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Sample records for nb doped srtio3

  1. Electrical transport across Au/Nb : SrTiO3 Schottky interface with different Nb doping

    NARCIS (Netherlands)

    Rana, K. G.; Khikhlovskyi, V.; Banerjee, T.

    2012-01-01

    We have investigated electron transport in Nb doped SrTiO3 single crystals for two doping densities. We find that the resistivity and mobility are temperature dependent in both whereas the carrier concentration is almost temperature invariant. We rationalize this using the hydrogenic theory for shal

  2. Enhanced carrier density in Nb-doped SrTiO3 thermoelectrics

    KAUST Repository

    Ozdogan, K.

    2012-03-08

    We study epitaxial SrTiO3 interfaced with Nb-doped SrTi1-x Nb x O3 (x = 0, 0.125, 0.25, 0.375, and 0.5) by full-potential density functional theory. From the electronic band structures obtained by our ab-initio calculations we determine the dependence of the induced metallicity on the Nb concentration. We obtain a monotonous increase of the carrier density with the Nb concentration. The results are confirmed by experiments for SrTi0.88Nb0.12O3 and SrTi0.8Nb0.2O3, demonstrating the predictive power and limitations of our theoretical approach. We also show that the Seebeck coefficient decreases monotonously with increasing temperature.

  3. Electrochemical characterization and redox behavior of Nb-doped SrTiO3

    DEFF Research Database (Denmark)

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

    2009-01-01

    Sr-vacancy compensated Nb-doped SrTiO3 with the nominal composition Sr0.94Ti0.9Nb0.1O3 has been evaluated as a solid oxide fuel cell (SOFC) anode material in terms of redox stability and electrochemical properties. Sr0.94Ti0.9Nb0.1O3 has been synthesized with a recently developed modified glycine......-nitrate process. The phase purity and redox behavior have been analyzed with XRD and TGA. The electrochemical properties of Sr0.94Ti0.9Nb0.1O3 and a composite electrode of Sr0.94Ti0.9Nb0.1O3/YSZ have been investigated by electrochemical impedance spectroscopy (EIS) on cone shaped electrodes and on electrodes...... in a symmetrical cell configuration. The experiments indicated that the Nb-doped SrTiO3 electrodes were redox stable and showed a potential ability to be used as a part of a SOFC anode. The electrochemical activity appeared to be governed by the concentration of defect species (especially Ti3+ and V-0...

  4. Defect and electrical transport properties of Nb-doped SrTiO3

    DEFF Research Database (Denmark)

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

    2008-01-01

    This study reports the defect and electrical transport properties of Nb-doped SrTiO3, Samples with various A/B-ratios were synthesized by a modified glycine-nitrate combustion process and evaluated as a constituent in a SOFC anode. The phase purity and defect structure of the materials have been......% H-2/N-2). The results were in agreement with the defect chemistry model of donor-doped SrTiO3 where the charge compensation changes from Sr vacancy compensation to the electronic type when samples are sintered in reducing atmosphere. XANES in combination with TGA indicated that Ti is the only...... species that is reduced to a lower oxidation state (from Ti4+ to Ti3+). The pre-edge fine structure (PEFS) from the XANES results indicated that Nb improved the overlap of the Ti atomic orbitals and thereby provided one more explanation for the positive effect of Nb on the electronic conductivity of Nb...

  5. Electronic structures and optical properties of Nb-doped SrTiO3 from first principles

    Science.gov (United States)

    Shujuan, Jiao; Jinliang, Yan; Guipeng, Sun; Yinnü, Zhao

    2016-07-01

    The n-type Nb-doped SrTiO3 with different doping concentrations were studied by first principles calculations. The effects of Nb concentration on the formation enthalpy, electronic structure and optical property were investigated. Results show that Nb preferentially enters the Ti site in SrTiO3, which is in good agreement with the experimental observation. The Fermi level of Nb-doped SrTiO3 moves into the bottom of the conduction band, and the system becomes an n-type semiconductor. The effect of Nb-doping concentration on the conductivity was discussed from the microscopic point of view. Furthermore, the 1.11 at% Nb-doped SrTiO3 shows strong absorption in the visible light and becomes a very useful material for photo-catalytic activity. The 1.67 at% and 2.5 at% Nb-doped models will be potential transparent conductive materials. Project supported by the National Natural Science Foundation of China (No. 10974077) and the Innovation Project of Shandong Graduate Education, China (No. SDYY13093).

  6. Performance-Microstructure Relations in Ni/CGO Infiltrated Nb-doped SrTiO3 SOFC Anodes

    DEFF Research Database (Denmark)

    Ramos, Tania; Bernuy-Lopez, Carlos; Reddy Sudireddy, Bhaskar;

    2012-01-01

    Nb-doped SrTiO3 solid oxide fuel cell (SOFC) anodes, infiltrated with CGO/Ni, were investigated by electrochemical impedance spectroscopy (EIS) and high resolution microscopy techniques, upon varying production and testing parameters. The electrochemical analysis involved a combination...

  7. Improved Thermoelectric Performances of SrTiO3 Ceramic Doped with Nb by Surface Modification of Nanosized Titania.

    Science.gov (United States)

    Li, Enzhu; Wang, Ning; He, Hongcai; Chen, Haijun

    2016-12-01

    Nb-doped SrTiO3 ceramics doped with the surface modification of nanosized titania was prepared via liquid phase deposition approach and subsequent sintered in an Ar atmosphere. The surface modification of nanosized titania significantly improved the ratio of the electrical conductivity to thermal conductivity of SrTiO3 ceramic doped with Nb, and has little impact on the Seebeck coefficient, thus obviously improving the dimensionless thermoelectric figure of merit (ZT value). The surface modification of nanosized titania is a much better method to lower the thermal conductivity and to enhance the electrical conductivity than the mechanical mixing process of nanosized titania. The highest ZT value of 0.33 at 900 K was obtained. The reason for the improved thermoelectric performances by the surface modification of nano-sized titania was preliminary investigated.

  8. Reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals

    Science.gov (United States)

    Liu, Z. Q.; Lü, W. M.; Lim, S. L.; Qiu, X. P.; Bao, N. N.; Motapothula, M.; Yi, J. B.; Yang, M.; Dhar, S.; Venkatesan, T.; Ariando

    2013-06-01

    The search for oxide-based room-temperature ferromagnetism has been one of the holy grails in condensed matter physics. Room-temperature ferromagnetism observed in Nb-doped SrTiO3 single crystals is reported in this Rapid Communication. The ferromagnetism can be eliminated by air annealing (making the samples predominantly diamagnetic) and can be recovered by subsequent vacuum annealing. The temperature dependence of magnetic moment resembles the temperature dependence of carrier density, indicating that the magnetism is closely related to the free carriers. Our results suggest that the ferromagnetism is induced by oxygen vacancies. In addition, hysteretic magnetoresistance was observed for magnetic field parallel to the current, indicating that the magnetic moments are in the plane of the samples. The x-ray photoemission spectroscopy, the static time-of-flight and the dynamic secondary ion mass spectroscopy and proton induced x-ray emission measurements were performed to examine the magnetic impurities, showing that the observed ferromagnetism is unlikely due to any magnetic contaminant.

  9. Major enhancement of the thermoelectric performance in Pr/Nb-doped SrTiO3 under strain

    KAUST Repository

    Amin, B.

    2013-07-16

    The electronic structure and thermoelectric properties of strained (biaxially and uniaxially) Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3 are investigated in the temperature range from 300 K to 1200 K. Substitutions of Pr at the Sr site and Nb at the Ti site generate n-type doping and thus improve the thermoelectric performance as compared to pristine SrTiO3. Further enhancement is achieved by the application of strain, for example, of the Seebeck coefficient by 21% for Sr0.95Pr0.05TiO3 and 10% for SrTi0.95Nb0.05O3 at room temperature in the case of 5% biaxial strain. At 1200 K, we predict figures of merit of 0.58 and 0.55 for 2.5% biaxially strained Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3 , respectively, which are the highest values reported for rare earth doped SrTiO3.

  10. Homogeneity and variation of donor doping in Verneuil-grown SrTiO3:Nb single crystals

    Science.gov (United States)

    Rodenbücher, C.; Luysberg, M.; Schwedt, A.; Havel, V.; Gunkel, F.; Mayer, J.; Waser, R.

    2016-08-01

    The homogeneity of Verneuil-grown SrTiO3:Nb crystals was investigated. Due to the fast crystal growth process, inhomogeneities in the donor dopant distribution and variation in the dislocation density are expected to occur. In fact, for some crystals optical studies show variations in the density of Ti3+ states on the microscale and a cluster-like surface conductivity was reported in tip-induced resistive switching studies. However, our investigations by TEM, EDX mapping, and 3D atom probe reveal that the Nb donors are distributed in a statistically random manner, indicating that there is clearly no inhomogeneity on the macro-, micro-, and nanoscale in high quality Verneuil-grown crystals. In consequence, the electronic transport in the bulk of donor-doped crystals is homogeneous and it is not significantly channelled by extended defects such as dislocations which justifies using this material, for example, as electronically conducting substrate for epitaxial oxide film growth.

  11. Nickel-ceria infiltrated Nb-doped SrTiO3 for low temperature SOFC anodes and analysis on gas diffusion impedance

    DEFF Research Database (Denmark)

    Abdul Jabbar, Mohammed Hussain; Høgh, Jens Valdemar Thorvald; Jacobsen, Torben

    2012-01-01

    This report concentrates on high performance anodes appropriate for SOFCs operating at low temperatures (400–600 °C). Symmetrical cells were made by screen printing of Nb-doped SrTiO3 (STN) on both sides of a dense ScYSZ electrolyte. Backbones I (36% porosity) and II (47% porosity) were obtained ...

  12. Science Letters: Chemically processed Nb-doped SrTiO3 films and properties

    Institute of Scientific and Technical Information of China (English)

    YIN Ming-zhi

    2006-01-01

    Homogeneous, crack-free SrNbxTi1-xO3 thin films on (110) silicon substrates were successfully fabricated by sol-gel processing. The optimum route and conditions were systematically investigated. Sr(OAc)2 glacial acetic acid solution, after being refluxed and reacted with tartrate, formed Sr(OAc)2(C4H6O6)2; Ti(OBu)4 formed Ti(OAc)4-x(AcAc)x after having the ligand partially exchanged with AcAc, while Nb(OC2H5)5 formed (OAc)2Nb(AcAc)(C4H6O6) by exchanging of ligand in glacial acetic acid with (CH3CO)2O. All the metal species after undergoing partial hydrolysis and polymerization with hydroxyl or oxygen,formed SrNbxTi1-xO3 cluster sol. Methyl cellulose (MCL) caused SrNbxTi1-xO3 sol to have polymeric structure and easily form films. SrNbxTi1-xO3 films with perovskite were subsequently formed after being annealed at 650~750 ℃ for 60 min in 25% N2+75% H2 (volume ratio) atmosphere. Resistivity of the SrNb0.1Ti0.9O3 films at room temperature was 64μΩ.cm, a particular T2 temperature dependence of the resistivity, from 25 K up to room temperature, was observed.

  13. Homogeneity and variation of donor doping in Verneuil-grown SrTiO3:Nb single crystals

    OpenAIRE

    Rodenbücher, C.; Luysberg, M; Schwedt, A.; V. Havel; Gunkel, F.; Mayer, J; WASER, R

    2016-01-01

    The homogeneity of Verneuil-grown SrTiO3:Nb crystals was investigated. Due to the fast crystal growth process, inhomogeneities in the donor dopant distribution and variation in the dislocation density are expected to occur. In fact, for some crystals optical studies show variations in the density of Ti3+ states on the microscale and a cluster-like surface conductivity was reported in tip-induced resistive switching studies. However, our investigations by TEM, EDX mapping, and 3D atom probe re...

  14. Sintering and Electrical Characterization of La and Nb Co‐doped SrTiO3 Electrode Materials for Solid Oxide Cell Applications

    DEFF Research Database (Denmark)

    Sudireddy, Bhaskar Reddy; Agersted, Karsten

    2014-01-01

    Single‐phase lanthanum and niobium co‐doped strontium titanate (Sr1–3x/2LaxTi0.9Nb0.1O3; x = 0–0.02) ceramics were prepared. Dilatometry in reducing atmosphere showed an increase in the sintering rate and sintered density with an increase in La amount. Microscopy of fractured surfaces of sintered...... observed at lower temperatures. These observations demonstrate the flexibility in tailoring the microstructure and electronic transport properties by doping small amounts of La into the Nb‐doped SrTiO3 and show that Sr1–3x/2LaxTi0.9Nb0.1O3 is a potential electrode material for solid oxide cells....

  15. Microstructural and electrical characterization of Nb-doped SrTiO3–YSZ composites for solid oxide cell electrodes

    DEFF Research Database (Denmark)

    Reddy Sudireddy, Bhaskar; Blennow Tullmar, Peter; Nielsen, Karsten Agersted

    2012-01-01

    Nb-doped SrTiO3 (Sr1 − xTi0.9Nb0.1O3, x = 0.01 and 0.06, henceforth known as STN) and 8 mol% Y2O3 stabilized ZrO2 (8YSZ) composites were prepared by mixing them in different volume fractions between 10 vol.% and 50 vol.% of 8YSZ. The composites were compacted into pellets, sintered and evaluated...... phases. However, microstructural analysis revealed segregation and formation of Nb enriched particles in the 50 vol.% 8YSZ composite. Chemical analysis by energy dispersive spectroscopy (EDS) also showed the inter-diffusion of elements (especially Ti from STN and Zr from 8YSZ) from both phases on small...

  16. Resistive switching phenomena of extended defects in Nb-doped SrTiO$_{3}$ under influence of external gradients

    OpenAIRE

    Rodenbücher, Christian

    2014-01-01

    Redox-based memristive materials have attracted much attention in the last decade owing to theirability to change the resistance upon application of an electric field making them promising candidatesfor future non-volatile memories. However, a fundamental understanding of the nature ofthe resistive switching effect, which is indispensable for designing future technological applications,is still lacking.As a prototype material of a memristive oxide, strontium titanate (SrTiO3) has been investi...

  17. Contrasting conduction mechanisms of two internal barrier layer capacitors: (Mn, Nb)-doped SrTiO3 and CaCu3Ti4O12

    Science.gov (United States)

    Tsuji, Kosuke; Chen, Wei-Ting; Guo, Hanzheng; Lee, Wen-Hsi; Guillemet-Fritsch, Sophie; Randall, Clive A.

    2017-02-01

    The d.c. conduction is investigated in the two different types of internal barrier layer capacitors, namely, (Mn, Nb)-doped SrTiO3 (STO) and CaCu3Ti4O12 (CCTO). Scanning electron microscopy (SEM) and Capacitance - Voltage (C-V) analysis are performed to estimate the effective electric field at a grain boundary, EGB. Then, the d.c. conduction mechanism is discussed based on the J (Current density)-EGB characteristics. Three different conduction mechanisms are successively observed with the increase of EGB in both systems. In (Mn, Nb)-doped STO, non-linear J-EGB characteristics is temperature dependent at the intermediate EGB and becomes relatively insensitive to the temperature at the higher EGB. The J- EGB at each regime is explained by the Schottky emission (SE) followed by Fowler-Nordheim (F-N) tunneling. Based on the F-N tunneling, the breakdown voltage is then scaled by the function of the depletion layer thickness and Schottky barrier height at the average grain boundary. The proposed function shows a clear linear relationship with the breakdown. On the other hand, F-N tunneling was not observed in CCTO in our measurement. Ohmic, Poole-Frenkel (P-F), and SE are successively observed in CCTO. The transition point from P-F and SE depends on EGB and temperature. A charge-based deep level transient spectroscopy study reveals that 3 types of trap states exist in CCTO. The trap one with Et ˜ 0.65 eV below the conduction band is found to be responsible for the P-F conduction.

  18. Self-powered sensitive and stable UV-visible photodetector based on GdNiO3/Nb-doped SrTiO3 heterojunctions

    Science.gov (United States)

    Wang, Le; Chang, Lei; Yin, Xinmao; You, Lu; Zhao, Jia-Li; Guo, Haizhong; Jin, Kuijuan; Ibrahim, Kurash; Wang, Jiaou; Rusydi, Andrivo; Wang, Junling

    2017-01-01

    The properties of perovskite nickelates are very sensitive to their oxygen content, which allows us to tune their electronic structures by varying the oxygen partial pressure during film deposition. Under the optimized condition, we have obtained GdNiO3 films that are sensitive to a wide spectrum of light. By combining the GdNiO3 film with Nb-doped SrTiO3 to form a heterojunction, we design a self-powered photodetector with high sensitivity toward light with a wavelength between 650 nm and 365 nm. Under 365 nm illumination (50 μW/cm2), the device shows a responsivity of 0.23 A/W at 0 V bias, comparable to or even better than the ultraviolet photodetectors made of semiconductor materials such as GaN or ZnO. The photo-dark ratio can be close to 103 when the power light density reaches 0.6 mW/cm2. Moreover, the device performance is very stable without any decay after 6 months.

