [Laboratório de Materiais Fotônicos, Instituto de Química, UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Ferrier, Alban; Goldner, Philippe [Chimie-Paristech, Laboratoire de Chimie de la Matière Condensée de Paris, CNRS-UMR 7574, UPMC Univ Paris 06, 11 Rue Pierre et Marie Curie, 75005 Paris (France); and others

2014-10-15

This paper reports on the preparation of novel sol-gel erbium-doped SiO{sub 2}-based nanocomposites embedded with Nb{sub 2}O{sub 5} nanocrystals fabricated using a bottom-up method and describes their structural, morphological, and luminescence characterization. To prepare the glass ceramics, we synthesized xerogels containing Si/Nb molar ratios of 90:10 up to 50:50 at room temperature, followed by annealing at 900, 1000, or 1100 °C for 10 h. We identified crystallization accompanying host densification in all the nanocomposites with orthorhombic (T-phase) or monoclinic (M-phase) Nb{sub 2}O{sub 5} nanocrystals dispersed in the amorphous SiO{sub 2} phase, depending on the niobium content and annealing temperature. A high-intensity broadband emission in the near-infrared region assigned to the {sup 4}I{sub 13/2} → {sup 4}I{sub 15/2} transition of the Er{sup 3+} ions was registered for all the nanocomposites. The shape and the bandwidth changed with the Nb{sub 2}O{sub 5} crystalline phase, with values achieving up to 81 nm. Er{sup 3+} ions were located mainly in Nb{sub 2}O{sub 5}-rich regions, and the complex structure of the different Nb{sub 2}O{sub 5} polymorphs accounted for the broadening in the emission spectra. The materials containing the T-phase, displayed higher luminescence intensity, longer {sup 4}I{sub 13/2} lifetime and broader bandwidth. In conclusion, these nanostructured materials are potential candidates for photonic applications like optical amplifiers and WDM devices operating in the S, C, and L telecommunication bands. - Highlights: • Rare earth doped Nb{sub 2}O{sub 5} nanocrystals prepared from a bottom-up approach. • Unusual broadband NIR emission in glass ceramic system. • Structural features tuning the luminescence properties. • Potential as optical amplifiers and WDM devices. • Photonic devices operating in the S, C, and L telecommunication.

Comparison of the Thermal Degradation of Heavily Nb-Doped and Normal PZT Thin Films.

Science.gov (United States)

Yang, Jeong-Suong; Kang, YunSung; Kang, Inyoung; Lim, SeungMo; Shin, Seung-Joo; Lee, JungWon; Hur, Kang Heon

2017-03-01

The degradation of niobium-doped lead zirconate titanate (PZT) and two types of PZT thin films were investigated. Undoped PZT, two-step PZT, and heavily Nb-doped PZT (PNZT) around the morphotropic phase boundary were in situ deposited under optimum condition by RF-magnetron sputtering. All 2- [Formula: see text]-thick films had dense perovskite columnar grain structure and self-polarized (100) dominant orientation. PZT thin films were deposited on Pt/TiO x bottom electrode on Si wafer, and PNZT thin film was on Ir/TiW electrode with the help of orientation control. Sputtered PZT films formed on microelectromechanical system (MEMS) gyroscope and the degradation rates were compared at different temperatures. PNZT showed the best resistance to the thermal degradation, followed by two-step PZT. To clarify the effect of oxygen vacancies on the degradation of the film at high temperature, photoluminescence measurement was conducted, which confirmed that oxygen vacancy rate was the lowest in heavy PNZT. Nb-doping PZT thin films suppressed the oxygen deficit and made high imprint with self-polarization. This defect distribution and high internal field allowed PNZT thin film to make the piezoelectric sensors more stable and reliable at high temperature, such as reflow process of MEMS packaging.

Quenching effects on crystallographic and optical properties of H : LiNbO{sub 3} layers

Energy Technology Data Exchange (ETDEWEB)

Kalabin, I E [Institute of Semiconductor Physics, SB RAS, Lavrentiev Ave. 13, Novosibirsk, 630090 (Russian Federation); Shevtsov, D I [Perm Scientific-Industrial Instrument-Making Company, 25-October St. 106, Perm 614990 (Russian Federation); Azanova, I S [Perm Scientific-Industrial Instrument-Making Company, 25-October St. 106, Perm 614990 (Russian Federation); Taysin, I F [Perm Scientific-Industrial Instrument-Making Company, 25-October St. 106, Perm 614990 (Russian Federation); Atuchin, V V [Institute of Semiconductor Physics, SB RAS, Lavrentiev Ave. 13, Novosibirsk, 630090 (Russian Federation); Volyntsev, A B [Perm State University, 15 Bukireva St., Perm, 614990 (Russian Federation); Shilov, A N [Perm State University, 15 Bukireva St., Perm, 614990 (Russian Federation)

2004-07-07

The formation and decay of high temperature phases in H{sub x}Li{sub 1-x}NbO{sub 3} waveguide layers have been studied by means of waveguide mode spectroscopy and x-ray rocking curve measuring. The hydrogen doped layers with x {approx} 0.47 in (001) LiNbO{sub 3} were created by proton exchange reaction in melt benzoic acid. The high temperature phases were frozen by quenching from T 200 deg. C. It has been shown that these phases possess a 9% higher refractive index and 16% lower deformation in reference to the characteristic of H{sub x}Li{sub 1-x}NbO{sub 3} phase equilibrium at room conditions. The relaxation of the high temperature phase to the equilibrium one has been traced at T = 100 deg. C.

Site-specific doping, tunable dielectric properties and intrinsic ...

Indian Academy of Sciences (India)

Mn doping in SrTiO3 leads to the emergence of qualitatively distinct and novel physi- cal properties. We show that .... Mn K-edge XANES spectra of TiMn and SrMn, along with few reference compounds: SrMnO3 [20] ..... Mn3O4 nanoparticles,.

Prehistory effect on dielectric properties of NaNbO3-Gd1/3NbO3

International Nuclear Information System (INIS)

Burkhanov, A.I.; Bondarenko, P.V.; Shil'nikov, A.V.; Raevskaya, S.I.; Raevskij, I.P.

2006-01-01

One studied the low- and the infralow-frequency dielectric response of 0.9NaNbO 3 -0.1Gd 1/3 NbO 3 (NNG10) composition ceramics and single crystal at the material different prehistory. One revealed the differences in the nature of dielectric aging in NaNbO 3 antiferroelectric base material with a diffused phase transition in contrast to manifestation of similar phenomena in ferroelectrics-relaxors [ru

The role of the Mg sup 2 sup + ions in Cr sup 3 sup + spectroscopy for near-stoichiometric LiNbO sub 3 crystals

CERN Document Server

Han, T P J; Bermudez, V; Diéguez, E

2003-01-01

The optical spectroscopy of Cr sup 3 sup + ions doped into near-stoichiometric LiNbO sub 3 crystals, pure and co-doped with MgO, has been investigated. In the near-stoichiometric LiNbO sub 3 :Cr(0.2 mol%):Mg(2 mol%) crystal, the optical spectra resemble those previously observed for congruent LiNbO sub 3 :Cr:MgO samples when the total MgO content exceeds the 4.6 mol% threshold. The coexistence of two types of Cr sup 3 sup + centre ([Cr] sub L sub i and [Cr] sub N sub b) characterized the optical and luminescence spectra of this sample. The concentration equilibrium between the two types of centre is strongly displaced towards the [Cr sup 3 sup + ] sub N sub b centre, permitting us to obtain with accuracy the parameters of the broad bands. The R-line associated with the [Cr] sub N sub b centre is only observable in the low-temperature emission spectrum. The Fano anti-resonance lines present have been observed to be more pronounced for the near-stoichiometric samples than for congruent ones.

Effect of anode firing on the performance of lanthanum and nickel co-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3-δ) anode of solid oxide fuel cell

Science.gov (United States)

Park, Byung Hyun; Choi, Gyeong Man

2015-10-01

Perovskite oxides have potential for use as alternative anode materials in solid oxide fuel cells (SOFCs) due to stability in anode atmosphere; donor-doped SrTiO3 (e.g., La0.2Sr0.8TiO3-δ) is a good candidate for this purpose. Electro-catalytic nanoparticles can be produced in oxide anodes by the ex-solution method, e.g., by incorporating Ni into a perovskite oxide in air, then reducing the oxide in H2 atmosphere. In this study, we varied the temperature (1100, 1250 °C) and atmosphere (air, H2) of La0.2Sr0.8Ti0.9Ni0.1O3-δ (LSTN) anode firing to control the degree of Ni ex-solution and microstructure. LSTN fired at 1250 °C in H2 showed the best anodic performance for scandia-stabilized zirconia (ScSZ) electrolyte-supported cells in H2 and CH4 fuels due to the favorable microstructure and Ni ex-solution.

Temperature effect on the retention of U(VI) by SrTiO3

International Nuclear Information System (INIS)

Garcia Rosales, G.

2007-11-01

The purpose of this research was the study of the interaction mechanisms between U(VI) ions and SrTiO 3 surfaces versus pH and temperature: 25, 50, 75 and 90 C. Firstly, a physicochemical characterization was realized (DRX, MEB, FTIR) and the surface site density was determined. The potentiometric titration data were simulated, for each temperature, using the constant capacitance model and taking into account bath protonation of the ≡Sr-OH surface sites and deprotonation of the ≡Ti-OH ones (one pK a model). Both enthalpy and entropy changes, corresponding to the surface acid-base reactions, were evaluated using the van't Hoff relation. U(VI) was sorbed onto SrTiO 3 powder in the pH range 0.5-5.0 with an U(VI) initial concentration 1.10 -4 M. By TRLIFS two U(VI) complexes were detected associated with two lifetime values (60 ± 5 and 12 ± 2 μs at 25 C). The sorption edges were simulated using FITEQL 4.0 software. The surface complexation constants of the system SrTiO 3 /U(VI) between 25 and 90 C temperature range were thus obtained with the constant capacitance model considering two reactive surface sites. It reveals that two types of surface complex, namely [(≡SrOH)(≡TiOH)UO 2 ] 2+ and [(≡TiOH)(≡TiO)UO 2+ ] 2+ , are needed to properly describe the experimental observations. By application of the van't Hoff equation, Delta R S 0 and Delta R H 0 were obtained, which indicated an endothermic sorption process. Finally, an energy transfer study was realised by TRLIFS. The energy transfer between Tb 3+ and Eu 3+ ions sorbed onto SrTiO 3 powders were investigated. The results showed that the energy transfer between Tb 3+ and Eu 3+ is a non-radiative process and follows a dipole-dipole type interaction. A formalism based on the Dexter and the Inokuti-Hirayama theories was used to calculate the distances (2,7-3,4 Angstroms between Tb 3+ and Eu 3+ onto SrTiO 3 surface. (author)

Structural, electric and dielectric properties of Eu-doped SrBi2Nb2O9 ceramics obtained by co-precipitation route

Directory of Open Access Journals (Sweden)

Mohamed Afqir

2018-03-01

Full Text Available This paper presents a study of the structure and dielectric properties of Eu-doped SrBi2Nb2O9 ceramics prepared by co-precipitation route and sintered at 850 °C. The materials were examined using XRD and FTIR methods. XRD data indicated the formation of well crystallized structure of the pure and doped SrBi2Nb2O9, without the presence of undesirable phases. FTIR spectra do not bring a significant shift in the band positions. Moreover, the AC conductivity, dielectric constant and dielectric loss of the ceramics were determined through the frequency range [50 kHz–1 MHz]. In particular, the dielectric constant (ε′ and dielectric losses (tan δ of the SrBi2Nb2O9 and SrBi1.6Eu0.4Nb2O9 ceramics were measured as a function of temperature at various frequencies.

Electrical properties of niobium doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

International Nuclear Information System (INIS)

Parida, Geetanjali; Bera, J.