  19. Ferroelectric domain structures of epitaxial CaBi2Nb2O9 thin films on single crystalline Nb doped (1 0 0) SrTiO3 substrates

    Science.gov (United States)

    Ahn, Yoonho; Seo, Jeong Dae; Son, Jong Yeog

    2015-07-01

    Epitaxial CaBi2Nb2O9 (CBNO) thin films were deposited on Nb-doped SrTiO3 substrates. The CBNO thin films as a lead-free ferroelectric material exhibit a good ferroelectric property with the remanent polarization of 10.6 μC/cm2. In the fatigue resistance test, the CBNO thin films have no degradation in polarization up to 1×1012 switching cycles, which is applicable for non-volatile ferroelectric random access memories (FeRAMs). Furthermore, piezoresponse force microscopy study (PFM) reveals that the CBNO thin films have larger ferroelectric domain structures than those of PbTiO3 thin films. From the Landau, Lifshiftz, and Kittel's scaling law, it is inferred that the domain wall energy of CBNO thin films is probably very similar to that of the PbTiO3 thin films.

  20. Colossal Magnetoresistive p-n Junctions of Te-Doped LaMnO3/Nb-doped SrTiO3

    Institute of Scientific and Technical Information of China (English)

    Lü Hui-Bin; YANG Guo-Zhen; DAI Shou-Yu; CHEN Zheng-Hao; LIU Li-feng; GUO Hai-Zhong; XIANG Wen-Feng; FEI Yi-Yan; HE Meng; ZHOU Yue-Liang

    2003-01-01

    We have fabricated colossal magnetoresistive (CMR) p-n junctions made of Te-doped LaMnOs and Nb-doped SrTiOa with laser molecular beam epitaxy. The I - V characteristics of the Lao.aTeo.iMnOs/SrNfao.oiTio.ggOs p-n junctions as a function of applied magnetic field (0-5 T) were experimentally studied in the temperature range 77-300 K. The results indicate that the p-n junction exhibited the CMR behaviour. The magnetoresistance (MR) is positive at 220 K and 300 K, while it displays a negative MR at 77K. For a positive bias, the MR ratios (&.R/RO, Afl = RH - Ro) are 7.5% at 0.1 T and 18% at 5T for 300K, 5% at 0.1 T and 33% at 5T for 220K, -14% at 0.1 T and -71% at 5 T for 77K. For a negative bias, the MR ratios are 6.3% at 0.1 T and 10.8% at 3T for 300K, 5.1% at 0.1 T and 15% at 3T for 220K, -19% at 0.1 T and -72% at 5 T for 77K. The CMR behaviour of the p-n junction is different from those of the LaMnOa compound family.

  1. Rotation of ferromagnetic clusters induced magnetoresistance in the junction composed of La0.9Ca0.1MnO3+δ and 1 wt.% Nb-doped SrTiO3

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A junction composed of ultrathin La0.gCa0.1MnO3+δ (LCMO) film and 1 wt.% Nb-doped SrTiO3 was fabricated and its magnetoresistance (MR) was studied and compared with LCMO film. It was found that the resistance of the junction has a similar dependence on magnetic field as that of the LCMO film: the curvature of R-H curves is upward above Curie temperature (To) and downward below TC. These behaviours strongly suggest that the rotation of ferromagnetic clusters in manganite also causes MR in the corresponding junction. This MR can be qualitatively understood by the change of the width of the barrier induced by the rotation of ferromagnetic clusters. These results suggest a possibility to obtain junctions with large low-field MR.

  2. Impulse voltage control of continuously tunable bipolar resistive switching in Pt/Bi0.9Eu0.1FeO3/Nb-doped SrTiO3 heterostructures

    Science.gov (United States)

    Wei, Maocai; Liu, Meifeng; Wang, Xiuzhang; Li, Meiya; Zhu, Yongdan; Zhao, Meng; Zhang, Feng; Xie, Shuai; Hu, Zhongqiang; Liu, Jun-Ming

    2017-03-01

    Epitaxial Bi0.9Eu0.1FeO3 (BEFO) thin films are deposited on Nb-doped SrTiO3 (NSTO) substrates by pulsed laser deposition to fabricate the Pt/BEFO/NSTO (001) heterostructures. These heterostructures possess bipolar resistive switching, where the resistances versus writing voltage exhibits a distinct hysteresis loop and a memristive behavior with good retention and anti-fatigue characteristics. The local resistive switching is confirmed by the conductive atomic force microscopy (C-AFM), suggesting the possibility to scale down the memory cell size. The observed memristive behavior could be attributed to the ferroelectric polarization effect, which modulates the height of potential barrier and width of depletion region at the BEFO/NSTO interface. The continuously tunable resistive switching behavior could be useful to achieve non-volatile, high-density, multilevel random access memory with low energy consumption.

  3. Carrier tuning the metal-insulator transition of epitaxial La0.67Sr0.33MnO3 thin film on Nb doped SrTiO3 substrate

    Directory of Open Access Journals (Sweden)

    J. M. Zhan

    2016-04-01

    Full Text Available La0.67Sr0.33MnO3 (LSMO thin films were deposited on (001SrTiO3(STO and n-type doped Nb:SrTiO3(NSTO single crystal substrates respectively. The metal to insulator transition temperature(TMI of LSMO film on NSTO is lower than that on STO, and the TMI of LSMO can be tuned by changing the applied current in the LSMO/NSTO p-n junction. Such behaviors were considered to be related to the carrier concentration redistribution in LSMO film caused by the change of depletion layer thickness in p-n junction which depends greatly on the applied electric field. The phenomenon could be used to configure artificial devices and exploring the underlying physics.

  4. Probing hot electron transport across an epitaxial Schottky interface of SrRuO3/Nb : SrTiO3

    NARCIS (Netherlands)

    Roy, S.; Kamerbeek, A. M.; Rana, K. G.; Parui, S.; Banerjee, T.

    2013-01-01

    SrRuO3 (SRO), a conducting transition metal oxide, is commonly used for engineering domains in BiFeO3. Oxide devices can be envisioned by integrating SRO with an oxide semiconductor as Nb doped SrTiO3 (Nb:STO). Using a three-terminal device configuration, we study vertical transport in a SRO/Nb:STO

  5. Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection.

    Science.gov (United States)

    Kundu, Souvik; Clavel, Michael; Biswas, Pranab; Chen, Bo; Song, Hyun-Cheol; Kumar, Prashant; Halder, Nripendra N; Hudait, Mantu K; Banerji, Pallab; Sanghadasa, Mohan; Priya, Shashank

    2015-07-23

    We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance, and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction, and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials.

  6. Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection

    Science.gov (United States)

    Kundu, Souvik; Clavel, Michael; Biswas, Pranab; Chen, Bo; Song, Hyun-Cheol; Kumar, Prashant; Halder, Nripendra N.; Hudait, Mantu K.; Banerji, Pallab; Sanghadasa, Mohan; Priya, Shashank

    2015-07-01

    We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance, and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction, and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials.

  7. Thermoelectric performance enhancement of SrTiO3 by Pr doping

    KAUST Repository

    Kahaly, M. Upadhyay

    2014-01-01

    We investigate Pr doping at the Sr site as a possible route to enhance the thermoelectric behavior of SrTiO3-based materials, using first principles calculations in full-potential density functional theory. The effects of the Pr dopant on the local electronic structure and resulting transport properties are compared to common Nb doping. We demonstrate a substantial enhancement of the thermoelectric figure of merit and develop an explanation for the positive effects, which opens new ways for materials optimization by substitutional doping at the perovskite B site. © 2014 the Partner Organisations.

  8. Rational design of mixed ionic and electronic conducting perovskite oxides for solid oxide fuel cell anode materials: A case study for doped SrTiO3

    Energy Technology Data Exchange (ETDEWEB)

    Suthirakun, Suwit; Xiao, Guoliang; Ammal, Salai Cheettu; Chen, Fanglin; zur Loye, Hans-Conrad; Heyden, Andreas

    2014-01-01

    The effect of p- and n-type dopants on ionic and electronic conductivity of SrTiO3 based perovskites were investigated both computationally and experimentally. Specifically, we performed density functional theory (DFT) calculations of Na- and La-doped SrTiO3 and Na- and Nb-doped SrTiO3 systems. Constrained ab initio thermodynamic calculations were used to evaluate the phase stability and reducibility of doped SrTiO3 under both oxidizing and reducing synthesis conditions, as well as under anodic solid oxide fuel cell (SOFC) conditions. The density of states (DOS) of these materials was analyzed to study the effects of p- and n-doping on the electronic conductivity. Furthermore, Na- and La-doped SrTiO3 and Na- and Nb-doped SrTiO3 samples were experimentally prepared and the conductivity was measured to confirm our computational predictions. The experimental observations are in very good agreement with the theoretical predictions that doping n-doped SrTiO3 with small amounts of p-type dopants promotes both the ionic and electronic conductivity of the material. This doping strategy is valid independent of p- and n-doping site and permits the synthesis of perovskite based mixed ionic/electronic conductors.

  9. Solvothermal Synthesis and Photocatalytic Properties of Nitrogen-Doped SrTiO3 Nanoparticles

    Directory of Open Access Journals (Sweden)

    Uyi Sulaeman

    2010-01-01

    Full Text Available Perovskite-type nitrogen-doped SrTiO3 nanoparticles of 50–80 nm in diameter were successfully synthesized by the solvothermal of Ti(OC3H74, SrCl2⋅6H2O, and hexamethylenetetramine in KOH aqueous solution. Nitrogen-doped SrTiO3 showed excellent photocatalytic activity under both UV and visible light irradiation, that is, the photocatalytic activity of N-doped SrTiO3 for DeNOx reaction was greater than that of SrTiO3 and commercial TiO2 (Degussa P25 in both visible light region (>510 nm and UV light region (>290 nm. The excellent visible light photocatalytic activity of this substance was caused by generating a new band gap that absorbs visible light.

  10. Synthesis of BiFeO3 thin films on single-terminated Nb : SrTiO3 (111 substrates by intermittent microwave assisted hydrothermal method

    Directory of Open Access Journals (Sweden)

    Ivan Velasco-Davalos

    2016-06-01

    Full Text Available We report on a simple and fast procedure to create arrays of atomically flat terraces on single crystal SrTiO3 (111 substrates and the deposition of ferroelectric BiFeO3 thin films on such single-terminated surfaces. A microwave-assisted hydrothermal method in deionized water and ammonia solution selectively removes either (SrO34− or Ti4+ layers to ensure the same chemical termination on all terraces. Measured step heights of 0.225 nm (d111 and uniform contrast in the phase image of the terraces confirm the single termination in pure and Nb doped SrTiO3 single crystal substrates. Multiferroic BiFeO3 thin films were then deposited by the same microwave assisted hydrothermal process on Nb : SrTiO3 (111 substrates. Bi(NO33 and Fe(NO33 along with KOH served as the precursors solution. Ferroelectric behavior of the BiFeO3 films on Nb : SrTiO3 (100 substrates was verified by piezoresponse force microscopy.

  11. Photocatalytic degradation of methylene blue dye under visible light over Cr doped strontium titanate (SrTiO3) nanoparticles.

    Science.gov (United States)

    Qazi, Inamur Rahman; Lee, Woo-Jin; Lee, Hyun-Cheol; Hassan, Mallick Shamshi; Yang, O-Bong

    2010-05-01

    Strontium titanate (SrTiO3) and chromium doped SrTiO3 (Cr/SrTiO3) were prepared by modified sol-gel method with the citric acid as a chelating agent in the ethylene glycol solution for the effective photodegradation of methylene blue dye under visible light irradiation. The synthesized doped and un-doped SrTiO3 nanoparticles were structurally characterized and their photoresponse performances for the efficient degradation of methylene blue dye have been demonstrated. After introducing the Cr on SrTiO3, UV-Vis absorption was appeared the red-shift at 566 nm from 392 nm as compare with bare SrTiO3. The photocatalytic degradation activity of Cr/SrTiO3 was significantly improved to 60% degradation of methylene blue in 3 h under visible light, which is approximately 5 times higher than that of the bare SrTiO3.

  12. Influence of rare earth doping on thermoelectric properties of SrTiO3 ceramics

    Science.gov (United States)

    Liu, J.; Wang, C. L.; Li, Y.; Su, W. B.; Zhu, Y. H.; Li, J. C.; Mei, L. M.

    2013-12-01

    Thermoelectric properties of SrTiO3 ceramics, doped with different rare earth elements, were investigated in this work. It's found that the ionic radius of doping elements plays an important role on thermoelectric properties: SrTiO3 ceramics doped with large rare earth ions (such as La, Nd, and Sm) exhibit large power factors, and those doped with small ions (such as Gd, Dy, Er, and Y) exhibit low thermal conductivities. Therefore, a simple approach for enhancing the thermoelectric performance of SrTiO3 ceramics is proposed: mainly doped with large ions to obtain a large power factor and, simultaneously, slightly co-doped with small ions to obtain a low thermal conductivity. Based on this rule, Sr0.8La0.18Yb0.02TiO3 ceramics were prepared, whose ZT value at 1 023 K reaches 0.31, increasing by a factor of 19% compared with the single-doped counterpart Sr0.8La0.2TiO3 (ZT = 0.26).

  13. Electronic properties of Cr-, B-doped and codoped SrTiO3

    Science.gov (United States)

    Maldonado, Frank; Maza, Luz; Stashans, Arvids

    2017-01-01

    Spin-polarized density functional theory (DFT) computations have been carried out to investigate Cr-, B-doping as well as codoping in the SrTiO3 crystal. Impact of the oxygen vacancy as an intrinsic point defect has been also taken into consideration. In order to describe more precisely 3d electrons of the Ti and Cr atoms, Hubbard-like U term in the DFT has been introduced. Outcomes of the calculations reveal occupied states within the forbidden energy region arguing that these in-gap states might be responsible for visible light photocatalysis in the SrTiO3. Structural and magnetic features of the doped and codoped material are discussed as well.

  14. Microstructure and dynamics of vacancy-induced nanofilamentary switching network in donor doped SrTiO3-x memristors

    Science.gov (United States)

    Nili, Hussein; Ahmed, Taimur; Walia, Sumeet; Ramanathan, Rajesh; Esmaielzadeh Kandjani, Ahmad; Rubanov, Sergey; Kim, Jeeson; Kavehei, Omid; Bansal, Vipul; Bhaskaran, Madhu; Sriram, Sharath

    2016-12-01

    Donor doping of perovskite oxides has emerged as an attractive technique to create high performance and low energy non-volatile analog memories. Here, we examine the origins of improved switching performance and stable multi-state resistive switching in Nb-doped oxygen-deficient amorphous SrTiO3 (Nb:a-STO x ) metal-insulator-metal (MIM) devices. We probe the impact of substitutional dopants (i.e., Nb) in modulating the electronic structure and subsequent switching performance. Temperature stability and bias/time dependence of the switching behavior are used to ascertain the role of substitutional dopants and highlight their utility to modulate volatile and non-volatile behavior in a-STO x devices for adaptive and neuromorphic applications. We utilized a combination of transmission electron microscopy, photoluminescence emission properties, interfacial compositional evaluation, and activation energy measurements to investigate the microstructure of the nanofilamentary network responsible for switching. These results provide important insights into understanding mechanisms that govern the performance of donor-doped perovskite oxide-based memristive devices.

  15. Infrared Optical Absorption in Low-spin Fe2+-doped SrTiO3

    Energy Technology Data Exchange (ETDEWEB)

    Comes, Ryan B.; Kaspar, Tiffany C.; Heald, Steve M.; Bowden, Mark E.; Chambers, Scott A.

    2016-01-06

    Band gap engineering in SrTiO3 and related titanate perovskites has long been explored due to the intriguing properties of the materials for photocatalysis and photovoltaic applications. A popular approach in the materials chemistry community is to substitutionally dope aliovalent transition metal ions onto the B site in the lattice to alter the valence band. However, in such a scheme there is limited control over the dopant valence, and compensating defects often form. Here we demonstrate a novel technique to controllably synthesize Fe2+- and Fe3+-doped SrTiO3 thin films without formation of compensating defects by co-doping with La3+ ions on the A site. We stabilize Fe2+-doped films by doping with two La ions for every Fe dopant, and find that the Fe ions exhibit a low-spin electronic configuration, producing optical transitions in the near infrared regime and degenerate doping. The novel electronic states observed here offer a new avenue for band gap engineering in perovskites for photocatalytic and photovoltaic applications.

  16. Site-specific doping, tunable dielectric properties and intrinsic paramagnetism in Mn-doped SrTiO3

    Indian Academy of Sciences (India)

    D Choudhury

    2015-06-01

    Mn doping in SrTiO3 leads to the emergence of qualitatively distinct and novel physical properties. We show that Mn ions can be controllably doped at either of the perovskite (Sr) or (Ti) site as well as at both sites simultaneously and the resultant physical properties depend intimately on the particular dopant site. We critically review the recent literature on various Mn-doped SrTiO3 systems, which includes reports of dielectric glass, spin-glass and ferromagnetism and by combining experiments with first-principles calculations, we demonstrate that depending on the particular dopant site for Mn ions, the dielectric properties can be widely tuned from a quantum paraelectric to a dielectric glass. However, the intrinsic magnetism in all these cases remains essentially paramagnetic for phase-pure systems.