2013-01-01

Bismuth layer structured ferroelectrics (BLSFs) have attracted much attention because of their potential applications in non-volatile ferroelectric random access memories and high temperature piezoelectric. They are very attractive for these applications due to their fatigue free nature and environment friendly lead-free composition. BLSF crystal structure has layers of bismuth oxide and pseudo perovskite block stacked alternately along their c-direction, For commercial application, numerous efforts have been made to improve the electrical properties of BLSFs. Some effective approaches are: (i) doping at A-site, (ii) high valentcation doping at B-site and (iii) formation of intergrowth between different BLSFs. The intergrowth BLSFs are consist of regular stacking of one half the unit cell of m-member structure and one half the unit cell of (m+1) member BLSF structure along their c-axis. In this report, Nb-doped Bi 4 Ti 3 O 12 -SrBi 4 Ti 4 O 15 intergrowth ceramics have been prepared by modified oxalate route. XRD phase analysis confirmed the formation of single phase compound. Nb-doping does not affect the basic crystal structure of the intergrowth. SEM micrographs showed that the grain size of the ceramics decreases with Nb-doping. The temperature dependence of dielectric constant and losses was investigated in the temperature range 30 to 800℃ and frequency range 1 kHz to 1 MHz. With Nb-doping, the T c of the ferroelectrics reduces and peak permittivity increases. Doping also introduces small relaxor behaviour in the ferroelectrics. The dc conductivity of the ceramics decreases with doping. The remnant polarization (Pr) of the intergrowth ferroelectrics is increased with Nb doping. (author)

Liquidus projection of the Nb-Cr-Al system near the Al3(Nb,Cr) + Cr(Al,Nb) eutectic region

International Nuclear Information System (INIS)

Souza, S.A.; Ferrandini, P.L.; Nunes, C.A.; Coelho, A.A.; Caram, R.

2006-01-01

The system Nb-Cr-Al was investigated in the region near the Al 3 (Nb,Cr) + Cr(Al,Nb) eutectic and the liquidus projection of that region was determined based on the microstructural characterization of arc melted alloys. The characterization utilized scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and X-ray diffraction (XRD). The results allowed one to determine three primary solidification liquidus surfaces ((Cr,Al) 2 Nb, Cr(Al,Nb) and Al 3 (Nb,Cr)), that are originated from the binary systems Cr-Nb, Cr-Al and Al-Nb. It is proposed the occurrence of the invariant reaction L + (Cr,Al) 2 Nb ↔ Al 3 (Nb,Cr) + Cr(Al,Nb) and of a point of minimum, which involves a three phase reaction, L ↔ Al 3 (Nb,Cr) + Cr(Al,Nb). All alloys studied showed formation of the Al 3 (Nb,Cr) + Cr(Al,Nb) eutectic as the last solidification step with Al(Nb)Cr 2 precipitating from Cr(Al,Nb)

Continuous, flexible, and high-strength superconducting Nb3Ge and Nb3Sn filaments

International Nuclear Information System (INIS)

Ahmad, I.; Heffernan, W.J.

1976-01-01

Fabrication of continuous, flexible, and high-strength (1600 MN/m 2 ) composite filaments of Nb 3 Ge (T/subc/ 18 0 K) and Nb 3 Sn is reported, involving chemical vapor deposition of these compounds on Nb-coated high-strength W--1% ThO 2 filaments

Plasma plume effects on the conductivity of amorphous-LaAlO3/SrTiO3 interfaces grown by pulsed laser deposition in O2 and Ar

DEFF Research Database (Denmark)

Sambri, A.; Christensen, Dennis; Trier, Felix

2012-01-01

Amorphous-LaAlO3/SrTiO3 interfaces exhibit metallic conductivity similar to those found for the extensively studied crystalline-LaAlO3/SrTiO3 interfaces. Here, we investigate the conductivity of the amorphous-LaAlO3/SrTiO3 interfaces grown in different pressures of O2 and Ar background gases...

Surface interaction between cubic phase NaNbO3 nanoflowers and Ru nanoparticles for enhancing visible-light driven photosensitized photocatalysis

Science.gov (United States)

Chen, Wei; Hu, Yin; Ba, Mingwei

2018-03-01

Ru nanoparticles supported on perovskite NaNbO3 with cubic crystal structure and nanoflower-like morphology was prepared by a convenient solvothermal method combined with photo-deposition technique. Crystal structure, chemical component and surface valence states determined by XRD, XPS, TEM and SEM demonstrated the metastable cubic phase of perovskite NaNbO3, and its modified surface by Ru species. Optical and electrochemical analysis, such as UV-vis DRS, OTCS and EIS, indicated the excellent photoelectrochemical properties and the efficient electron transfer of the composites. Compared with naked and Ru-doped NaNbO3, the composite photocatalyst exhibited outstanding performance for the degradation of RhB under visible light irradiation due to the dye self-photosensitization and the surface interaction between Ru metal nanoparticles and semiconductor. In-situ reduction of surface Ru oxide species in the photocatalytic process assisted the further improvement of the photocatalytic activity and stability. Investigation of the main active species during the photocatalysis confirmed the efficient transfer of the photo-generated electrons and the positive effect of oxygen defects in NaNbO3. Finally, possible mechanism of the present visible-light driven photocatalysis was proposed in detail. This work provided an alternative strategy to enhance the visible-light photocatalytic efficiency of the catalyst with wide band gap on the basis of the synergistic effect of dye self-photosensitization, interaction between NaNbO3 and its surface Ru nanoparticles, and the "self-doping" of oxygen defects in NaNbO3.

Dielectric, ferroelectric and impedance spectroscopic studies of Mn and W modified AgNbO{sub 3} ceramics

Energy Technology Data Exchange (ETDEWEB)

Muduli, Rakesh; Kumar, Pawan, E-mail: pawankumar@nitrkl.ac.in; Panda, Ranjit Kumar; Panigrahi, Simanchal

2016-09-01

In the present study, the effect of heterovalent ion doping on the dielectric and ferroelectric behaviour of AgNbO{sub 3}/AN system was investigated. 0.04 mol of manganese (Mn{sup 4+}) and tungsten (W{sup 6+}) ions of smaller ionic radii were substituted in place of niobium (Nb{sup 5+}) ions in the AN system for generating hole and electron rich compounds, respectively. Better dielectric properties with improved saturation polarisations were observed in the heterovalent ions modified AN ceramics. The relaxation behaviour of the modified AN ceramics was investigated by impedance spectroscopy study and intrinsic grain conduction was found to be dominating in the chosen frequency and temperature ranges. The reduced resistivity of the modified AN ceramics was discussed in terms of calculated activation energy. The significant reduction of the activation energy was proposed as the possible cause of early arrival of relaxation peak in the electron doped AN system. - Highlights: • Holes and electrons doping effect on electrical properties of AN system. • Doping of holes significantly enhanced the ferroelectricity. • Doping of electrons reduced activation energy. • Reduced activation energy was related with grains relaxation process.

Native SrTiO3 (001) surface layer from resonant Ti L2,3 reflectance spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Valvidares, Manuel; Huijben, Mark; Yu, Pu; Ramesh, Ramamoorthy; Kortright, Jeffrey

2010-11-03

We quantitatively model resonant Ti L2,3 reflectivity Rs,p(q, hn) from several SrTiO3 (001) single crystals having different initial surface preparations and stored in ambient conditions before and between measurements. All samples exhibit unexpected 300 K Rs(hn) - Rp(hn) anisotropy corresponding to weak linear dichroism and tetragonal distortion of the TiO6 octahedra indicating a surface layer with properties different from cubic SrTiO3. Oscillations in Rs(q) confirm a ubiquitous surface layer 2-3 nm thick that evolves over a range of time scales. Resonant optical constant spectra derived from Rs,p(hn) assuming a uniform sample are refined using a single surface layer to fit measured Rs(q). Differences in surface layer and bulk optical properties indicate that the surface is significantly depleted in Sr and enriched in Ti and O. While consistent with the tendency of SrTiO3 surfaces toward non-stoichiometry, this layer does not conform simply to existing models for the near surface region and apparently forms via room temperature surface reactions with the ambient. This new quantitative spectral modeling approach is generally applicable and has potential to study near-surface properties of a variety of systems with unique chemical and electronic sensitivities.

Effect of Nb on plasticity and oxidation behavior of TiA1Nb intermetallic compound by density functional theory

Institute of Scientific and Technical Information of China (English)

LI Yan-feng; XU Hui; SONG Zhao-quan; MA Song-shan

2010-01-01

Based on the pseudo potential plane-wave method of density functional theory(DFT),Ti1-xNbxA1(x=0,0.062 5,0.083 3,0.125,0.250)crystals' geometry structure,elastic constants,electronic structure and Mulliken populations were calculated,and the effects of doping on the geometric structure,electronic structure and bond strength were systematically analyzed.The results show that the influence of Nb on the geometric structure is little in terms of the plasticity,and with the increase of Nb content,the covalent bond strength remarkably reduces,and Ti-A1,Nb-M(M=Ti,A1)and other hybrid bonds enhance; meanwhile,the peak district increases and the pseudo-energy gap first decreases and then increases,the overall band structure narrows,the covalent bond and direction of bonds reduce.The population analysis also shows that the results are consistent with the electronic structure analysis.The density of states of TiAlNb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film.All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5%(mole fraction).

An epitaxial transparent conducting perovskite oxide: double-doped SrTiO3

NARCIS (Netherlands)

Ravichandran, Jayakanth; Siemons, W.; Heijmerikx, Herman; Huijben, Mark; Majumdar, Arun; Ramesh, Ramamoorthy

2010-01-01

Epitaxial thin films of strontium titanate doped with different concentrations of lanthanum and oxygen vacancies were grown on LSAT substrates by pulsed laser deposition technique. Films grown with 5−15% La doping and a critical growth pressure of 1−10 mTorr showed high transparency (>70−95%) in the

Magnetization anomaly of Nb3Al strands and instability of Nb3Al Rutherford cables

International Nuclear Information System (INIS)

Yamada, Ryuji; Kikuchi, Akihiro; Wake, Masayoshi

2006-01-01

Using a Cu stabilized Nb 3 Al strand with Nb matrix, a 30 meter long Nb 3 Al Rutherford cable was made by a collaboration of Fermilab and NIMS. Recently the strand and cable were tested. In both cases instability was observed at around 1.5 Tesla. The magnetization of this Nb 3 Al strand was measured first using a balanced coil magnetometer at 4.2 K. Strands showed an anomalously large magnetization behavior around at 1.6 T, which is much higher than the usual B c2 ∼ 0.5 Tesla (4.2 K) of Nb matrix. This result is compared with the magnetization data of short strand samples using a SQUID magnetometer, in which a flux-jump signal was observed at 0.5 Tesla, but not at higher field. As a possible explanation for this magnetization anomaly, the interfilament coupling through the thin Nb films in the strands is suggested. The instability problem observed in low field tests of the Nb 3 Al Rutherford cables is attributed to this effect

Resistance switching at the interface of LaAlO3/SrTiO3

DEFF Research Database (Denmark)

Chen, Yunzhong; Zhao, J.L.; Sun, J.R.

2010-01-01

At the interface of LaAlO3/SrTiO3 with film thickness of 3 unit cells or greater, a reproducible electric-field-induced bipolar resistance switching of the interfacial conduction is observed on nanometer scale by a biased conducting atomic force microscopy under vacuum environment. The switching ...

Comparison Between Nb3Al and Nb3Sn Strands and Cables for High Field Accelerator Magnets

Energy Technology Data Exchange (ETDEWEB)

Yamada, R.; Kikuchi, A.; Barzi, E.; Chlachidze, G.; Rusy, A.; Takeuchi, T.; Tartaglia, M.; Turrioni, D.; Velev, V.; Wake, M.; Zlobin, A.V.; /Fermilab

2010-01-01

The Nb{sub 3}Al small racetrack magnet, SR07, has been successfully built and tested to its short sample limit beyond 10 Tesla without any training. Thus the practical application of Nb{sub 3}Al strands for high field accelerator magnets is established. The characteristics of the representative F4 strand and cable, are compared with the typical Nb{sub 3}Sn strand and cable. It is represented by the OST high current RRP Nb{sub 3}Sn strand with 108/127 configuration. The effects of Rutherford cabling to both type strands are explained and the inherent problem of the Nb{sub 3}Sn strand is discussed. Also the test results of two representative small racetrack magnets are compared from the stand point of Ic values, and training. The maximum current density of the Nb{sub 3}Al strands is still smaller than that of the Nb{sub 3}Sn strands, but if we take into account of the stress-strain characteristics, Nb{sub 3}Al strands become somewhat favorable in some applications.