  17. Gd-doping-induced insulator-metal transition in SrTiO3

    Science.gov (United States)

    Gu, Yanni; Xu, Sheng; Wu, Xiaoshan

    2017-01-01

    Recently, insulator-metal transition was found experimentally in Gd-doped SrTiO3 films. Here, we present first-principle investigation on the structural, electronic and magnetic properties of Sr1-xGdxTiO3 within density-function theory. The spin-polarized calculations give a diamagnetic insulator at x=0, a ferrimagnetic metal 0.125≤ x≤0.5 and a ferrimagnetic insulator x=1 and all Ti ions moments are antiparallel to Gd ions moments. Magnetic Gd-doping distorts the structures of Sr1-xGdxTiO3 films and results in ferrimagnetism. Doped electrons occupy the bottom of conduction bands so that insulator-metal transition occurs. These calculated results are in agreement with available experiments.

  18. Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

    Institute of Scientific and Technical Information of China (English)

    Zhang Chao; Wang Chun-Lei; Li Ji-Chao; Yang Kun

    2007-01-01

    We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8 eV and 6.5 eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrTiO3, but the gap changes from Г-R point to Г-X point.

  19. Plasmon mediated cathodic photocurrent generation in sol-gel synthesized doped SrTiO3 nanofilms

    Directory of Open Access Journals (Sweden)

    Ramu Pasupathi Sugavaneshwar

    2015-11-01

    Full Text Available Thin films of SrTiO3 (STO and Rh-doped SrTiO3 (Rh-STO were synthesized by sol-gel method and loaded with Ag nanoparticles. Pristine STO films exhibited anodic photocurrent while Rh-STO exhibited cathodic photocurrent. An enhancement in the overall cathodic photocurrent is observed with Ag nanoparticle loading and an additional enhancement in the visible light range is seen from the incident photon-to-current efficiency spectrum due to synergetic effect of Rh doping and Ag loading in STO.

  20. Observation of the quantum Hall effect in δ-doped SrTiO3.

    Science.gov (United States)

    Matsubara, Y; Takahashi, K S; Bahramy, M S; Kozuka, Y; Maryenko, D; Falson, J; Tsukazaki, A; Tokura, Y; Kawasaki, M

    2016-05-27

    The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system. The two-dimensional electron system in SrTiO3 has sparked a great deal of interest, mainly because of the strong electron correlation effects expected from the 3d orbitals. Here we report the observation of the quantum Hall effect in a dilute La-doped SrTiO3-two-dimensional electron system, fabricated by metal organic molecular-beam epitaxy. The quantized Hall plateaus are found to be solely stemming from the low Landau levels with even integer-filling factors, ν=4 and 6 without any contribution from odd ν's. For ν=4, the corresponding plateau disappears on decreasing the carrier density. Such peculiar behaviours are proposed to be due to the crossing between the Landau levels originating from the two subbands composed of d orbitals with different effective masses. Our findings pave a way to explore unprecedented quantum phenomena in d-electron systems.

  1. Photocatalytic Destruction of Nitrogen Monoxide over La3+ and N Co-doped SrTiO3 Powders under Visible Light Irradiation

    Institute of Scientific and Technical Information of China (English)

    王金淑; 马淑云; 王国红

    2004-01-01

    Lanthanum and nitrogen co-doped SrTiO3 was prepared by a mechanochemical reaction using SrTiO3, urea and La2O3 as the raw materials. The samples were characterized by X-ray diffraction, X-ray photoelectron spectrometer, transmission electron microscopy, and nitrogen adsorption-desorption isotherm measurements. Lanthanum doping could increase the doping content of nitrogen in the sample. The sample prepared with 0.2 mol% La2O3, 22 mol% urea and 77.8 mol% SrTiO3 by mechanochemical reaction, which has nearly the same nitrogen and lanthanum doping fractions, exhibited high photocatalytic activities. Under the irradiation of light with wavelength larger than 400, and 290 nm, the photocatalytic activity of nitrogen and lanthanum co-doped SrTiO3 were 2.6 and 2 times greater than that of pure SrTiO3.

  2. Dielectric Properties and Defect Structure of Bi-doped SrTiO3 Ceramics

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The dielectric properties of ceramics with composition of (Sr1-xBix)TiO3+x/2(where x=0.05~0.70 ) were measured at frequency of 1 MHz. The experimental results indicate that the dielectric properties of (Sr1-xBix)TiO3+x/2 system are greatly varied with an increase of the stoichiometric amounts of Bi2O3. The relative permittivity of the solid solutions is high, and the dissipation factor is low. The positron annihilation technique(PAT) was adopted to study the defect structure. An explanation of the dielectric properties of Bi-doped SrTiO3 ceramics has been suggested in terms of electron-compensation and vacancy or defect-compensation mechanisms and space-charge polarization mechanism.

  3. 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.

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

    Science.gov (United States)

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

    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.

  5. Study on electrical properties of Ni-doped SrTiO3 ceramics using impedance spectroscopy

    Indian Academy of Sciences (India)

    S K Rout; S Panigrahi; J Bera

    2005-06-01

    The ceramics, SrTiO3 (ST) and 0.4, 0.8 atom% Ni doped SrTiO3, were prepared by solid state reaction route. The average grain size of undoped and doped samples was measured and found to be 1.2, 1.9 and 3.7 m, respectively. The impedance measurements were conducted at 400–600°C to separate grain and grain boundary contributions. The grain and grain boundaries relaxation frequencies were shifted to higher frequency with temperature. Bulk resistance of doped and undoped ST ceramics was more or less the same. Single grain boundary resistance of doped sample was higher than that of undoped one, indicating that GB resistance increases with acceptor doping. Activation energies were calculated to confirm the same.

  6. Electronic structure and optical properties of In-doped SrTiO3 by density function theory

    Institute of Scientific and Technical Information of China (English)

    Zhang Zhi-Yong; Yun Jiang-Ni; Zhang Fu-Chun

    2007-01-01

    The effect of In doping on the electronic structure and optical properties of SrTiO3 is investigated by the firstprinciples calculation of plane wave ultra-soft pseudo-potential based on the density function theory (DFT). The calculated results reveal that due to the hole doping, the Fermi level shifts into valence bands (VBs) for SrTi1-xInxO3 with x = 0.125 and the system exhibits p-type degenerate semiconductor features. It is suggested according to the density of states (DOS) of SrTi0.s75In0.125O3 that the band structure of p-type SrTiO3 can be described by a rigid band model.At the same time, the DOS shifts towards high energies and the optical band gap is broadened. The wide band gap,small transition probability and weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the optical transparency of the film. The optical transmittance of In doped SrTiO3 is higher than 85% in a visible region, and the transmittance improves greatly. And the cut-off wavelength shifts into a blue-light region with the increase of In doping concentration.

  7. Defect mechanisms of coloration in Fe-doped SrTiO3 from first principles

    Science.gov (United States)

    Baker, Jonathon N.; Bowes, Preston C.; Long, Daniel M.; Moballegh, Ali; Harris, Joshua S.; Dickey, Elizabeth C.; Irving, Douglas L.

    2017-03-01

    To understand the underlying defect mechanisms governing the coloration of Fe-doped SrTiO3 (Fe:STO), density functional theory calculations were used to determine defect formation energies and to interpret optical absorption spectra. A grand canonical defect equilibrium model was developed using the calculated formation energies, which enabled connection to annealing experiments. It was found that FeTi 0 is stable in oxidizing conditions and leads to the optical absorption signatures in oxidized Fe:STO, consistent with experiment. Fe:STO was found to transition from brown to transparent as P O2 was reduced during annealing. The defect equilibrium model reproduces a consistent P O2 of this coloration transition. Most critical to reproducing the P O2 of the coloration transition was inclusion of a Fe Ti - V O first nearest neighbor complex, which was found to be strongly interacting. The coloration transition P O2 was found to be insensitive to the presence of minority background impurities, slightly sensitive to Fe content, and more sensitive to annealing temperature.

  8. Oxygen partial pressure dependence of surface space charge formation in donor-doped SrTiO3

    Science.gov (United States)

    Andrä, Michael; Dvořák, Filip; Vorokhta, Mykhailo; Nemšák, Slavomír; Matolín, Vladimír; Schneider, Claus M.; Dittmann, Regina; Gunkel, Felix; Mueller, David N.; Waser, Rainer

    2017-05-01

    In this study, we investigated the electronic surface structure of donor-doped strontium titanate. Homoepitaxial 0.5 wt. % donor-doped SrTiO3 thin films were analyzed by in situ near ambient pressure X-ray photoelectron spectroscopy at a temperature of 770 K and oxygen pressures up to 5 mbar. Upon exposure to an oxygen atmosphere at elevated temperatures, we observed a rigid binding energy shift of up to 0.6 eV towards lower binding energies with respect to vacuum conditions for all SrTiO3 core level peaks and the valence band maximum with increasing oxygen pressure. The rigid shift is attributed to a relative shift of the Fermi energy towards the valence band concomitant with a negative charge accumulation at the surface, resulting in a compensating electron depletion layer in the near surface region. Charge trapping effects solely based on carbon contaminants are unlikely due to their irreversible desorption under the given experimental conditions. In addition, simple reoxygenation of oxygen vacancies can be ruled out as the high niobium dopant concentration dominates the electronic properties of the material. Instead, the negative surface charge may be provided by the formation of cation vacancies or the formation of charged oxygen adsorbates at the surface. Our results clearly indicate a pO2-dependent surface space charge formation in donor-doped SrTiO3 in oxidizing conditions.

  9. High photocatalytic activity of V-doped SrTiO3 porous nanofibers produced from a combined electrospinning and thermal diffusion process

    Directory of Open Access Journals (Sweden)

    Panpan Jing

    2015-06-01

    Full Text Available In this letter, we report a novel V-doped SrTiO3 photocatalyst synthesized via electrospinning followed by a thermal diffusion process at low temperature. The morphological and crystalline structural investigations reveal not only that the V-doped SrTiO3 photocatalyst possesses a uniform, porous, fibrous structure, but also that some V5+ ions are introduced into the SrTiO3 lattice. The photocatalytic capability of V-doped SrTiO3 porous nanofibers was evaluated through photodegrading methyl orange (MO in aqueous solution under artificial UV–vis light. The results indicated that V-doped SrTiO3 porous nanofibers have excellent catalytic efficiency. Furthermore, the excellent catalytic activity was maintained even after five cycle tests, indicating that they have outstanding photocatalytic endurance. It is suggested that the excellent photocatalytic performance of doped SrTiO3 nanofibers is possibly attributed to the V5+ ion doping increasing the light utilization as well as to the outstanding porous features, the excellent component and structure stability.

  10. Variation in superconducting transition temperature due to tetragonal domains in two-dimensionally doped SrTiO3

    Science.gov (United States)

    Noad, Hilary; Spanton, Eric M.; Nowack, Katja C.; Inoue, Hisashi; Kim, Minu; Merz, Tyler A.; Bell, Christopher; Hikita, Yasuyuki; Xu, Ruqing; Liu, Wenjun; Vailionis, Arturas; Hwang, Harold Y.; Moler, Kathryn A.

    2016-11-01

    Strontium titanate is a low-temperature, non-Bardeen-Cooper-Schrieffer superconductor that superconducts to carrier concentrations lower than in any other system and exhibits avoided ferroelectricity at low temperatures. Neither the mechanism of superconductivity in strontium titanate nor the importance of the structure and dielectric properties for the superconductivity are well understood. We studied the effects of twin structure on superconductivity in a 5.5-nm-thick layer of niobium-doped SrTiO3 embedded in undoped SrTiO3. We used a scanning superconducting quantum interference device susceptometer to image the local diamagnetic response of the sample as a function of temperature. We observed regions that exhibited a superconducting transition temperature Tc≳ 10 % higher than the temperature at which the sample was fully superconducting. The pattern of these regions varied spatially in a manner characteristic of structural twin domains. Some regions are too wide to originate on twin boundaries; therefore, we propose that the orientation of the tetragonal unit cell with respect to the doped plane affects Tc. Our results suggest that the anisotropic dielectric properties of SrTiO3 are important for its superconductivity and need to be considered in any theory of the mechanism of the superconductivity.

  11. 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.

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

    OpenAIRE

    Jin, K. X.; Li, Y. F.; Wang, Z. L.; Peng, H. Y.; W. N. Lin; A. K. K. Kyaw; Jin, Y. L.; Jin, K. J.; Sun, X. W.; Soci, C.; Tom Wu

    2012-01-01

    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 ...

  13. The electronic and optical properties of carbon-doped SrTiO3: Density functional characterization

    Directory of Open Access Journals (Sweden)

    N. Li

    2012-09-01

    Full Text Available The electronic properties and optical activities of C-doped cubic SrTiO3 in perovskite structure are studied by first-principles calculation. The calculated formation energies show that the substitutional C impurity is preferentially occupied at the Ti site. For C@O, the C impurity introduces spin-polarized gap states, and the associated electron excitations among the valence band, the conduction band and the gap states produce various visible-light absorption thresholds. For C@Ti, some C gap states of s-character appear near the bottom of the conduction band, which result in the lowered optical transition energy and thus the visible light absorption as observed in the experiment.

  14. 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.

  15. Magnetic field-induced bipolar resistive switching and negative differential resistance in (110)SrTiO3:Nb/ZnO heterojunctions

    Science.gov (United States)

    Fang, Yinglong; Li, Jiachen; Chen, Yonghai; Zhang, Weifeng; Jia, Caihong

    2017-09-01

    (110)SrTiO3:Nb (NSTO)/ZnO heterojunctions were fabricated by magnetron sputtering. The NSTO/ZnO heterojunctions exhibit a typical rectification characteristic, and two attendant behaviors of bipolar resistive switching and negative differential resistance appear after applying a magnetic field. The ideality factor (n) increases from 3.0 to 8.8 and the density of interface state Nss increases from 8.4×1013 to 1.8×1014 eV-1·cm-2 after applying a magnetic field. The variance of interface state density can be used to qualitatively understand the above results.

  16. Improved multiferroic properties of La-doped 0.6BiFeO3-0.4SrTiO3 solid solution ceramics

    Institute of Scientific and Technical Information of China (English)

    Ma Zheng-Zheng; Li Jian-Qing; Tian Zhao-Ming; Qiu Yang; Yuan Song-Liu

    2012-01-01

    The 0.6(Bi1-xLax)FeO3-0.4SrTiO3 (x =0,0.1) multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO3 and La in BiFeO3.The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure. The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO3 and substitution of La.The values of the dielectric constant εr and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature.The La-doped 0.6BiFeO3-0.4SrTiO3 ceramics exhibit improved dielectric and ferroelectric properties,with higher dielectric constant enhanced remnant polarization (Pr) and lower leakage current at room temperature.Compared with a anti-ferromagnetic BiFeO3 compound,the 0.6(Bi0.9La0.1)FeO3-0.4SrTiO3 sample shows the optimal ferromagnetism with remnant magnetization Mr ~ 0.135 emμ/g and ferroelectricity with Pr ~ 5.94 μC/cm2 at room temperature.

  17. Structure and optical properties of pure and Eu3+ doped SrTiO3 by the polymeric precursor and hydrothermal method

    Energy Technology Data Exchange (ETDEWEB)

    Silva, M.G.N.; Gasparotto, G.; Cebim, M. A.; Zaghete, M.A.; Varela, J.A. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Araraquara, SP (Brazil). Instituto de Quimica

    2009-07-01

    Full text: SrTiO3 (ST) has a simple cubic perovskite structure and is a semiconductor with an indirect band gap usually ranging from 3.2 to 3.4 eV. By modifying ST structurally, this material can be made to show a variety of physical properties. In this work, we report the preparation and characterization of pure and europium(III)-doped SrTiO3 obtained via the polymeric precursor and hydrothermal method. Samples were prepared containing different quantities of Eu3{sup +} ions in order to evaluate their effect on the structure property of the material. The analysis of X-ray diffraction results indicated that it was possible to obtain the SrTiO3 phase at 190 deg C free of secondary phases. We have also analyzed the powders by diffuse reflectance spectroscopy and evaluated the bandgap of the compounds using the Kubelka-Munk approximation. (author)

  18. 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.