Raman, dielectric and variable range hopping nature of Gd2O3-doped K0.5N0.5NbO3 piezoelectric ceramics

Directory of Open Access Journals (Sweden)

Mahesh Peddigari

2015-10-01

Full Text Available (K0.5Na0.5NbO3 (KNN + x wt% Gd2O3 (x = 0 -1.5 ceramics have been prepared by conventional solid state reaction method. The effect of Gd2O3 on the structural, microstructural and dielectric properties of KNN ceramics were studied systematically. The effect of Gd2O3 on phase transformation from orthorhombic to psuedocubic structure is explained interms of changes in the internal vibration modes of NbO6 octahedra. The Raman intensity of the stretching mode v1 enhanced and shifted toward higher wavenumber with Gd2O3 concentration, which is attributed to the increase in polarizability and change in the O-Nb-O bond angles. Microstructural analysis revealed that the grain size of the KNN ceramics decreases from 2.26 ± 1.07 μm to 0.35 ± 0.13 μm and becomes homogenous with an increase in Gd2O3 concentration. The frequency dependent dielectric spectra are analyzed by using Havriliak-Negami function. The fitted symmetry parameter and relaxation time (τ are found to be 0.914 and 8.78 × 10−10 ± 5.5 × 10−11 s, respectively for the sample doped with x = 1.0. The addition of Gd2O3 to the KNN shifted the polymorphic phase transition orthorhombic to tetragonal transition temperature (TO-T from 199oC to 85oC with enhanced dielectric permittivity (ε′ = 1139 at 1 MHz. The sample with x = 1.0, shown a high dielectric permittivity (ε′ = 879 and low dielectric loss (<5% in the broad temperature range (-140oC – 150oC with the Curie temperature 307 oC can have the potential for high temperature piezoelectric and tunable RF circuit applications. The temperature dependent AC-conductivity follows the variable range hopping conduction mechanism by obtaining the slope -0.25 from the ln[ln(ρac] versus ln(T graph in the temperature range of 133 K-308 K. The effect of Gd2O3 on the Mott’s parameters such as density of states (N(EF, hopping length (RH, and hopping energy (WH have been discussed.

Effect of Sr/Ti Ratio on the Photocatalytic Properties of SrTiO3

International Nuclear Information System (INIS)

Sulaeman, U; Yin, S; Sato, T

2011-01-01

Since strontium titanate is a wide gap semiconductor, it requires UV light to generate the photocatalytic activities. Modification of strontium titanate to show photocatalytic activity under visible light irradiation is the essential work to efficiently utilize the sun light energy for environmental application. It is expected that the synthesis of SrTiO 3 with variation of Sr/Ti atomic ratio could induce the defect crystals having unique photocatalytic properties. The SrTiO 3 with various Sr/Ti atomic ratios were synthesized by microwave-assisted solvothermal reaction of SrCl 2 .6H 2 O and Ti(OC 3 H 7 ) 4 in KOH aqueous solutions with different atomic ratios of Sr/Ti. The products were characterized by TG-DTA, XRD and DRS. The photocatalytic activity was determined by DeNO x ability using LED lamps with the wavelengths of 627 nm (red), 530 nm (green), 445 nm (blue) and 390 nm (UV). The nanoparticles of perovskite type SrTiO 3 with the particle size of 30-40 nm were successfully synthesized. The visible light responsive photocatalytic activity was generated by adding excess amount of Sr. The photocatalytic activity in visible light could be enhanced by an increase in the Sr/Ti atomic ratio up to 1.25, indicating that the visible light responsive photocatalytic activity is due to the generation of new band gap between the conduction band and valence band of SrTiO 3 by the formation of oxygen vacancy.

Releasing metal catalysts via phase transition: (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 as a redox stable anode material for solid oxide fuel cells.

Science.gov (United States)

Xiao, Guoliang; Wang, Siwei; Lin, Ye; Zhang, Yanxiang; An, Ke; Chen, Fanglin

2014-11-26

Donor-doped perovskite-type SrTiO3 experiences stoichiometric changes at high temperatures in different Po2 involving the formation of Sr or Ti-rich impurities. NiO is incorporated into the stoichiometric strontium titanate, SrTi0.8Nb0.2O3-δ (STN), to form an A-site deficient perovskite material, (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 (Ni-STN), for balancing the phase transition. Metallic Ni nanoparticles can be released upon reduction instead of forming undesired secondary phases. This material design introduces a simple catalytic modification method with good compositional control of the ceramic backbones, by which transport property and durability of solid oxide fuel cell anodes are largely determined. Using Ni-STN as anodes for solid oxide fuel cells, enhanced catalytic activity and remarkable stability in redox cycling have been achieved. Electrolyte-supported cells with the cell configuration of Ni-STN-SDC anode, La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode produce peak power densities of 612, 794, and 922 mW cm(-2) at 800, 850, and 900 °C, respectively, using H2 as the fuel and air as the oxidant. Minor degradation in fuel cell performance resulted from redox cycling can be recovered upon operating the fuel cells in H2. Such property makes Ni-STN a promising regenerative anode candidate for solid oxide fuel cells.

Optical decoherence and persistent spectral hole burning in Er{sup 3+}:LiNbO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Thiel, C.W., E-mail: thiel@physics.montana.ed [Spectrum Lab, Montana State University, Bozeman, MT 59717 (United States); Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Macfarlane, R.M. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); IBM Almaden Research Center, San Jose, CA 95120 (United States); Boettger, T. [Department of Physics, University of San Francisco, San Francisco, CA 94117 (United States); Sun, Y. [Department of Physics, University of South Dakota, Vermillion, SD 57069 (United States); Cone, R.L. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Babbitt, W.R. [Spectrum Lab, Montana State University, Bozeman, MT 59717 (United States); Department of Physics, Montana State University, Bozeman, MT 59717 (United States)

2010-09-15

Developing new resonant optical materials for spatial-spectral holography and quantum information applications requires detailed knowledge of the decoherence and population relaxation dynamics for the quantum states involved in the optical transitions, motivating the need for fundamental material studies. We report recent progress in studying these properties in erbium-doped lithium niobate at liquid helium temperatures. The influence of temperature, applied magnetic fields, measurement timescale, and dopant concentration were probed using photon echo spectroscopy and time-resolved spectral hole burning on the 1532 nm transition of Er{sup 3+}:LiNbO{sub 3}. Effects of spectral diffusion due to interactions between Er{sup 3+} ions and between the Er{sup 3+} ion and {sup 7}Li and {sup 93}Nb nuclear spins in the host lattice were observed. In addition, long-lived persistent spectral storage of seconds to minutes was observed due to non-equilibrium population redistribution among superhyperfine states.