  19. 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

  20. Chemistry, growth kinetics, and epitaxial stabilization of Sn2+ in Sn-doped SrTiO3 using (CH36Sn2 tin precursor

    Directory of Open Access Journals (Sweden)

    Tianqi Wang

    2016-12-01

    Full Text Available PbTiO3-based ferroelectrics have impressive electroactive properties, originating from the Pb2+ 6s2 electron lone-pair, which cause large elastic distortion and electric polarization due to cooperative pseudo Jahn-Teller effect. Recently, tin-based perovskite oxide (SnTiO3 containing Sn2+ and a chemistry similar to that of the 6s2 lone-pair has been identified as a thermally stable, environmentally friendly substitute for PbTiO3-based ferroelectrics. However experimental attempts to stabilize Sn2+ on the A-site of perovskite ATiO3 have so far failed. In this work, we report on the growth of atomically smooth, epitaxial, and coherent Sn-alloyed SrTiO3 films on SrTiO3 (001 substrates using a hybrid molecular beam epitaxy approach. With increasing Sn concentration, the out-of-plane lattice parameter first increases in accordance with the Vegard’s law and then decreases for Sn(Sr+Ti+Sn at. % ratio > 0.1 due to the incorporation of Sn2+ at the A-site. Using a combination of high-resolution X-ray photoelectron spectroscopy and density functional calculations, we show that while majority of Sn is on the B-site, there is a quantitatively unknown fraction of Sn being consistent with the A-site occupancy making SrTiO3 polar. A relaxor-like ferroelectric local distortion with monoclinic symmetry, induced by A-site Sn2+, was observed in Sn-doped SrTiO3 with Sn(Sr+Ti+Sn at. % ratio = 0.1 using optical second harmonic generation measurements. The role of growth kinetics on the stability of Sn2+ in SrTiO3 is discussed.

  1. Chemistry, growth kinetics, and epitaxial stabilization of Sn2+ in Sn-doped SrTiO3 using (CH3)6Sn2 tin precursor

    Science.gov (United States)

    Wang, Tianqi; Pitike, Krishna Chaitanya; Yuan, Yakun; Nakhmanson, Serge M.; Gopalan, Venkatraman; Jalan, Bharat

    2016-12-01

    PbTiO3-based ferroelectrics have impressive electroactive properties, originating from the Pb2+ 6s2 electron lone-pair, which cause large elastic distortion and electric polarization due to cooperative pseudo Jahn-Teller effect. Recently, tin-based perovskite oxide (SnTiO3) containing Sn2+ and a chemistry similar to that of the 6s2 lone-pair has been identified as a thermally stable, environmentally friendly substitute for PbTiO3-based ferroelectrics. However experimental attempts to stabilize Sn2+ on the A-site of perovskite ATiO3 have so far failed. In this work, we report on the growth of atomically smooth, epitaxial, and coherent Sn-alloyed SrTiO3 films on SrTiO3 (001) substrates using a hybrid molecular beam epitaxy approach. With increasing Sn concentration, the out-of-plane lattice parameter first increases in accordance with the Vegard's law and then decreases for Sn(Sr+Ti+Sn/) at. % ratio > 0.1 due to the incorporation of Sn2+ at the A-site. Using a combination of high-resolution X-ray photoelectron spectroscopy and density functional calculations, we show that while majority of Sn is on the B-site, there is a quantitatively unknown fraction of Sn being consistent with the A-site occupancy making SrTiO3 polar. A relaxor-like ferroelectric local distortion with monoclinic symmetry, induced by A-site Sn2+, was observed in Sn-doped SrTiO3 with Sn(Sr+Ti+Sn/) at. % ratio = 0.1 using optical second harmonic generation measurements. The role of growth kinetics on the stability of Sn2+ in SrTiO3 is discussed.

  2. Intrinsic Spin-Orbit Coupling in Superconducting Delta-Doped SrTiO3 Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Bell, Christopher

    2011-08-19

    We report the violation of the Pauli limit due to intrinsic spin-orbit coupling in SrTiO{sub 3} heterostructures. Via selective doping down to a few nanometers, a two-dimensional superconductor is formed, geometrically suppressing orbital pair-breaking. The spin-orbit scattering is exposed by the robust in-plane superconducting upper critical field, exceeding the Pauli limit by a factor of 4. Transport scattering times several orders of magnitude higher than for conventional thin film superconductors enables a new regime to be entered, where spin-orbit coupling effects arise non-perturbatively.

  3. Two-dimensional electron gas generated by La-doping at SrTiO3(001 surface: A first-principles study

    Directory of Open Access Journals (Sweden)

    Yun Li

    2013-06-01

    Full Text Available We carried out first-principles calculations to study the electronic properties of SrO-terminated and TiO2-terminated SrTiO3(001 surfaces with La-doping at the surface. We find that an intrinsic lower-lying state at the SrO-terminated surface can accommodate a two-dimensional electron gas (2DEG. By introducing La-doping at the SrO-terminated surface the energy position of the surface state and the 2DEG density can be tuned by changing the doping concentration. The higher the La-doping concentration, the lower the lower-lying state and the higher the 2DEG density. This 2DEG has a small effective mass and hopefully shows a high mobility.

  4. 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.

  5. The third-order optical nonlinearity of the stainless steel doped SrTiO3 thin film grown by L-MBE

    Institute of Scientific and Technical Information of China (English)

    Lifeng Liu(刘丽峰); Yiyan Fei(费义艳); Haizhong Guo(郭海中); Wenfeng Xiang(相文峰); Huibin Lü(吕惠宾); Zhenghao Chen(陈正豪)

    2003-01-01

    Stainless steel-doped SrTiO3 thin films were fabricated by laser molecular beam epitaxy (L-MBE).Nonlinear optical property of the thin film was measured by the single beam Z-scan technique at thewavelength of 532 nm. Two two-phonon absorption coefficient and nonlinear refractive index weredetermined to be 9.37 × 10-7 m/W and 1.55 × 10-6 esu, respectively. The merit figure T was calculatedto be 1.8, satisfying condition T < 2 for an optical switch. The thin film has a very promising prospectfor the applications in optical device.

  6. 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.

  7. 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.

  8. Signature of enhanced spin-orbit interaction in the magnetoresistance of LaTiO3/SrTiO3 interfaces on δ doping

    Science.gov (United States)

    Das, Shubhankar; Hossain, Z.; Budhani, R. C.

    2016-09-01

    We present a study of modulation of spin-orbit interaction (SOI) at the interface of LaTiO3/SrTiO3 by δ doping with an isostructural ferromagnetic perovskite LaCoO3. The sheet carrier density at the interface decreases exponentially with δ -doping thickness. We have explored that the spin-orbit scattering time (τs o) can be decreased by nearly three orders of magnitude, whereas the inelastic scattering time (τi) remains almost constant with δ -doping thickness. We have also observed that the τi varies almost inversely proportional to temperature and τs o remains insensitive to temperature, which suggest that the spin relaxation in these interfaces follows D'yakonov-Perel mechanism. The observed in-plane anisotropic magnetoresistance is attributed to the mixing of the spin-up and spin-down states of the d band at the Fermi level due to SOI.

  9. 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).

  10. Improvement of visible light-induced photocatalytic performance by Cr-doped SrTiO3-carbon nitride intercalation compound (CNIC) composite

    Institute of Scientific and Technical Information of China (English)

    杨明; 金效齐

    2016-01-01

    Novel organic−inorganic composite photocatalyst offers new opportunities in the practical applications of photocatalysis. Novel visible light-induced Cr-doped SrTiO3–carbon nitride intercalation compound (CNIC) composite photocatalysts were synthesized. The composite photocatalyst was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR) spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence (PL) spectroscopy, and BET surface area analyzer. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl orange (MO) as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO. For maximizing the photodegradation activity of the composite photocatalysts, the optimal CNIC content was determined. The improved photocatalytic activity of the as-prepared Cr-doped SrTiO3–CNIC composite photocatalyst may be attributed to the enhancement of photo-generated electron–hole separations at the interface.

  11. AC Electrical Conduction of Cr-Doped SrTiO3 Thin Films with an Oxygen-Deficient Interface Layer

    Science.gov (United States)

    Phan, Bach Thang; Eom, Ki Tae; Lee, Jaichan

    2017-06-01

    The ac electrical conduction of Cr-doped SrTiO3 thin films with an oxygen-deficient interface layer was investigated as a function of temperature and frequency. The Cr-doped SrTiO3 (Cr-STO) thin films with an ultra-thin (˜2 nm) oxygen-deficient layer inserted between the top electrode and the Cr-STO layer exhibited two ac conduction mechanisms, i.e., variable-range hopping and small-polaron hopping conduction, accompanied by a relaxation process. Since high oxygen deficiency induces large lattice distortion in the depletion layer, the first relaxation process occurs at low frequencies in the thin oxygen depletion layer Cr-SrTiO3- δ , and the corresponding conduction behavior follows the small-polaron tunneling model. In the high frequency range, an additional relaxation process is involved and is associated with the variable-range hopping between the localized states in the band gap of the thick Cr-SrTiO3 layer.

  12. Selective Inactivation of Bacteriophage in the Presence of Bacteria by Use of Ground Rh-Doped SrTiO3 Photocatalyst and Visible Light.

    Science.gov (United States)

    Yamaguchi, Yuichi; Usuki, Sho; Kanai, Yoshihiro; Yamatoya, Kenji; Suzuki, Norihiro; Katsumata, Ken-Ichi; Terashima, Chiaki; Suzuki, Tomonori; Fujishima, Akira; Sakai, Hideki; Kudo, Akihiko; Nakata, Kazuya

    2017-09-20

    Bacteriophage (denoted as phage) infection in the bacterial fermentation industry is a major problem, leading to the loss of fermented products such as alcohol and lactic acid. Currently, the prevention of phage infection is limited to biological approaches, which are difficult to apply in an industrial setting. Herein, we report an alternative chemical approach using ground Rh-doped SrTiO3 (denoted as g-STO:Rh) as a visible-light-driven photocatalyst. The g-STO:Rh showed selective inactivation of phage without bactericidal activity when irradiated with visible light (λ > 440 nm). After inactivation, the color of g-STO:Rh changed from gray to purple, suggesting that the Rh valence state partially changed from 3+ to 4+ induced by photocatalysis, as confirmed by diffuse reflectance spectroscopy. To study the effect of the Rh(4+) ion on phage inactivation under visible-light irradiation, the survival rate of phage for g-STO:Rh was compared to that for ground Rh,Sb-codoped SrTiO3 (denoted as g-STO:Rh,Sb), where the change of Rh valence state from 3+ to 4+ is almost suppressed under visible-light irradiation due to charge compensation by the Sb(5+) ion. Only g-STO:Rh effectively inactivated phage, which indicated that Rh(4+) ion induced by photocatalysis particularly contributed to phage inactivation under visible-light irradiation. These results suggested that g-STO:Rh has potential as an antiphage material in bacterial fermentation.

  13. Visible Light-induced Cr-doped SrTiO3-g-C3N4 Composite for Improved Photocatalytic Performance

    Institute of Scientific and Technical Information of China (English)

    YANG Ming; JIN Xiaoqi

    2014-01-01

    Novel visible light-induced Cr-doped SrTiO3-g-C3N4 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The composite photocatalyst was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR) spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence (PL) spectroscopy and BET surface area measurements. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl orange (MO) as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO. The optimal g-C3N4 content for the photodegradation activity of the composite photocatalysts was determined. The as-prepared composite photocatalyst exhibits an improved photocatalytic activity due to enhancement of photo-generated electron-hole separation at the interface.

  14. Promoting oxygen vacancy formation and p-type conductivity in SrTiO3via alkali metal doping: a first principles study.

    Science.gov (United States)

    Triggiani, Leonardo; Muñoz-García, Ana B; Agostiano, Angela; Pavone, Michele

    2016-10-19

    Strontium titanate (SrTiO3, STO) is a prototypical perovskite oxide, widely exploited in many technological applications, from catalysis to energy conversion devices. In the context of solid-oxide fuel cells, STO has been recently applied as an epitaxial substrate for nano-sized layers of mixed ion-electron conductive catalysts with enhanced electrochemical performances. To extend the applications of such heterogeneous nano-cathodes in real devices, also the STO support should be active for both electron transport and oxide diffusion. To this end, we explored using first-principles calculations the strategy of doping of STO at the Sr site with sodium and potassium. These two ions fit in the perovskite structure and induce holes in the STO valence band, so as to obtain the desired p-type electronic conduction. At the same time, the doping with alkali ions also promotes the formation of oxygen vacancies in STO, a prerequisite for effective oxide diffusion. Analysis of electron density rearrangements upon defect formation allows relating the favorable vacancy formation energies to an improved electronic delocalization over the oxide sub-lattice, as observed in closely related materials (e.g. Sr2Fe1.5Mo0.5O6). Overall, our results suggest the alkali-doped STO as a new potential substrate material in nanoscale heterogeneous electrodes for solid oxide electrochemical cells.

  15. Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3.

    Science.gov (United States)

    Ge, Jian-Feng; Liu, Zhi-Long; Liu, Canhua; Gao, Chun-Lei; Qian, Dong; Xue, Qi-Kun; Liu, Ying; Jia, Jin-Feng

    2015-03-01

    Recent experiments on FeSe films grown on SrTiO3 (STO) suggest that interface effects can be used as a means to reach superconducting critical temperatures (Tc) of up to 80 K (ref. ). This is nearly ten times the Tc of bulk FeSe and higher than the record value of 56 K for known bulk Fe-based superconductors. Together with recent studies of superconductivity at oxide heterostructure interfaces, these results rekindle the long-standing idea that electron pairing at interfaces between two different materials can be tailored to achieve high-temperature superconductivity. Subsequent angle-resolved photoemission spectroscopy measurements of the FeSe/STO system revealed an electronic structure distinct from bulk FeSe (refs , ), with an energy gap vanishing at around 65 K. However, ex situ electrical transport measurements have so far detected zero resistance-the key experimental signature of superconductivity-only below 30 K. Here, we report the observation of superconductivity with Tc above 100 K in the FeSe/STO system by means of in situ four-point probe electrical transport measurements. This finding confirms FeSe/STO as an ideal material for studying high-Tc superconductivity.

  16. Modulated two-dimensional charge-carrier density in LaTiO3-layer-doped LaAlO3/SrTiO3 heterostructure.

    Science.gov (United States)

    Nazir, Safdar; Bernal, Camille; Yang, Kesong

    2015-03-11

    The highly mobile two-dimensional electron gas (2DEG) formed at the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) is a matter of great interest because of its potential applications in nanoscale solid-state devices. To realize practical implementation of the 2DEG in device design, desired physical properties such as tuned charge carrier density and mobility are necessary. In this regard, polar perovskite-based transition metal oxides can act as doping layers at the interface and are expected to tune the electronic properties of 2DEG of STO-based HS systems dramatically. Herein, we investigated the doping effects of LaTiO3(LTO) layers on the electronic properties of 2DEG at n-type (LaO)(+1)/(TiO2)(0) interface in the LAO/STO HS using spin-polarized density functional theory calculations. Our results indicate an enhancement of orbital occupation near the Fermi energy, which increases with respect to the number of LTO unit cells, resulting in a higher charge carrier density of 2DEG than that of undoped system. The enhanced charge carrier density is attributed to an extra electron introduced by the Ti 3d(1) orbitals from the LTO dopant unit cells. This conclusion is consistent with the recent experimental findings (Appl. Phys. Lett. 2013, 102, 091601). Detailed charge density and partial density of states analysis suggests that the 2DEG in the LTO-doped HS systems primarily comes from partially occupied dyz and dxz orbitals.

  17. 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.

  18. Investigation of Electric Field–Induced Structural Changes at Fe-Doped SrTiO3 Anode Interfaces by Second Harmonic Generation

    Directory of Open Access Journals (Sweden)

    David Ascienzo

    2016-10-01

    Full Text Available We report on the detection of electric field–induced second harmonic generation (EFISHG from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage increases. The enhancements are attributed to a field-stabilized electrostriction, leading to Fe:Ti-O bond stretching and bending in Fe:Ti-O6 octahedra. For the oxidized crystal, no obvious structural changes are observed below 16 kV/cm. Above 16 kV/cm, a sharp enhancement of the susceptibilities occurs due to local electrostrictive deformations in response to oxygen vacancy migrations away from the anode. Differences between the reduced and oxidized crystals are explained by their relative oxygen vacancy and free carrier concentrations which alter internal electric fields present at the Pt/Fe:STO interfaces. Our results show that the optical SHG technique is a powerful tool for detecting structural changes near perovskite-based oxide interfaces due to field-driven oxygen vacancy migration.

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

    Energy Technology Data Exchange (ETDEWEB)

    Meevasana, Warawat

    2010-05-26

    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{sub 3} (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La{sub 2}CuO{sub 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{sub 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 {lambda}{prime} {approx} 0.3 and an overall bandwidth renormalization suggesting an overall {lambda}{prime} {approx} 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.

  20. Large linear magnetoresistance in heavily-doped Nb:SrTiO3 epitaxial thin films

    Science.gov (United States)

    Jin, Hyunwoo; Lee, Keundong; Baek, Seung-Hyub; Kim, Jin-Sang; Cheong, Byung-Ki; Park, Bae Ho; Yoon, Sungwon; Suh, B. J.; Kim, Changyoung; Seo, S. S. A.; Lee, Suyoun

    2016-10-01

    Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin films. These phenomena are associated with the interplay between the large classical MR due to high carrier mobility and the electronic localization effect due to strong spin-orbit coupling, implying that heavily Nb-doped Sr(Nb0.2Ti0.8)O3 is promising for the application in spintronic devices.