Comparing the thermal stability of NbTi and Nb3Sn wires

International Nuclear Information System (INIS)

Breschi, M; Trevisani, L; Bottura, L; Devred, A; Trillaud, F

2009-01-01

The investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and Nb 3 Sn wires in pool boiling helium I. A comparison of the quench behavior of two typical NbTi and Nb 3 Sn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and Nb 3 Sn wires are reported and analyzed. It is shown that the Nb 3 Sn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared by considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operating current, pulse duration, and magnetic field. It is shown that the Nb 3 Sn wire exhibits a 'kink' of the quench energy versus current curve that makes the quench energy of Nb 3 Sn lower than that of NbTi at some intermediate current levels. Both the qualitative differences of the voltage traces and the different behaviors of quench energies and velocities are interpreted through a coupled electromagnetic-thermal model, with special emphasis on the detailed description of heat exchange with liquid helium.

Prediction of two-dimensional electron gas mediated magnetoelectric coupling at ferroelectric PbTiO3/SrTiO3 heterostructures

Science.gov (United States)

Wei, Lan-ying; Lian, Chao; Meng, Sheng

2017-05-01

First-principles calculations predict the emergence of magnetoelectric coupling mediated by two-dimensional electron gas (2DEG) at the ferroelectric PbTiO3/SrTiO3 heterostructure. Free electrons endowed by naturally existing oxygen vacancies in SrTiO3 are driven to the heterostructure interface under the polarizing field of ferroelectric PbTiO3 to form a 2DEG. The electrons are captured by interfacial Ti atoms, which surprisingly exhibits ferromagnetism even at room temperature with a small critical density of ˜15.5 μ C /cm2 . The ferroelectricity-controlled ferromagnetism mediated by interfacial 2DEG shows strong magnetoelectric coupling strength, enabling convenient control of magnetism by electric field and vice versa. The PbTiO3/SrTiO3 heterostructure is cheap, easily grown, and controllable, promising future applications in low-cost spintronics and information storage at ambient condition.

Influence of Ta and Ti Doping on the High Field Performance of (Nb, Ta, Ti)3Sn Multifilamentary Wires based on Osprey Bronze with High Tin Content

International Nuclear Information System (INIS)

Abaecherli, V; Uglietti, D; Lezza, P; Seeber, B; Fluekiger, R; Cantoni, M; Buffat, P-A

2006-01-01

Ta and Ti are the most widely used additions for technical Nb 3 Sn multifilamentary superconductors. These elements are known to influence grain growth, grain morphology and chemical composition in the A15 layer, hence the current carrying properties of the wires over a wide magnetic field range. So far only few studies tried to compare systematically Ta and Ti doped and undoped Nb 3 Sn wires in the frame of the same work, down to a nanometric scale. We present an investigation on several multifilamentary (Nb, Ta, Ti) 3 Sn bronze route wires, fabricated at a laboratory scale, with various amounts of additives. The wires consist of fine filaments embedded in a Cu-Sn or Cu-Sn-Ti Osprey bronze with > 15 wt.% Sn and an external Cu stabilization. Microstructural observations are compared with the results of J c and n values measured up to 21 T at 4.2 and 2.2 K, and for longitudinal strains up to 0.5%. Non-Cu J c values up to 300 Amm -2 and n values up to 50 at 17 T and 4.2 K show clearly that wires with Ti addition to the bronze have a better performance with respect to wires with Ti additions to the filaments

Spin-Orbit Interaction and Kondo Scattering at the PrAlO3/SrTiO3 Interface

Science.gov (United States)

Mozaffari, Shirin; Guchhait, Samaresh; Markert, John

We have investigated the effect of oxygen content, in the PO2 range of 6 ×10-6 - 1 ×10-3 torr, on the spin-orbit (SO) interaction at PrAlO3/SrTiO3 interface. The most-conducting 2-D-like PrAlO3 interfaces were not as conducting as comparable LaAlO3 samples, indicating either a steric or mixed-valent effect. The least-conducting, most oxygenated PrAlO3 interface exhibits hole conductivity, a departure from the typical electron-doped behavior. For 10-5 and 10-4 torr samples, high-temperature metallic behavior is accompanied by an upturn in resistivity at low temperatures, consistent with Kondo scattering theory; analysis gives a Kondo temperature 17 K. The magnetoresistance (MR) for the low PO2-grown samples was modeled with a positive part due to weak anti-localization (WAL) from a strong SO interaction, and a negative part due to the Kondo effect. The variation of MR suggests a strong SO interaction for the 10-5 torr sample with HSO = 1.25 T in both field orientations. The WAL effect is smaller for higher PO2-grown samples, where the high-field MR is dominated by the Kondo effect.

Thermal infrared and microwave absorbing properties of SrTiO3/SrFe12O19/polyaniline nanocomposites

International Nuclear Information System (INIS)

Hosseini, Seyed Hossein; Zamani, Parisa; Mousavi, S.Y.

2015-01-01

Graphical abstract: We have developed a new perspective of applications and properties of conducting polymers. The combination of absorption ability prepared nanocomposites in the present of PANI display a great potential in organization of shielding structures into thermal IR and microwave. Further investigations using other conducting polymers to demonstrate their capability for advance thermal IR and microwave shielding devices is under way. The application of these samples may improve the IR thermographic detection, catalysis, sensors, magnetic data storage, electromagnetic resonance wave absorption, photonic crystals, and microelectronic devices and military aspects. - Highlights: • The SrTiO 3 /SrFe 12 O 19 /PANI exhibited electric and electromagnetic properties. • The SrTiO 3 /SrFe 12 O 19 /PANI has shielding structures into thermal IR and microwave. • Increasing weight ratios and thicknesses will increase thermal IR ability. • Increasing weight ratios and thicknesses will increase microwave absorption ability. - Abstract: Polyaniline (PANI) as a unique polymer that also has electromagnetic absorption used as the substrate. In this research, SrTiO 3 was synthesized as IR absorbent and core and then SrFe 12 O 19 as microwave absorbent was prepared on SrTiO 3 via co-precipitation method as the first shell. As the next step, PANI was coated on SrTiO 3 /SrFe 12 O 19 nanoparticles via in situ polymerization by multi core–shell structures (SrTiO 3 /SrFe 12 O 19 /PANI). Nanometer size and structures of samples were measured by TEM, XRD and FTIR. Morphology of nanocomposite was showed by SEM images. The magnetic and electric properties were also performed by VSM and four probe techniques. Thermal infrared (IR) absorption and microwave reflection loss of nanocomposites were investigated at 10–40 μm and 8–12 GHz, IR and microwave frequencies, respectively. The results showed that the SrTiO 3 /SrFe 12 O 19 /PANI nanocomposites have good compatible

High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

KAUST Repository

Cossu, Fabrizio

2013-01-28

First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

KAUST Repository

Cossu, Fabrizio; Schwingenschlö gl, Udo; Singh, Nirpendra

2013-01-01

First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

Hierarchical nitrogen doped bismuth niobate architectures: Controllable synthesis and excellent photocatalytic activity

International Nuclear Information System (INIS)

Hou, Jungang; Cao, Rui; Wang, Zheng; Jiao, Shuqiang; Zhu, Hongmin

2012-01-01

Graphical abstract: Efficient visible-light-driven photocatalysts of peony-like nitrogen doped Bi 3 NbO 7 hierarchical architectures and silver-layered Bi 3 NbO 7−x Nx heterostructures were successfully synthesized in this discovery. Highlights: ► N-Bi 3 NbO 7 architectures were synthesized via two-step hydrothermal process. ► Electronic structure calculations indicated that N replaced O in samples. ► Growth mechanism is proposed for transformation of nanoparticles to microflowers. ► Excellent activities of N-Bi 3 NbO 7 architectures were obtained for degradation. ► Enhanced photocatalytic performance was observed for Ag/N-Bi 3 NbO 7 architectures. - Abstract: Nitrogen doped bismuth niobate (N-Bi 3 NbO 7 ) hierarchical architectures were synthesized via a facile two-step hydrothermal process. XRD patterns revealed that the defect fluorite-type crystal structure of Bi 3 NbO 7 remained intact upon nitrogen doping. Electron microscopy showed the N-Bi 3 NbO 7 architecture has a unique peony-like spherical superstructure composed of numerous nanosheets. UV–vis spectra indicated that nitrogen doping in the compound results in a red-shift of the absorption edge from 450 nm to 470 nm. XPS indicated that [Bi/Nb]-N bonds were formed by inducing nitrogen to replace a small amount of oxygen in Bi 3 NbO 7−x N x , which is explained by electronic structure calculations including energy band and density of states. Based on observations of architectures formation, a possible growth mechanism was proposed to explain the transformation of polyhedral-like nanoparticles to peony-like microflowers via an Ostwald riping mechanism followed by self-assembly. The N-Bi 3 NbO 7 architectures due to the large specific surface area and nitrogen doping exhibited higher photocatalytic activities in the decomposition of organic pollutant under visible-light irradiation than Bi 3 NbO 7 nanoparticles. Furthermore, an enhanced photocatalytic performance was also observed for Ag

Influence of different substrates on the ionic conduction in LiCoO{sub 2}/LiNbO{sub 3} thin-film bi-layers

Energy Technology Data Exchange (ETDEWEB)

Horopanitis, E.E.; Perentzis, G.; Papadimitriou, L. [Aristotle University of Thessaloniki, Department of Physics, Section of Solid State Physics, Thessaloniki (Greece)

2008-07-01

LiNbO{sub 3} thin films, deposited by e-gun evaporation, show lithium deficiency, which is cured by ''Li doping''. The ''Li doping'' of the films was achieved by preparing a structure of Li-Nb-O/Li/Li-Nb-O, which after annealing forms a homogenized LiNbO{sub 3} layer because of diffusion of Li in the two Li-Nb-O layers. The LiCoO{sub 2}/LiNbO{sub 3} bi-layers were prepared either on Stainless Steel/TiN or on Al{sub 2}O{sub 3}/Co/Pt substrates/ohmic-contacts by depositing first either the cathode LiCoO{sub 2} or the electrolyte LiNbO{sub 3}. The Nyquist plots of the AC impedance measurements of all structures showed that the interfaces prepared on Stainless-Steel/TiN consisted of two semicircles. The structures deposited on Al{sub 2}O{sub 3}/Co/Pt showed a third semicircle, which is probably due to the roughness of the substrate. It is important that the ionic properties of the bi-layers with the cathode material deposited first, a usual structure in a microbattery, are improved compared to the other structures. The quality of the LiNbO{sub 3} layer depends very much on the substrate. It can be evaluated from Arrhenius plots that the activation energy of this layer is considerably lower when the whole structure is deposited on Stainless Steel/TiN. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Tunability of resonance frequencies in a superconducting microwave resonator by using SrTiO sub 3 ferroelectric films

CERN Document Server

Sok, J; Lee, E H

1998-01-01

An applied dc voltage varies the dielectric constant of ferroelectric SrTiO sub 3 films. A tuning mechanism for superconducting microwave resonators was realized by using the variation in the dielectric constant of SrTiO sub 3 films. In order to estimate the values of the capacitance, C, and the loss tangent, tan delta, of SrTiO sub 3 ferroelectric capacitors, we used high-temperature superconducting microwave resonators which were composed of two ports, two poles, and dc bias circuits at the zero-field points. SrTiO sub 3 ferroelectric capacitors successfully controlled the resonant frequency of the resonator. Resonant frequencies of 3.98 GHz and 4.20 GHz were measured at bias voltages of 0 V and 50 V which correspond to capacitance values of 0.94 pF and 0.7pF, respectively. The values of the loss tangent, tan delta sub e sub f sub f , obtained in this measurements, were about 0.01.