  1. Temperature-dependent photovoltage response in La0.9Li0.1MnO3/SrTiO3-Nb heterojunction induced by a low intensity pulse laser

    Science.gov (United States)

    Wang, Jianyuan; Bai, Jianying; Xing, Hui; Wang, Shuanhu; Wang, Min; Jin, Kexin; Chen, Changle

    2017-02-01

    The photovoltage response under low intensity pulse laser (473 nm) in the perovskite manganite p-n junction La0.9Li0.1MnO3/SrTiO3:Nb is investigated within a wide temperature range. The maximum photovoltage occurs at around the metal-insulator transition temperature (TMI, 250 K) of La0.9Li0.1MnO3 rather than the lowest temperature, which indicates that the low density charge induced by a weak light can be significantly affected by the leakage rather than the thermal carriers. Moreover, the time response of photovoltage shows distinct temperature-dependent and light intensity-dependent regularities in the temperature regions TTMI respectively. The mechanisms are discussed according to the charge transport and magnetic phase transition of La0.9Li0.1MnO3.

  2. Low Temperature Specific Heat in Lightly Mn-Substituted Electron-Doped SrTiO3

    Science.gov (United States)

    Okuda, Tetsuji; Hata, Hiroto; Eto, Takahiro; Sobaru, Shogo; Oda, Ryosuke; Noda, Masaaki; Kuwahara, Hideki

    2017-08-01

    We found large changes in the low-temperature specific heat (low-T C) in the lightly Mn-substituted electron-doped perovskites Sr0.95La0.05Ti1-yMnzO3 with y = 0.02 and 0.04 by applying magnetic fields up to 9 T. The changes in the low-T C are qualitatively well explained by the Schottky specific heat (CSch) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. However, the actual numbers of localized spins estimated from CSch are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons.

  3. 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.

  4. Atomic Resolution Interfacial Structure of Lead-free Ferroelectric K0.5Na0.5NbO3 Thin films Deposited on SrTiO3.

    Science.gov (United States)

    Li, Chao; Wang, Lingyan; Wang, Zhao; Yang, Yaodong; Ren, Wei; Yang, Guang

    2016-11-25

    Oxide interface engineering has attracted considerable attention since the discovery of its exotic properties induced by lattice strain, dislocation and composition change at the interface. In this paper, the atomic resolution structure and composition of the interface between the lead-free piezoelectric (K0.5Na0.5)NbO3 (KNN) thin films and single-crystalline SrTiO3 substrate were investigated by means of scanning transmission electron microscopy (STEM) combining with electron energy loss spectroscopy (EELS). A sharp epitaxial interface was observed to be a monolayer composed of Nb and Ti cations with a ratio of 3/1. The First-Principles Calculations indicated the interface monolayer showed different electronic structure and played the vital role in the asymmetric charge distribution of KNN thin films near the interface. We also observed the gradual relaxation process for the relatively large lattice strains near the KNN/STO interface, which remarks a good structure modulation behavior of KNN thin films via strain engineering.

  5. Atomic Resolution Interfacial Structure of Lead-free Ferroelectric K0.5Na0.5NbO3 Thin films Deposited on SrTiO3

    Science.gov (United States)

    Li, Chao; Wang, Lingyan; Wang, Zhao; Yang, Yaodong; Ren, Wei; Yang, Guang

    2016-11-01

    Oxide interface engineering has attracted considerable attention since the discovery of its exotic properties induced by lattice strain, dislocation and composition change at the interface. In this paper, the atomic resolution structure and composition of the interface between the lead-free piezoelectric (K0.5Na0.5)NbO3 (KNN) thin films and single-crystalline SrTiO3 substrate were investigated by means of scanning transmission electron microscopy (STEM) combining with electron energy loss spectroscopy (EELS). A sharp epitaxial interface was observed to be a monolayer composed of Nb and Ti cations with a ratio of 3/1. The First-Principles Calculations indicated the interface monolayer showed different electronic structure and played the vital role in the asymmetric charge distribution of KNN thin films near the interface. We also observed the gradual relaxation process for the relatively large lattice strains near the KNN/STO interface, which remarks a good structure modulation behavior of KNN thin films via strain engineering.

  6. First-principles calculations on electronic structures of B-doped SrTiO3%B掺杂SrTiO 3电子结构的第一性原理计算

    Institute of Scientific and Technical Information of China (English)

    刘晨吉; 贾云龙; 刘红; 吴一; 刘磊; 郑树凯

    2016-01-01

    利用基于密度泛函理论(DFT)的第一性原理平面波超软赝势法,对未掺杂、B替位Sr、B替位Ti、B替位O和B间隙掺杂SrTiO 3的晶格参数、Mulliken电荷布居、能带结构、态密度和光吸收系数进行计算。结果表明:B替位Sr和B替位Ti掺杂对SrTiO3电子结构和光学性质的影响不显著;B替位O掺杂则在SrTiO3的禁带中引入3条杂质能级,杂质能级上的电子可以吸收能量较小的光子跃迁至导带,光吸收强度从可见光长波段550 nm开始逐渐增加,光谱吸收边红移;B以间隙原子的形式掺杂时,SrTiO 3的禁带宽度大幅增大,电子跃迁能增加,光谱吸收边蓝移。%The lattice parameters, Mulliken charge populations, energy band structures, density of states and absorption coefficients of pure SrTiO3, B substitutes for Sr or Ti, and interstitial B doped SrTiO3 were studied by the first-principles plane wave ultra-soft pseudo-potential method based on the density functional theory (DFT). The results show that the impacts on the electronic structures and optical properties of SrTiO3 are not significant when the B atom substitutes for the Sr or Ti atom. When B substitutes for O atom, three impurity levels are introduced into the band gap of SrTiO3, the electrons on the impurity levels can transit to the conduction band by absorbing photon of less energy, the intensity of light absorption begins to increase gradually from visible light wavelength of 550 nm and the spectral absorption edge has a red shift. When B is in the form of interstitial, the width of forbidden band of SrTiO3 enlarges significantly and the transition energy of the electrons increases, which results in the blue shift of the spectral absorption edge.

  7. Aspects of the SrO-CuO-TiO2 Ternary System Related to the Deposition of SrTiO3 and Copper-Doped SrTiO3 Thin-Film Buffer Layers

    Energy Technology Data Exchange (ETDEWEB)

    A. Ayala

    2004-12-20

    YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) coated conductors are promising materials for large-scale superconductivity applications. One version of a YBCO coated conductor is based on ion beam assisted deposition (IBAD) of magnesium oxide (MgO) onto polycrystalline metal substrates. SrTiO{sub 3} (STO) is often deposited by physical vapor deposition (PVD) methods as a buffer layer between the YBCO and IBAD MgO due to its chemical stability and lattice mismatch of only {approx}1.5% with YBCO. In this work, some aspects of the stability of STO with respect to copper (Cu) and chemical solution deposition of STO on IBAD MgO templates were examined. Solubility limits of Cu in STO were established by processing Cu-doped STO powders by conventional bulk preparation techniques. The maximum solubility of Cu in STO was {approx}1% as determined by transmission electron microscopy (TEM) and Rietveld refinements of x-ray diffraction (XRD) data. XRD analysis, performed in collaboration with NIST, on powder compositions on the STO/SrCuO{sub 2} tie line did not identify any ternary phases. SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer layers were prepared by pulsed laser deposition (PLD) and CSD on IBAD MgO flexible metallic textured tapes. TEM analysis of a {approx}100 nm thick SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. A {approx}600 nm thick YBCO film, deposited onto the SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer by PLD, exhibited a T{sub c} of 87 K and critical current density (J{sub c}) of {approx}1 MA/cm{sup 2}. STO and Cu-doped STO thin films by CSD were {approx}30 nm thick. The in plane alignment (FWHM) after deposition of the STO improved by {approx}1{sup o} while it degraded by {approx}2{sup o} with the SrCu{sub 0.05}TiO{sub y} buffer. YBCO was deposited by PLD on the STO and SrCu{sub 0.05}TiO{sub y} buffers. The in plane alignment (FWHM) of the YBCO with the STO buffer layer slightly improved while that of the

  8. The influence of doped Mg2+ SrTiO3 film photoelectric properties%Mg2+掺杂对SrTiO3薄膜光电特性的影响

    Institute of Scientific and Technical Information of China (English)

    刘雪婷; 何崇斌; 薛异荣; 焦龙龙

    2013-01-01

    The different content of Mg ion doping SrTiO3 thin film ceramic wafer was prepared by sol-gel on the Al2 O3,Mg in SrTiO3 replace titanium,forming an acceptor doping.This paper studied the influence of different content doping on the film's resistively,show that,when the doping concentration was 4%,resistively minimum.Also studied doping concentration was 4%,film resistively with the optical power change,show that,when the light power was less than 100W,resistively decreases rapidly,more than 100W,reduced smaller amplitude.%利用溶胶-凝胶法在Al2O3陶瓷片上制备掺Mg的SrTiO3薄膜.在SrTiO3中掺杂不同含量的Mg离子,Mg在钛酸锶中取代钛位,形成受主掺杂.研究了掺杂对薄膜电阻率的影响,实验表明,当掺杂浓度为4%时,电阻率最小.当掺杂浓度为4%时,薄膜电阻率会随着光功率变化而变化,当光功率<100W时,电阻迅速减小,超过100W时,减小幅度变小.

  9. Effect of fabrication conditions on phase formation and properties of epitaxial (PbMg1/3Nb2/3O3)0.67-(PbTiO3)0.33 thin films on (001) SrTiO3

    NARCIS (Netherlands)

    Boota, M.; Houwman, E.P.; Nguyen, M.D.; Lanzara, G.; Rijnders, A.J.H.M.

    2016-01-01

    The pulsed laser deposition process of 300nm thick films of Pb(Mg1/3Nb2/3)O3)0.67-(PbTiO3)0.33 on (001)-oriented SrTiO3 was studied by varying deposition pressure, substrate deposition temperature, laser fluence on the target and target-substrate distance. Perovskite phase pure, (001)-oriented, epit

  10. Origin of Charge Density at LaAlO3 on SrTiO3 Heterointerfaces: Possibility of Intrinsic Doping

    Science.gov (United States)

    Siemons, Wolter; Koster, Gertjan; Yamamoto, Hideki; Harrison, Walter A.; Lucovsky, Gerald; Geballe, Theodore H.; Blank, Dave H. A.; Beasley, Malcolm R.

    2007-05-01

    As discovered by Ohtomo and Hwang, a large sheet charge density with high mobility exists at the interface between SrTiO3 and LaAlO3. Based on transport, spectroscopic, and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also present a model that explains the high mobility based on carrier redistribution due to an increased dielectric constant.

  11. Characterization of SrTiO3 target doped with Co ions, SrCoxTi1-xO3-δ, and their thin films prepared by pulsed laser ablation (PLA) in water for visible light response

    Science.gov (United States)

    Ichihara, Fumihiko; Murata, Yuma; Ono, Hiroshi; Choo, Cheow-keong; Tanaka, Katsumi

    2017-10-01

    SrTiO3 (STO) and Co-doped SrTiO3 (Co-STO) sintered targets were synthesized and were Ar+ sputtered to elucidate the charge compensation effect between Sr, Ti and Co cations following the reduction by oxygen desorption. Following exposure of the Ar+-sputtered target to the air, charge transfer reactions occurred among Co2+, Ti3+, O2- and Sr2+ species which were studied by their XPS spectra. Pulsed laser ablation (PLA) of these targets was carried out in water to prepare the nanoparticles which could be supplied to the thin films with much higher surface reactivity expected for photocatalytic reactions. The roles of Co ions were studied for the stoichiometry and crystallinity of the nanoparticles which constituted the thin films. Photo-degradation of methylene blue was carried out on the PLA thin films under very weak visible light at 460 nm. The PLA thin films showed the photocatalytic activities, which were enhanced by the presence of Co ions. Such the effect of Co ions was considered from viewpoint of the d-d transition and the charge-transfer between Co ions and the ligand oxygen.

  12. Synergetic pinning centres in BaZrO3-doped YBa2Cu3O7-x films induced by SrTiO3 nano-layers

    Science.gov (United States)

    Crisan, A.; Dang, V. S.; Mikheenko, P.; Ionescu, A. M.; Ivan, I.; Miu, L.

    2017-04-01

    We report on the enhancement of critical current density (J c) and the unusual behaviour of its dependence on field orientation in YBa2Cu3O7‑x (YBCO) nanostructured films by a combination of substrate decoration with Ag nano-dots, of the incorporation of BaZrO3 (BZO) nano-particles and nano-rods, and of multilayer architecture (a thin SrTiO3 layer separating two 1.5 μm-thick YBCO layers). SrTiO3 insulating layers were 15, 30 or 45 nm thick. The highest improvement of J c in applied magnetic fields along the c-axis and smaller than 1 T occurs in the bi-layer with 30 nm-thick STO, but the influence of STO thickness is small. Our thick nanostructured films show significant improvement of J c in the magnetic field along the ab-plane direction. The presence of BZO nano-rods, ab-plane defects and nano particles of BZO and Y2O3 was observed in transmission electron microscopy (TEM) images of the film. The peculiarities of artificial pinning centres revealed in the TEM images of the nanostructured films are used to explain an unusual split of the peak in the J c dependence on the magnetic field along the ab-plane of YBCO. Effective pinning potentials in high magnetic fields have rather high values for such thick films.

  13. Influence of structural evolution on energy storage properties in Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics

    Science.gov (United States)

    Li, Feng; Zhai, Jiwei; Shen, Bo; Liu, Xing; Yang, Ke; Zhang, Yang; Li, Peng; Liu, Baihui; Zeng, Huarong

    2017-02-01

    Lead-free (1-x)(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-xNaNbO3 (x = 0-0.1, abbreviated as BNT-ST-xNN) ceramics were fabricated by a conventional sintering route with pure perovskite phase via XRD analysis. Raman spectrum was exploited in order to give an insight into the variation of local structural evolution. All compositions exhibited an obvious evolution of dielectric relaxation behaviors. Dielectric and ferroelectric properties clarified that a crossover from nonergodic to ergodic relaxor properties was obtained with the addition of NN content. A relatively large energy storage density was obtained WRec ˜ 0.74 J/cm3 at 7 kV/mm for x = 0.05 at room temperature. Particularly, the energy storage properties exhibited temperature (25-160 °C) and frequency stability (0.1-20 Hz) with WRec around 0.6 J/cm3 at 6 kV/mm for x = 0.05 within the ergodic region. Pulsed discharging current waveforms were measured under different electric fields to detect the energy storage density and discharging speed behavior. An illustration of the charge-discharge process for the nonergodic and ergodic relaxor was depicted in order to disclose the difference of energy storage properties in BNT-ST-xNN system, and it is believed that this concept can be a guideline for fixing a position when designing a new energy-storage system for BNT-based relaxor ferroelectric ceramics.

  14. Superconductivity versus bound-state formation in a two-band superconductor with small Fermi energy: Applications to Fe pnictides/chalcogenides and doped SrTiO3

    Science.gov (United States)

    Chubukov, Andrey V.; Eremin, Ilya; Efremov, Dmitri V.

    2016-05-01

    Fe pnictides and Fe chalcogenides in which a superconducting gap has been detected on the bands that do not cross the Fermi level, and to FeSe, in which the superconducting gap is comparable to the Fermi energy. We apply the results for the model with two electron bands to Nb-doped SrTiO3 and argue that our theory explains the rapid increase of Tc when both bands start crossing the Fermi level.

  15. Ordered SrTiO3 Nanoripples Induced by Fo cused Ion Beam

    Institute of Scientific and Technical Information of China (English)

    Jiang Wu; Gang Chen; Zhaoquan Zeng; Shibin Li; Xingliang Xu; Zhiming M Wang; Gregory J Salamo

    2012-01-01

    Ordered nanoripples on the niobium-doped SrTiO3 surfaces were fabricated through focused ion beam bombardment. The surface morphology of the SrTiO3 nanoripples was characterized using in situ focused ion beam/scanning electron microscopy. The well-aligned SrTiO3 nanostructures were obtained under optimized ion irradiation conditions. The characteristic wavelength was measured as about 210 nm for different ion beam currents. The relationship between the ion irradiation time and current and SrTiO3 surface morphology was analyzed. The presented method will be an effective supplement for fabrication of SrTiO3 nanostructures that can be used for ferroelectric and electronic applications.

  16. Large phonon-drag enhancement induced by narrow quantum confinement at the LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Pallecchi, I.; Telesio, F.; Marré, D.; Li, D.; Gariglio, S.; Triscone, J.-M.; Filippetti, A.

    2016-05-01

    The thermoelectric power of the two-dimensional electron system (2DES) at the LaAlO3/SrTiO3 interface is explored below room temperature, in comparison with that of Nb-doped SrTiO3 single crystals. For the interface, we find a region below T =50 K where thermopower is dominated by phonon drag, whose amplitude is hugely amplified with respect to the corresponding bulk value, reaching values ˜mV /K and above. The phonon-drag enhancement at the interface is traced back to the tight carrier confinement of the 2DES, and represents a sharp signature of strong electron-acoustic phonon coupling at the interface.

  17. Co掺杂钙钛矿SrTiO3磁性机理的理论研究%Theoretical Study on the Magnetic Mechanism of Co-doped Perovskite SrTiO3

    Institute of Scientific and Technical Information of China (English)

    王青; 李强; 戴剑锋; 郭永庆; 张仁辉

    2011-01-01

    采用第一性原理LDA+U方法研究了Co掺杂SrTiO3的磁性机理,对不同掺杂体系的基态能量、电子结构、态密度、居里温度及缺陷替位能进行了计算分析.结果表明,无氧空位的掺杂体系呈现出反铁磁性或顺磁性,而有氧空位掺杂体系却表现出铁磁性;掺杂体系的晶胞磁矩主要来自于Co离子局域磁矩的贡献;随着Co和氧空位浓度的增加,掺杂体系表现出室温铁磁性;Co离子和氧空位的共同作用降低了体系的缺陷替位能;掺杂体系中Co离子之间的铁磁性耦合可以用束缚磁极子机制解释.%The magnetic mechanism in Co-doped perovskite SrTiO3 with and without oxygenvacancies was investigated by first principles with LDA+U approach. Ground state energy, electronic structures, density of states, Curie temperature and substitution energy were investigated for various configurations. The calculated results imply that the species without oxygen vacancies exhibit antiferromagnetism or paramagnetism. The species with oxygen vacancies show strong ferromagnetism. Unit cell magnetic moment originates from local magnetic moment of Co ions. With the increasing concentration of Co ions, room-temperature ferromagnetism can be realized. The interaction between Co ions and oxygen vacanciea will lower the defect substitution energy of Co-doped SrTiO3. The ferromagnetic coupling between Co ions can be explained in the terms of the bound magnetic pelaron mechanism.

  18. Investigation of chemical compatibility between B-site doped La substituted SrTiO3 anode and stabilized zirconia electrolyte

    Science.gov (United States)

    Chen, Gang; Qian, Yu Min; Liu, Man; Ma, Wan Qing; Geng, Shu Jiang; Meng, Xiang Ying; Yu, Kai; Liu, Guo Qiang

    2016-10-01

    High temperature annealing test results indicate that B site dopant of LST and corresponding doping concentration have strong impact on the inter-diffusion behaviors at A-site deficient LST and ScSZ interface, which provides solid evidence for the improvement of the long term stability of LST anode. First principle calculation results indicate that B site doping of Al, Ga and Sc can enhance the neighboring Tisbnd O bonding which increases the VFE of Ti in LST that stabilizes the material and blocks the ion diffusion path at the same time. To minimize B site cation vacancy concentration, a threshold doping concentration exists at which the resulting VFE of Ti can overwhelm that of Sc which effectively suppresses the Sc/Ti ion exchange at the LST/ScSZ interface. But introduction of the B-site dopant may deteriorate the stability due to the lower VFE of dopant itself which becomes new source of instability at high doping concentration. Appropriate doping to balance the improvement and drawback of the dopant is the key for the overall stability of the material.

  19. Thermoelectric properties of n-type SrTiO3

    Directory of Open Access Journals (Sweden)

    Jifeng Sun

    2016-10-01

    Full Text Available We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

  20. Thermoelectric properties of n-type SrTiO3

    Science.gov (United States)

    Sun, Jifeng; Singh, David J.

    2016-10-01

    We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

  1. Influence of chromium concentration on the electron magnetic resonance linewidth of Cr3+ in SrTiO3

    Directory of Open Access Journals (Sweden)

    Ronaldo Sergio de Biasi

    2012-06-01

    Full Text Available Electron magnetic resonance (EMR spectra of Cr3+ ions in samples of chromium-doped strontium titanate (SrTiO3 have been studied at room temperature for chromium concentrations between 0.20 and 1.00 mol%. According to previous studies, chromium substitutes Ti4+ sites in the lattice and its preferred valence state is Cr4+, which is EMR silent in the X-band, but the trivalent state can be produced by illumination or codoping with Nb. In the present work, the codoping method was used; the results show the electron magnetic resonance linewidth of the Cr3+ spectrum increases with increasing chromium concentration and that the range of the exchange interaction between Cr3+ ions is about 0.96 nm.

  2. 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...

  3. The effect of Rhδ+ dopant in SrTiO3 on the active oxidation state of co-catalytic Pt nanoparticles in overall water splitting

    NARCIS (Netherlands)

    Zoontjes, M.G.C.; Han, K.; Huijben, M.; Wiel, van der W.G.; Mul, G.

    2016-01-01

    We report on the oxidation state of Pt nanoparticles when deposited on SrTiO3 or Rh-doped SrTiO3 under realistic solar water-splitting conditions. The oxidation state was investigated using state-of-the-art analysis of the reaction in a continuously stirred tank reactor (CSTR) connected to a micro g

  4. 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.

  5. Phonon mechanism in the most dilute superconductor n-type SrTiO3.

    Science.gov (United States)

    Gor'kov, Lev P

    2016-04-26

    Superconductivity of n-doped SrTiO3, which remained enigmatic for half a century, is treated as a particular case of nonadiabatic phonon pairing. Motivated by experiment, we suggest the existence of the mobility edge at some dopant concentration. The itinerant part of the spectrum consists of three conduction bands filling by electrons successively. Each subband contributes to the superconducting instability and exhibits a gap in its energy spectrum at low temperatures. We argue that superconductivity of n-doped SrTiO3 results from the interaction of electrons with several longitudinal (LO) optical phonons with frequencies much larger than the Fermi energy. Immobile charges under the mobility edge threshold increase the "optical" dielectric constant far above that in clean SrTiO3 placing control on the electron-LO phonon interaction. TC initially grows as density of states at the Fermi surface increases with doping, but the accumulating charges reduce the electrons-polar-phonon interaction by screening the longitudinal electric fields. The theory predicts maxima in the TC-concentration dependence indeed observed experimentally. Having reached a maximum in the third band, the transition temperature finally decreases, rounding out the TC (n) dome, the three maxima with accompanying superconducting gaps emerging consecutively as electrons fill successive bands. This arises from attributes of the LO optical phonon pairing of electrons. The mechanism of LO phonons opens the path to increasing superconducting transition temperature in bulk transition-metal oxides and other polar crystals, and in charged 2D layers at the LaAaO3/SrTiO3 interfaces and on the SrTiO3 substrates.

  6. Effect of fabrication conditions on phase formation and properties of epitaxial (PbMg1/3Nb2/3O30.67-(PbTiO30.33 thin films on (001 SrTiO3

    Directory of Open Access Journals (Sweden)

    Muhammad Boota

    2016-05-01

    Full Text Available The pulsed laser deposition process of 300nm thick films of Pb(Mg1/3Nb2/3O30.67-(PbTiO30.33 on (001-oriented SrTiO3 was studied by varying deposition pressure, substrate deposition temperature, laser fluence on the target and target-substrate distance. Perovskite phase pure, (001-oriented, epitaxial smooth films were obtained in a narrow range of deposition parameters. The ferroelectric and dielectric properties of films fabricated within this parameter range still vary significantly. This shows the sensitivity of the system for growth conditions. The best film has a polarization value close to that expected for a (001 poled, stress free single crystal film. All films show deposition conditions dependent variations in the self-bias field. The self-bias is very stable during long cycling for films made at optimum deposition conditions. The piezoelectric coefficients of the films are strongly reduced with respect to bulk single crystal values due to the film clamping. The properties variations are ascribed to changes in the grain boundary properties in which film defects are expected to accumulate. Notably slight off-stoichiometry may cause localized screening charges, affecting specifically the polarization and dielectric constant.

  7. Large strain response based on relaxor-antiferroelectric coherence in Bi0.5Na0.5TiO3-SrTiO3-(K0.5Na0.5)NbO3 solid solutions

    Science.gov (United States)

    Liu, Laijun; Shi, Danping; Knapp, Michael; Ehrenberg, Helmut; Fang, Liang; Chen, Jun

    2014-11-01

    The effect of (K0.5Na0.5)NbO3 (KNN) addition on the ferroelectric and dielectric behavior of 90Bi0.5Na0.5TiO3-10SrTiO3 (BNT-ST) lead-free piezoceramics was investigated. Polarization and strain hysteresis loops indicate that a relaxor-antiferroelectric coherence will be produced with the addition of KNN as a replacement for ST up to 5% and the destabilization of the phase coherence is accompanied by an enhancement of the bipolar strain with the increase of temperature, which is ˜0.37% (corresponding to a large signal d33* of ˜530 pm/V at 90 °C) at 5 mol. % KNN content. This strain was analyzed as derived from an electrostrictive effect at lower electric fields and a field-induced antiferroelectric-ferroelectric phase transition at higher electric fields. The large polar strain response would be of great interest for environmental friendly high-temperature actuators.

  8. Impedance and Stability of M/CGO (M: Ni, Pd, Ru) Co-infiltrated Nb-doped SrTiO3 SOFC Anodes

    DEFF Research Database (Denmark)

    Ramos, Tania; Veltzé, Sune; Reddy Sudireddy, Bhaskar;

    2014-01-01

    at 850°C, 50% H2O/H2 decreased in the order Ni/CGO≫Pd/CGO > Ru/CGO. After 200h of exposure Ru/CGO not only continued to exhibit low impedance, with final total Rp ≅ 0.02 Ωcm2, but also negligible degradation. For comparison, Ni/CGO degraded close to a factor of 3 to ca. 0.25 Ωcm2 in an equivalent period...

  9. Stoichiometric SrTiO3 Films via High Pressure Oxygen Sputter Deposition

    Science.gov (United States)

    Ambwani, Palak; Jalan, Bharat; Leighton, Chris

    2013-03-01

    Defect management in epilayers of semiconducting complex oxides such as SrTiO3 is a topic of considerable contemporary interest. Recent work has shown that sufficiently precise control over stoichiometry and defects in SrTiO3 enables facile n-type doping, record high mobilities, and even simultaneous observation of quantum oscillations and superconductivity. Such progress has typically been made using techniques such as oxygen/LASER MBE or high-temperature PLD. In this work we demonstrate, via homoepitaxy on SrTiO3(001), that RF high pressure oxygen sputtering from a ceramic target is similarly capable of growth of high-quality, stoichiometric SrTiO3 films. We show that optimization of the deposition temperature (above 750 °C) and oxygen pressure (above 2.5 mBar) leads to the deposition of films indistinguishable from the substrate via grazing incidence and wide-angle x-ray scattering. The importance of a pre-treatment of the substrates in oxygen above 900 °C is emphasized. The defect density/stoichiometry was further probed via the transport properties of vacuum annealed samples with controlled O vacancy density. Finally, we also demonstrate that the stoichiometry and defect density of films deposited under non-optimal conditions can be remarkably improved via post-deposition heat treatment. Work supported by NSF DMR and NSF MRSEC.

  10. Structure and properties of Li-rich Zn-doped LiNbO3 Crystal

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The Li-rich Zn-doped LiNbO3 (LN) crystals were grown by the Czochralski method. The structure of the crystals was measured by ultraviolet-visible absorption spectra. The results indicated that the Li-rich Zn-doped LN crystals had the same characteristics as the pure LN crystal. After Zn2+ entered into the lattice of Li-rich Zn-doped LN crystal, it replaced NbLi firstly. When there was no NbLi, Zn2+ replaced Li+ then. The second harmonic generation (SHG) property of Li-rich Zn-doped LiNbO3 crystal was measured. The results showed that the SHG conversation efficiency of Li-rich Zn-doped LiNbO3 crystals was higher than that of Zn-doped LiNbO3 crystals.

  11. Impact of biaxial compressive strain on the heterostructures of paraelectrics KTaO3 and SrTiO3

    Directory of Open Access Journals (Sweden)

    Yi Yang

    2015-05-01

    Full Text Available We have performed density functional theory calculations to explore the impact of biaxial compressive strain on the heterostructures of paraelectrics KTaO3 and SrTiO3. We find that the strain induces strong ferroelectric distortion in KTaO3/SrTiO3 heterostructures and it stabilizes the heterostructures in ferroelectric states.The strain influences the distribution of doped holes and leads to the localization of holes in TiO2 layer. It is very interesting that ferroelectricity and ferromagnetism simultaneously present in the strained heterostructures formed by the paraelectrics KTaO3 and SrTiO3. The reversal of ferroelectric polarization changes the interface magnetization and thus results in magnetoelectric coupling effect in the heterostructures.

  12. Upconversion Luminescence of SrTiO3:Er3+ Ultrafine Powders Produced by 785 nm Laser

    Institute of Scientific and Technical Information of China (English)

    Hai Guo; Yan-min Qiao; Ju-fang Zheng; Lei-hong Zhao

    2008-01-01

    Er3+ doped SrTiO3 ultrafine powders were prepared by solid state reaction in a molten NaCl flux. The structural properties were characterized by X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The Stokes emission spectra of Er3+ in SrTiO3:Er3+ ranging from green to near infrared region were investigated under 514.5 nm laser excitation. The green and red upconverted luminescence spectra of Er3+ were measured under excitation into the 4I9/2 level by 785 nm laser. The upconversion mechanisms were studied in detail through laser power dependence and Er3+ ion concentration dependence of upconverted emissions, and results show that excited state absorption and energy transfer process are the possible mechanisms for the upconversion. The upconversion properties indicate that SrTiO3:Er3+ may be used in upconversion phosphors.

  13. Quantization of Hall Resistance at the Metallic Interface between an Oxide Insulator and SrTiO3

    DEFF Research Database (Denmark)

    Trier, Felix; Prawiroatmodjo, Guenevere E. D. K.; Zhong, Zhicheng;

    2016-01-01

    The two-dimensional metal forming at the interface between an oxide insulatorand SrTiO3 provides new opportunities for oxide electronics. However, the quantum Hall effect, one of the most fascinating effects of electrons confined in two dimensions, remains underexplored at these complex oxide...... heterointerfaces. Here, we report the experimental observation of quantized Hall resistance in a SrTiO3 heterointerface based on the modulation-doped amorphous-LaAlO3/SrTiO3 heterostructure, which exhibits both highelectron mobility exceeding 10, 000 cm2/V s and low carrier density on the order of ~1012 cm-2....... Along with unambiguous Shubnikov-de Haasoscillations, the spacing of the quantized Hall resistance suggests that the interface is comprised of a single quantum well with ten parallel conducting two-dimensional subbands. This provides new insight into the electronic structure of conducting oxide...

  14. 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.

  15. Defects, stoichiometry, and electronic transport in SrTiO3-δ epilayers: A high pressure oxygen sputter deposition study

    Science.gov (United States)

    Ambwani, P.; Xu, P.; Haugstad, G.; Jeong, J. S.; Deng, R.; Mkhoyan, K. A.; Jalan, B.; Leighton, C.

    2016-08-01

    SrTiO3 is not only of enduring interest due to its unique dielectric, structural, and lattice dynamical properties, but is also the archetypal perovskite oxide semiconductor and a foundational material in oxide heterostructures and electronics. This has naturally focused attention on growth, stoichiometry, and defects in SrTiO3, one exciting recent development being such precisely stoichiometric defect-managed thin films that electron mobilities have finally exceeded bulk crystals. This has been achieved only by molecular beam epitaxy, however (and to a somewhat lesser extent pulsed laser deposition (PLD)), and numerous open questions remain. Here, we present a study of the stoichiometry, defects, and structure in SrTiO3 synthesized by a different method, high pressure oxygen sputtering, relating the results to electronic transport. We find that this form of sputter deposition is also capable of homoepitaxy of precisely stoichiometric SrTiO3, but only provided that substrate and target preparation, temperature, pressure, and deposition rate are carefully controlled. Even under these conditions, oxygen-vacancy-doped heteroepitaxial SrTiO3 films are found to have carrier density, mobility, and conductivity significantly lower than bulk. While surface depletion plays a role, it is argued from particle-induced X-ray emission (PIXE) measurements of trace impurities in commercial sputtering targets that this is also due to deep acceptors such as Fe at 100's of parts-per-million levels. Comparisons of PIXE from SrTiO3 crystals and polycrystalline targets are shown to be of general interest, with clear implications for sputter and PLD deposition of this important material.

  16. Effect of Lanthanum Doping on Ferroelectric and Strain Properties of 0.96Bi1/2(Na0.84K0.16)1/2TiO3-0.04SrTiO3 Lead-Free Ceramics

    Science.gov (United States)

    Tran, Vu Diem Ngoc; Ullah, Aman; Dinh, Thi Hinh; Lee, Jae-Shin

    2016-05-01

    Lead-free 0.96[Bi1/2(Na0.84K0.16)1/2](1- x)La x TiO3-0.04SrTiO3 (BNKTLa x-ST, with x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) ceramics have been synthesized using a conventional solid-state reaction method and their phase transition, dielectric, ferroelectric, and strain properties investigated. X-ray diffraction patterns revealed formation of pure perovskite phase. A phase transition from coexistence of rhombohedral and tetragonal to a pseudocubic phase was observed at x = 0.02. Polarization and bipolar strain hysteresis loops indicated that the ferroelectric order (FE) of BNKT-ST is significantly disrupted by lanthanum doping. The destabilization of the FE order results in degradation of the remanent polarization, coercive field, depolarization temperature ( T d), electromechanical coupling factor ( k p), and static d 33, accompanied by large electric-field-induced strain of 0.34% at 60 kV/cm with normalized strain of d 33 * = S max/ E max = 600 pm/V at a critical composition of around x = 0.02.