LCAO calculations of SrTiO3 nanotubes

International Nuclear Information System (INIS)

Evarestov, Robert; Bandura, Andrei

2011-01-01

The large-scale first-principles simulation of the structure and stability of SrTiO 3 nanotubes is performed for the first time using the periodic PBE0 LCAO method. The initial structures of the nanotubes have been obtained by the rolling up of the stoichiometric SrTiO 3 slabs consisting of two or four alternating (001) SrO and TiO 2 atomic planes. Nanotubes (NTs) with chiralities (n,0) and (n,n) have been studied. Two different NTs were constructed for each chirality: (I) with SrO outer shell, and (II) with TiO 2 outer shell. Positions of all atoms have been optimized to obtain the most stable NT structure . In the majority of considered cases the inner or outer TiO 2 shells of NT undergo a considerable reconstruction due to shrinkage or stretching of interatomic distances in the initial cubic perovskite structure. There were found two types of surface reconstruction: (1) breaking of Ti-O bonds with creating of Ti = O titanyl groups in outer surface; (2) inner surface folding due to Ti-O-Ti bending. Based on strain energy calculations the largest stability was found for (n,0) NTs with TiO 2 outer shell.

Microscopic characterization of Fe nanoparticles formed on SrTiO3(001 and SrTiO3(110 surfaces

Directory of Open Access Journals (Sweden)

Miyoko Tanaka

2016-06-01

Full Text Available Fe nanoparticles grown on SrTiO3 (STO {001} and {110} surfaces at room temperature have been studied in ultrahigh vacuum by means of transmission electron microscopy and scanning tunnelling microscopy. It was shown that some Fe nanoparticles grow epitaxially. They exhibit a modified Wulff shape: nanoparticles on STO {001} surfaces have truncated pyramid shapes while those on STO {110} surfaces have hexagonal shapes. From profile-view TEM images, approximate values of the adhesion energy of the nanoparticles for both shapes are obtained.

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.

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.

(Nd0⋅065Ti0⋅87Nb0⋅065)O3 ceramic

Indian Academy of Sciences (India)

Unknown

Polycrystalline ceramic samples of sodium bismuth titanate with simultaneous doping at A and B sites have been studied for the influence of ... of Nd and Nb at B site in BaTiO3 (BaNdxTi1–2xNbxO3). (Mahboob et al 2005a). Dielectric ..... hence the conduction arises due to short range translation hopping via large polarons.

Effect of thickness on optoelectrical properties of Nb-doped indium tin oxide thin films deposited by RF magnetron sputtering

Science.gov (United States)

Li, Shi-na; Ma, Rui-xin; Ma, Chun-hong; Li, Dong-ran; Xiao, Yu-qin; He, Liang-wei; Zhu, Hong-min

2013-05-01

Niobium-doped indium tin oxide (ITO:Nb) thin films are prepared on glass substrates with various film thicknesses by radio frequency (RF) magnetron sputtering from one piece of ceramic target material. The effects of thickness (60-360 nm) on the structural, electrical and optical properties of ITO: Nb films are investigated by means of X-ray diffraction (XRD), ultraviolet (UV)-visible spectroscopy, and electrical measurements. XRD patterns show the highly oriented (400) direction. The lowest resistivity of the films without any heat treatment is 3.1×10-4Ω·cm-1, and the resistivity decreases with the increase of substrate temperature. The highest Hall mobility and carrier concentration are 17.6 N·S and 1.36×1021 cm-3, respectively. Band gap energy of the films depends on substrate temperature, which varies from 3.48 eV to 3.62 eV.

Dehydration of Glucose to 5-Hydroxymethylfurfural Using Nb-doped Tungstite

KAUST Repository

Yue, Chaochao; Li, Guanna; Pidko, Evgeny A.; Wiesfeld, Jan J.; Rigutto, Marcello; Hensen, Emiel J. M.

2016-01-01

Dehydration of glucose to 5-hydroxymethylfurfural (HMF) remains a significant problem in the context of the valorization of lignocellulosic biomass. Hydrolysis of WCl6 and NbCl5 leads to precipitation of Nb-containing tungstite (WO3H2O) at low Nb

Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures

Science.gov (United States)

Groenendijk, D. J.; Manca, N.; Mattoni, G.; Kootstra, L.; Gariglio, S.; Huang, Y.; van Heumen, E.; Caviglia, A. D.

2016-07-01

Obtaining high-quality thin films of 5d transition metal oxides is essential to explore the exotic semimetallic and topological phases predicted to arise from the combination of strong electron correlations and spin-orbit coupling. Here, we show that the transport properties of SrIrO3 thin films, grown by pulsed laser deposition, can be optimized by considering the effect of laser-induced modification of the SrIrO3 target surface. We further demonstrate that bare SrIrO3 thin films are subject to degradation in air and are highly sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited in-situ is effective in preserving the film quality, allowing us to measure metallic transport behavior in films with thicknesses down to 4 unit cells. In addition, the SrTiO3 encapsulation enables the fabrication of devices such as Hall bars without altering the film properties, allowing precise (magneto)transport measurements on micro- and nanoscale devices.

Purely hopping conduction in c-axis oriented LiNbO3 thin films

Science.gov (United States)

Shandilya, Swati; Tomar, Monika; Sreenivas, K.; Gupta, Vinay

2009-05-01

Dielectric constant and ac conductivity of highly c-axis oriented LiNbO3 thin film grown by pulsed laser deposition were studied in a metal-insulator-metal configuration over a wide temperature (200 to 450 K) and frequency (100 Hz to 1 MHz) range. The preferred oriented Al (1%) doped ZnO film with electrical conductivity 1.1×103 Ω-1 cm-1 was deposited for dual purpose: (1) to serve as nucleating center for LiNbO3 crystallites along preferred c-axis growth direction, and (2) to act as a suitable bottom electrode for electrical studies. The room temperature dc conductivity (σdc) of LiNbO3 film was about 5.34×10-10 Ω-1 cm-1 with activation energy ˜0.3 eV, indicating extrinsic conduction. The ac conductivity σac was found to be much higher in comparison to σdc in the low temperature region (300 K), σac shows a weak frequency dependence, whereas dielectric constant exhibits a strong frequency dispersion. The dielectric dispersion data has been discussed in the light of theoretical models based on Debye type mixed conduction and purely hopping conduction. The dominant conduction in c-axis oriented LiNbO3 thin film is attributed to the purely hopping where both σdc and σac arise due to same mechanism.