  17. 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.

  18. Electron gas induced in SrTiO3

    Science.gov (United States)

    Fu, Han; Reich, K. V.; Shklovskii, B. I.

    2016-03-01

    This mini-review is dedicated to the 85th birthday of Prof. L.V. Keldysh, from whom we have learned so much. In this paper, we study the potential and electron density depth profiles in surface accumulation layers in crystals with a large and nonlinear dielectric response such as SrTiO3 (STO) in the cases of planar, spherical, and cylindrical geometries. The electron gas can be created by applying an induction D 0 to the STO surface. We describe the lattice dielectric response of STO using the Landau-Ginzburg free energy expansion and employ the Thomas-Fermi (TF) approximation for the electron gas. For the planar geometry, we arrive at the electron density profile n( x) ∝ ( x + d)-12/7, where d ∝ D 0 -12/7 . We extend our results to overlapping electron gases in GTO/STO/GTO heterojunctions and electron gases created by spill-out from NSTO (heavily n-type doped STO) layers into STO. Generalization of our approach to a spherical donor cluster creating a big TF atom with electrons in STO brings us to the problem of supercharged nuclei. It is known that for an atom with a nuclear charge Ze where Z > 170, electrons collapse onto the nucleus, resulting in a net charge Zn physics, the collapse is caused by the nonlinear dielectric response. Electrons collapse into the charged spherical donor cluster with radius R when its total charge number Z exceeds the critical value Z c ≈ R/ a, where a is the lattice constant. The net charge e Z n grows with Z until Z exceeds Z* ≈ ( R/ a)9/7. After this point, the charge number of the compact core Z n remains ≈ Z*, with the rest Z* electrons forming a sparse TF atom with it. We extend our studies of collapse to the case of long cylindrical clusters as well.

  19. Enhanced self-repairing capability of sol-gel derived SrTiO3/nano Al2O3 composite films

    Science.gov (United States)

    Yao, Manwen; Peng, Yong; Xiao, Ruihua; Li, Qiuxia; Yao, Xi

    2016-08-01

    SrTiO3/nano Al2O3 inorganic nanocomposites were prepared by using a conventional sol-gel spin coating process. For comparison, SrTiO3 films doped by equivalent amount of sol-Al2O3 have also been investigated. Aluminum deposited by using vacuum evaporation was used as the top electrode. The nanocomposites exhibited a significantly enhanced dielectric strength of 506.9 MV/m, which was increased by 97.4% as compared with the SrTiO3 films doped with sol-Al2O3. The leakage current maintained of the same order of microampere until the ultimate breakdown of the nanocomposites. The excellent electrical performances are ascribed to the anodic oxidation reaction in origin, which can repair the internal and/or surface defects of the films.

  20. Effect of Nb Doping on High Temperature Oxidation Resistance of Ti-Al Alloyed Coatings

    Directory of Open Access Journals (Sweden)

    DAI Jing-jie

    2017-02-01

    Full Text Available Ti-Al alloyed coatings with different Nb doping contents were fabricated on TC4 titanium alloy by laser surface alloying to improve high temperature oxidation resistance of the alloy. Structures and high temperature oxidation behaviors of the alloyed coatings were analyzed and tested by X-ray diffraction (XRD, scanning electron microscope (SEM, energy dispersive spectrometer (EDS and box-type resistance furnace. The results show that the alloyed coatings consist of TiAl and Ti3Al, and no niobium compound are formed in Ti-Al-Nb alloyed coatings. The alloyed coatings are uniform and exhibit excellent metallurgical bonding with the substrates. A large amount of surface cracks and a few penetrating cracks are formed in Ti-Al alloyed coating without Nb doping, while no obvious cracks are formed in Ti-Al alloyed coating with Nb doping. The oxidation mass gains of all the alloyed coatings were significantly lower than those of the substrate. The alloyed coatings with Nb doping exhibit more excellent high temperature oxidation resistance due to the beneficial machanism of Nb doping. The mechanism of Nb doping on improving high temperature oxidation resistance of Ti-Al alloyed coatings includes reducing the defect concentration of TiO2, refining oxide grains and promoting the formation of Al2O3.

  1. 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

  2. Surface segregation in Nb-doped BaTiO{sub 3} films

    Energy Technology Data Exchange (ETDEWEB)

    Arveux, Emmanuel, E-mail: arveux@icmcb-bordeaux.cnrs.fr [ICMCB-CNRS, University of Bordeaux, 87 Avenue, Dr. A. Schweitzer, Pessac 33608 (France); Darmstadt University of Technology, Institute of Materials Science, Petersenstrasse 23, D-64287 Darmstadt (Germany); Payan, Sandrine; Maglione, Mario [ICMCB-CNRS, University of Bordeaux, 87 Avenue, Dr. A. Schweitzer, Pessac 33608 (France); Klein, Andreas [Darmstadt University of Technology, Institute of Materials Science, Petersenstrasse 23, D-64287 Darmstadt (Germany)

    2010-08-15

    We have used in situ photoemission spectroscopy to investigate Niobium doping in polycristalline BaTiO{sub 3}. The valence band maximum position progressively shifts from 2.5 eV for undoped to 2.84 eV for Nb-doped films. Ceramics and single crystal have been investigated for comparison with thin films. Nb-doped BaTiO{sub 3} ceramics and Nb-doped SrTiO{sub 3} single crystal show higher Fermi level position indicating that our doped films are less conducting regarding their bulk parents. This was confirmed by impedance spectroscopy under variable temperature. Large amount of niobium is clearly observable at surface but the amount of dopant is drastically reduced below the near-surface region, as evidenced by depth profile. Therefore, we provide evidence of surface segregation which would explain the contrasted resistivity values reported in literature for such donor-doped films.

  3. 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, Kangheon

    2017-01-04

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

  4. Defect Complex Effect in Nb Doped TiO2 Ceramics with Colossal Permittivity

    Science.gov (United States)

    Li, Fuchao; Shang, Baoqiang; Liang, Pengfei; Wei, Lingling; Yang, Zupei

    2016-10-01

    Donor-doped Nb x Ti1- x O2 ( x = 1%, 2%, 4%, 6%, and 8%) ceramics with giant permittivity (>104) and a very low dielectric loss (˜0.05) were sintered under flowing N2 at 1400°C for 10 h. By increasing Nb doping concentration, two different dielectric responses were evidenced in the frequency dependence of dielectric properties of Nb doped TiO2 ceramics, which corresponded to the space charge polarization and the electron-pinned defect-dipoles effect, respectively. Especially, combined with the x-ray photoelectron spectroscopy results, the electron-pinned defect-dipoles induced by the 2({Nb}^{5 + } )_{{Ti}}^{ bullet } to 4({Ti}^{3 + } )^'_{{Ti}} leftarrow {V}_{{o}}^{ bullet bullet } defect complex were further confirmed to give rise to both their high ɛr and low tan δ in the high frequency range for the Nb x Ti1- x O2 ceramics with x > 4%.

  5. Visible Light Photocatalytic Properties of Ta and N Codoped SrTiO3 Nanoparticles

    Directory of Open Access Journals (Sweden)

    Uyi Sulaeman

    2010-01-01

    Full Text Available Ta and N co-doped SrTiO3 was synthesized by microwave-assisted solvothermal reaction using SrCl2⋅6H2O, Ti(OC3H74, TaCl5, and HMT (hexamethylenetetramine in KOH and oleic acid mixed solutions. The products were characterized by XRD, TG-DTA, BET surface area measurement, TEM, EDX, DRS, PL-Spectra, and XPS. The nanoparticles of perovskite-type SrTi1-xTaxO3-yNy (x=0−0.1 were successfully synthesized. The photocatalytic activity of SrTiO3 for DeNOxability in the visible light region could be improved by the codoping of Ta5+ and N3-. The excellent visible light photocatalytic activity of this substance may be due to the generation of a new band gap by doping nitrogen that enables the absorption of visible light as well as a decrease in the incidence of the lattice defects, which acts as a recombination center of photo-induced electrons and holes by codoping with Ta5+.

  6. Electronic coupling between a FeSe monolayer film and SrTiO3 substrate

    Science.gov (United States)

    Huang, Y. N.; Pickett, W. E.

    2017-04-01

    Several experimental groups have reported superconductivity in single unit cell layers of FeSe on SrTiO3 and a few other substrates, with critical temperature Tc reports ranging up to 100 K, and a variety of theoretical work has been done. Here we examine more closely the interaction of a single FeSe layer with a TiO2 terminated SrTiO3(001) (STO) substrate. Several situations are analyzed: the underlying ideal interface, the effect of z -polarized longitudinal optic [LO ( z ̂ )] phonons in STO, electron doping of the STO substrate, substitution of Se by the bordering chalcogenides S and Te, and doping by adsorption of K on the FeSe surface. These results complement earlier studies of O and Se vacancies. The O py,py surface band of STO persists at the interface, and by sharing holes with the hole pocket of FeSe it plays a part in the behavior around the interface, initially by determining the Fe Fermi level lineup with the STO band gap. The LO (z ̂) mode causes strong band shifts around the interface but the strength of coupling to the Fe bands cannot be obtained with our methods. Adsorption of 25% K (one K per four Fe) fills the small O interface hole pocket and donates the rest of the electrons to the Fe hole pockets, filling them.

  7. Thin-film dye sensitization and impurity effects on TiO2 and SrTiO3 electrodes for the photoelectrolysis of water

    NARCIS (Netherlands)

    Mackor, A.; Schoonman, J.

    1980-01-01

    Single crystals of TiO2 and SrTiO3 are sensitized by thin films of a ruthenium surfactant dye, which is able to sustain catalytic oxidation of water upon irradiation with visible light. Calculated turnover numbers exceed 2000. Doping of the crystals with niobium does not improve the suitability of t

  8. Thin-film dye sensitization and impurity effects on TiO2 and SrTiO3 electrodes for the photoelectrolysis of water

    NARCIS (Netherlands)

    Mackor, A.; Schoonman, J.

    1980-01-01

    Single crystals of TiO2 and SrTiO3 are sensitized by thin films of a ruthenium surfactant dye, which is able to sustain catalytic oxidation of water upon irradiation with visible light. Calculated turnover numbers exceed 2000. Doping of the crystals with niobium does not improve the suitability of

  9. High-T(c) Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides.

    Science.gov (United States)

    Di Castro, D; Cantoni, C; Ridolfi, F; Aruta, C; Tebano, A; Yang, N; Balestrino, G

    2015-10-02

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low T(c). We report the occurrence of high T(c) superconductivity in the bilayer CaCuO(2)/SrTiO(3), where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO(2)/SrTiO(3) interface must be realized between the Ca plane of CaCuO(2) and the TiO(2) plane of SrTiO(3). Only in this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO(2) planes. A detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO(2) unit cells close to the interface with SrTiO(3). The results obtained for the CaCuO(2)/SrTiO(3) interface can be extended to multilayered high T(c) cuprates, contributing to explaining the dependence of T(c) on the number of CuO(2) planes in these systems.

  10. Electrical Conductivity, Thermoelectric Power, and Equilibration Kinetics of Nb-Doped TiO2.

    Science.gov (United States)

    Nowotny, Janusz; Bak, Tadeusz; Dickey, Elisabeth C; Sigmund, Wolfgang; Alim, Mohammad A

    2016-09-01

    This work considers the equilibration kinetics of Nb-doped TiO2 single crystal (0.066 atom % Nb) during oxidation and reduction within a wide range of temperature (1073-1298 K) and oxygen activity (10(-14)-10(5) Pa). The associated semiconducting properties were determined using simultaneous measurements of both electrical conductivity and thermoelectric power. It is shown that the chemical diffusion coefficient in the strongly reducing regime, p(O2) Nb-doped TiO2 single crystal (this work) and polycrystalline Nb-doped TiO2 (reported before) indicates that the gas/solid kinetics for the polycrystalline specimen at higher oxygen activities is rate controlled by the transport of oxygen within individual grains.

  11. Growth and optical properties of Nb-doped WS2 monolayers

    Science.gov (United States)

    Sasaki, Shogo; Kobayashi, Yu; Liu, Zheng; Suenaga, Kazutomo; Maniwa, Yutaka; Miyauchi, Yuhei; Miyata, Yasumitsu

    2016-07-01

    We report the chemical vapor deposition growth of Nb-doped WS2 monolayers and their characterization. Electron microscopy observations reveal that the Nb atom was substituted at the W site at a rate of approximately 0.5%. Unlike Mo doping, Nb-doped samples have photoluminescence (PL) peaks at 1.4-1.6 eV at room temperature. The peak energies are lower than the optical bandgap of 1.8 eV, and a saturation behavior of PL intensity is observed with the increase in excitation power. These results indicate that the observed PL peaks are assignable to the emission from impurity states generated by the substitution of Nb.

  12. NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

    Directory of Open Access Journals (Sweden)

    Tae Ho Yeom

    2016-04-01

    Full Text Available In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  13. Tuning of near-infrared luminescence of SrTiO3:Ni2+ thin films grown on piezoelectric PMN-PT via strain engineering.

    Science.gov (United States)

    Bai, Gongxun; Zhang, Yang; Hao, Jianhua

    2014-07-17

    We report the tunable near-infrared luminescence of Ni(2+) doped SrTiO3 (STO:Ni) thin film grown on piezoelectric Pb(Mg(1/3)Nb(2/3))(0.7)Ti(0.3)O3 (PMN-PT) substrate via strain engineering differing from conventional chemical approach. Through controlling the thickness of STO:Ni film, the luminescent properties of the films including emission wavelength and bandwidth, as well as lifetime can be effectively tuned. The observed phenomena can be explained by the variation in the crystal field around Ni(2+) ions caused by strain due to the lattice mismatch. Moreover, the modulation of strain can be controlled under an external electric field via converse piezoelectric effect of PMN-PT used in this work. Consequently, controllable emission of the STO:Ni thin film is demonstrated in a reversible and real-time way, arising from the biaxial strain produced by piezoelectric PMN-PT. Physical mechanism behind the observation is discussed. This work will open a door for not only investigating the luminescent properties of the phosphors via piezoelectric platform, but also potentially developing novel planar light sources.

  14. Structural and vibrational investigations of Nb-doped TiO{sub 2} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Uyanga, E., E-mail: uyanga.enkhnaran@gmail.com [Institute of Physics and Technology, Mongolian Academy of Sciences, Enkhtaivan Avenue 54B, Ulaanbaatar 13330 (Mongolia); Frank Laboratory of Neutron Physics, JINR, Dubna 141980 (Russian Federation); Gibaud, A.; Daniel, P. [LUNAM Université, Université du Maine, CNRS UMR 6283, Institut des molécules et matériaux et du Mans–IMMM, Avenue Olivier Messiaen, Le Mans 72085 Cedex 9 (France); Sangaa, D.; Sevjidsuren, G.; Altantsog, P. [Institute of Physics and Technology, Mongolian Academy of Sciences, Enkhtaivan Avenue 54B, Ulaanbaatar 13330 (Mongolia); Beuvier, T. [LUNAM Université, Université du Maine, CNRS UMR 6283, Institut des molécules et matériaux et du Mans–IMMM, Avenue Olivier Messiaen, Le Mans 72085 Cedex 9 (France); Lee, Chih Hao [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Balagurov, A.M. [Frank Laboratory of Neutron Physics, JINR, Dubna 141980 (Russian Federation)

    2014-12-15

    Highlights: • We studied the evolutions of structure for TiO{sub 2} thin film as changes with Nb doping and temperatures. • Up to 800 °C, the grain size of Nb{sub 0.1}Ti{sub 0.9}O{sub 2} is smaller than for pure TiO{sub 2} because doped Nb hinders the growth of the TiO{sub 2} grains. • There was no formation of the rutile phase at high temperature. • Nb doped TiO{sub 2} films have high electron densities at 400–700 °C. • Nb dope extends the absorbance spectra of TiO{sub 2} which leads to the band gap reduce. - Abstract: Acid-catalyzed sol–gel and spin-coating methods were used to prepare Nb-doped TiO{sub 2} thin film. In this work, we studied the effect of niobium doping on the structure, surface, and absorption properties of TiO{sub 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{sup 5+} ions into the lattice. The band gap energy of indirect transition of the TiO{sub 2} thin films was calculated to be about 3.03 eV. After niobium doping, it decreased to 2

  15. 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

  16. Hazardous Doping for Photo-Electrochemical Conversion: The Case of Nb-Doped Fe2O3 from First Principles

    Directory of Open Access Journals (Sweden)

    Natav Yatom

    2015-11-01

    Full Text Available The challenge of improving the efficiency of photo-electrochemical devices is often addressed through doping. However, this strategy could harm performance. Specifically, as demonstrated in a recent experiment, doping one of the most widely used materials for water splitting, iron (III oxide (Fe2O3, with niobium (Nb can still result in limited efficiency. In order to better understand the hazardous effect of doping, we use Density Functional Theory (DFT+U for the case of Nb-doped Fe2O3. We find a direct correlation between the charge of the dopant, the charge on surface of the Fe2O3 material, and the overpotential required for water oxidation reaction. We believe that this work contributes to advancing our understanding of how to select effective dopants for materials.

  17. Quadratic nonlinear optical parameters of 7% MgO-doped LiNbO3 crystal

    Science.gov (United States)

    Kulyk, B.; Kapustianyk, V.; Figà, V.; Sahraoui, B.

    2016-06-01

    Pure and 7% MgO-doped lithium niobate (LiNbO3) single crystals were grown by the Czochralski technique. The shift of optical absorption edge in 7% MgO-doped crystal in direction of shorter wavelength compared to undoped crystal was observed. The second harmonic generation measurements of 7% MgO-doped LiNbO3 crystal were performed at room temperature by means of the rotational Maker fringe technique using Nd:YAG laser generating at 1064 nm in picoseconds regime. Experimentally obtained value of nonlinear optical coefficient d33 for 7% MgO-doped LiNbO3 was found to be less than for undoped crystal but higher than for 5% MgO-doped. I-type phase-matched second harmonic generation was achieved and the value of phase-matched angle was calculated. High quadratic nonlinearity together with tolerance to intensive laser irradiation makes 7% MgO-doped LiNbO3 crystal interesting for application in optoelectronics.

  18. Hydrogenation and Ammoniation of SrTiO3 for an Enhanced Visible-light Photocatalysis

    Institute of Scientific and Technical Information of China (English)

    Tao Sun; You-yuan Zhao; Ming Lu

    2012-01-01

    Hydrogenation and ammoniation of SrTiO3 (STO),a normal ultraviolet photocatalyst,were performed by annealing STO〈100〉 in H2:N2=5%:95% and NH3,respectively,at various temperatures T.It was found that hydrogenation at T≥900 ℃ remarkably enhanced the UV photocatalytic ability of STO,but the visible-light photocatalysis was still unavailable,while ammoniation at T≥800 ℃ introduced the N doping,resulting in visible-light photocatalytic activity.Furthermore,when a hydrogenated STO was subjected to ammoniation,the visible-light photocatalytic ability was nearly the same as that of the ammoniated one; but the hydrogenation of an ammoniated one significantly enhanced visible-light photocatalysis,indicating a synergetic effect of hydrogenation and ammoniation.Discussions and identifications have been made to analyze these results.

  19. Oxygen vacancies in strained SrTiO3 thin films: Formation enthalpy and manipulation

    Science.gov (United States)

    Iglesias, L.; Sarantopoulos, Alexandros; Magén, C.; Rivadulla, F.

    2017-04-01

    We report the enthalpy of oxygen vacancy formation in thin films of electron-doped SrTiO3, under different degrees of epitaxial stress. We demonstrate that both compressive and tensile strain decrease this energy at a very similar rate and promote the formation of stable doubly ionized oxygen vacancies. Moreover, we also show that unintentional cationic vacancies introduced under typical growth conditions, produce a characteristic rotation pattern of TiO6 octahedra. The local concentration of oxygen vacancies can be modulated by an electric field with an AFM tip, changing not only the local electrical potential but also producing a nonvolatile mechanical response whose sign (up/down) can be reversed by the electric field.

  20. 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.

  1. 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}.

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

    Science.gov (United States)

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

    2016-10-01

    In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO2 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 TiO2 surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase JSC of the surface while slightly decreasing VOC compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

  3. 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....

  4. Atomic layer deposition of Nb-doped ZnO for thin film transistors

    Science.gov (United States)

    Shaw, A.; Wrench, J. S.; Jin, J. D.; Whittles, T. J.; Mitrovic, I. Z.; Raja, M.; Dhanak, V. R.; Chalker, P. R.; Hall, S.

    2016-11-01

    We present physical and electrical characterization of niobium-doped zinc oxide (NbZnO) for thin film transistor (TFT) applications. The NbZnO films were deposited using atomic layer deposition. X-ray diffraction measurements indicate that the crystallinity of the NbZnO films reduces with an increase in the Nb content and lower deposition temperature. It was confirmed using X-ray photoelectron spectroscopy that Nb5+ is present within the NbZnO matrix. Furthermore, photoluminescence indicates that the band gap of the ZnO increases with a higher Nb content, which is explained by the Burstein-Moss effect. For TFT applications, a growth temperature of 175 °C for 3.8% NbZnO provided the best TFT characteristics with a saturation mobility of 7.9 cm2/Vs, the current On/Off ratio of 1 × 108, and the subthreshold swing of 0.34 V/decade. The transport is seen to follow a multiple-trap and release mechanism at lower gate voltages and percolation thereafter.

  5. Atomic Defects and Doping of Monolayer NbSe2.

    Science.gov (United States)

    Nguyen, Lan; Komsa, Hannu-Pekka; Khestanova, Ekaterina; Kashtiban, Reza J; Peters, Jonathan J P; Lawlor, Sean; Sanchez, Ana M; Sloan, Jeremy; Gorbachev, Roman V; Grigorieva, Irina V; Krasheninnikov, Arkady V; Haigh, Sarah J

    2017-02-24

    We have investigated the structure of atomic defects within monolayer NbSe2 encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reveal that adventitious impurities of C, N, and O can substitute into the NbSe2 lattice stabilizing Se divacancies. We further observe evidence of Pt substitution into both Se and Nb vacancy sites. This knowledge of the character and relative frequency of different atomic defects provides the potential to better understand and control the unusual electronic and magnetic properties of this exciting two-dimensional material.

  6. Effects of Rare-Earth La2O3 Addition on Microstructures and Electrical Properties of SrTiO3 Varistor-Capacitor Dual Functional Ceramics

    Institute of Scientific and Technical Information of China (English)

    Ji Huiming; Li Cuixia; Meng Hui; Gan Guoyou; Yan Jikang

    2005-01-01

    The effects of rare-earth La2O3 addition on microstructures and electrical properties of SrTiO3 ceramics were investigated. Semiconductor SrTiO3-based voltage-sensing and dielectric dual functional ceramics was prepared by a single step sintering technology in this study, and the effects of the content of La2O3 on characteristics of the product were discussed in terms of microstructures and electrical properties of materials. The results show that SrTiO3-based ceramics doped with La2O3 exhibits more homogeneous grain distribution, greater grain size, and excellent voltage sensing and dielectric characteristics than those without La2O3 doping. The samples doped with 1.1% La2O3 were sintered at 1420 ℃ in N2+C weak reducing atmosphere. The average grain size of the samples doped with La2O3 is 40 μm, the breakdown voltage of 19.7 V*mm-1, the nonlinear exponent of 7.2, and dielectric constant of 22500. The results reveal that final products are suitable to use in low operating voltage.

  7. Verification of redox-processes as switching and retention failure mechanisms in Nb:SrTiO3/metal devices

    Science.gov (United States)

    Baeumer, C.; Raab, N.; Menke, T.; Schmitz, C.; Rosezin, R.; Müller, P.; Andrä, M.; Feyer, V.; Bruchhaus, R.; Gunkel, F.; Schneider, C. M.; Waser, R.; Dittmann, R.

    2016-07-01

    Nanoscale redox reactions in transition metal oxides are believed to be the physical foundation of memristive devices, which present a highly scalable, low-power alternative for future non-volatile memory devices. The interface between noble metal top electrodes and Nb-doped SrTiO3 single crystals may serve as a prominent but not yet well-understood example of such memristive devices. In this report, we will present experimental evidence that nanoscale redox reactions and the associated valence change mechanism are indeed responsible for the resistance change in noble metal/Nb-doped SrTiO3 junctions with dimensions ranging from the micrometer scale down to the nanometer regime. Direct verification of the valence change mechanism is given by spectromicroscopic characterization of switching filaments. Furthermore, it is found that the resistance change over time is driven by the reoxidation of a previously oxygen-deficient region. The retention times of the low resistance states, accordingly, can be dramatically improved under vacuum conditions as well as through the insertion of a thin Al2O3 layer which prevents this reoxidation. These insights finally confirm the resistive switching mechanism at these interfaces and are therefore of significant importance for the study and application of memristive devices based on Nb-doped SrTiO3 as well as systems with similar switching mechanisms.Nanoscale redox reactions in transition metal oxides are believed to be the physical foundation of memristive devices, which present a highly scalable, low-power alternative for future non-volatile memory devices. The interface between noble metal top electrodes and Nb-doped SrTiO3 single crystals may serve as a prominent but not yet well-understood example of such memristive devices. In this report, we will present experimental evidence that nanoscale redox reactions and the associated valence change mechanism are indeed responsible for the resistance change in noble metal/Nb-doped Sr

  8. Effect of Nb-doped TiO2 on nanocomposited aligned ZnO nanorod/TiO2:Nb for dye-sensitized solar cells

    Science.gov (United States)

    Saurdi, I.; Shafura, A. K.; Azhar, N. E. A.; Ishak, A.; Malek, M. F.; Alrokayan, A. H. Salman; Khan, Haseeb A.; Mamat, M. H.; Rusop, M.

    2016-07-01

    The Nb-doped TiO2 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 TiO2 films were deposited on top of aligned ZnO Nanorod on ITO glass substrates using spin coating technique. The nanocomposited aligned ZnO nanorod/Nb-doped TiO2 (TiO2: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/TiO2: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/TiO2:Nb-5at.%.

  9. 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.

  10. Influence of Mg doping on refractive index of LiNbO{sub 3} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sisodia, N. [Holkar Science College, Department of Physics, Indore (India); Trivedi, R.; Choubey, R.K.; Sen, P.; Sen, P.K. [Shri G.S. Institute of Technology and Science, Department of Applied Physics, Indore (India); Kar, S.; Bartwal, K.S. [Raja Ramanna Centre for Advanced Technology, Laser Materials Development and Devices Division, Indore (India)

    2006-08-15

    Congruent, 3, 5 and 7 mol % Mg doped LiNbO{sub 3} single crystals have been grown by Czochralski technique. The transmittance and refractive indices are measured experimentally. The experimental results are supported with a theoretical analysis based upon density matrix approach where we have included the dipolar contribution. (orig.)

  11. Effects of nonmetal doping on electronic structures of NaNbO3 based on hybrid density functional calculation

    Science.gov (United States)

    Shi, Haifeng; Lan, Benyue; Zhang, Chengliang; Ye, Enjia; Nie, Yanguang; Bian, Baoan

    2016-10-01

    The influences of a series of anion doping on the electronic structures of sodium niobate (NaNbO3) have been systematically investigated by density functional theory (DFT) calculations with the hybrid B3LYP functional. As for B(C,P)-doped NaNbO3, the isolated B 2p (C 2p, P 3p) states were formed above the valence band maximum (VBM) of NaNbO3, which were too weak to mix with O 2p states and thus produced band gap narrowing. While the band gap of NaNbO3 was slightly narrowed after F doping. As for S-doped NaNbO3, the S 3p states mixed with O 2p states well and thus reduced the band gap energy. According to the calculation results, we tentatively put forward that S doping would be appropriate for single anion doping NaNbO3, while the B(C,P) elements would be suitable candidates for co-doping NaNbO3.

  12. Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures.

    Science.gov (United States)

    Salluzzo, M; Gariglio, S; Stornaiuolo, D; Sessi, V; Rusponi, S; Piamonteze, C; De Luca, G M; Minola, M; Marré, D; Gadaleta, A; Brune, H; Nolting, F; Brookes, N B; Ghiringhelli, G

    2013-08-23

    Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.

  13. Electrospun Nb-doped TiO2 nanofiber support for Pt nanoparticles with high electrocatalytic activity and durability.

    Science.gov (United States)

    Kim, MinJoong; Kwon, ChoRong; Eom, KwangSup; Kim, JiHyun; Cho, EunAe

    2017-03-14

    This study explores a facile method to prepare an efficient and durable support for Pt catalyst of polymer electrolyte membrane fuel cell (PEMFC). As a candidate, Nb-doped TiO2 (Nb-TiO2) nanofibers are simply fabricated using an electrospinning technique, followed by a heat treatment. Doping Nb into the TiO2 nanofibers leads to a drastic increase in electrical conductivity with doping level of up to 25 at. % (Nb0.25Ti0.75O2). Pt nanoparticles are synthesized on the prepared 25 at. % Nb-doped TiO2-nanofibers (Pt/Nb-TiO2) as well as on a commercial powdered carbon black (Pt/C). The Pt/Nb-TiO2 nanofiber catalyst exhibits similar oxygen reaction reduction (ORR) activity to that of the Pt/C catalyst. However, during an accelerated stress test (AST), the Pt/Nb-TiO2 nanofiber catalyst retained more than 60% of the initial ORR activity while the Pt/C catalyst lost 65% of the initial activity. The excellent durability of the Pt/Nb-TiO2 nanofiber catalyst can be attributed to high corrosion resistance of TiO2 and strong interaction between Pt and TiO2.

  14. Electrospun Nb-doped TiO2 nanofiber support for Pt nanoparticles with high electrocatalytic activity and durability

    Science.gov (United States)

    Kim, Minjoong; Kwon, Chorong; Eom, Kwangsup; Kim, Jihyun; Cho, Eunae

    2017-03-01

    This study explores a facile method to prepare an efficient and durable support for Pt catalyst of polymer electrolyte membrane fuel cell (PEMFC). As a candidate, Nb-doped TiO2 (Nb-TiO2) nanofibers are simply fabricated using an electrospinning technique, followed by a heat treatment. Doping Nb into the TiO2 nanofibers leads to a drastic increase in electrical conductivity with doping level of up to 25 at. % (Nb0.25Ti0.75O2). Pt nanoparticles are synthesized on the prepared 25 at. % Nb-doped TiO2-nanofibers (Pt/Nb-TiO2) as well as on a commercial powdered carbon black (Pt/C). The Pt/Nb-TiO2 nanofiber catalyst exhibits similar oxygen reaction reduction (ORR) activity to that of the Pt/C catalyst. However, during an accelerated stress test (AST), the Pt/Nb-TiO2 nanofiber catalyst retained more than 60% of the initial ORR activity while the Pt/C catalyst lost 65% of the initial activity. The excellent durability of the Pt/Nb-TiO2 nanofiber catalyst can be attributed to high corrosion resistance of TiO2 and strong interaction between Pt and TiO2.

  15. Electrospun Nb-doped TiO2 nanofiber support for Pt nanoparticles with high electrocatalytic activity and durability

    Science.gov (United States)

    Kim, MinJoong; Kwon, ChoRong; Eom, KwangSup; Kim, JiHyun; Cho, EunAe

    2017-01-01

    This study explores a facile method to prepare an efficient and durable support for Pt catalyst of polymer electrolyte membrane fuel cell (PEMFC). As a candidate, Nb-doped TiO2 (Nb-TiO2) nanofibers are simply fabricated using an electrospinning technique, followed by a heat treatment. Doping Nb into the TiO2 nanofibers leads to a drastic increase in electrical conductivity with doping level of up to 25 at. % (Nb0.25Ti0.75O2). Pt nanoparticles are synthesized on the prepared 25 at. % Nb-doped TiO2-nanofibers (Pt/Nb-TiO2) as well as on a commercial powdered carbon black (Pt/C). The Pt/Nb-TiO2 nanofiber catalyst exhibits similar oxygen reaction reduction (ORR) activity to that of the Pt/C catalyst. However, during an accelerated stress test (AST), the Pt/Nb-TiO2 nanofiber catalyst retained more than 60% of the initial ORR activity while the Pt/C catalyst lost 65% of the initial activity. The excellent durability of the Pt/Nb-TiO2 nanofiber catalyst can be attributed to high corrosion resistance of TiO2 and strong interaction between Pt and TiO2. PMID:28290503

  16. 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.

  17. EXAFS simulations in Zn-doped LiNbO3 based on defect calculations

    Science.gov (United States)

    Valerio, Mário E. G.; Jackson, Robert A.; Bridges, Frank G.

    2017-02-01

    Lithium niobate, LiNbO3, is an important technological material with good electro-optic, acousto-optic, elasto-optic, piezoelectric and nonlinear properties. EXAFS on Zn-doped LiNbO3 found strong evidences that Zn substitutes primarily at the Li site on highly doped samples. In this work the EXAFS results were revisited using a different approach where the models for simulating the EXAFS results were obtained from the output of defect calculations. The strategy uses the relaxed positions of the ions surrounding the dopants to generate a cluster from where the EXAFS oscillations can be calculated. The defect involves not only the Zn possible substitution at either Li or Nb sites but also the charge compensating defects, when needed. From previous defect modelling, a subset of defects was selected based on the energetics of the defect production in the LiNbO3 lattice. From them, all possible clusters were generated and the simulated EXAFS were computed. The simulated EXAFS were them compared to available EXAFS results in the literature. Based on this comparison different models could be proposed to explain the behaviour of Zn in the LiNbO3 matrix.

  18. Highly transparent Nb-doped indium oxide electrodes for organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jun Ho; Seong, Tae-Yeon [Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of); Na, Seok-In [Professional Graduate School of Flexible and Printable Electronics, Chonbuk National University, 664-14, Deokjin-dong, Jeongju-si, Jellabuk-do 561-756 (Korea, Republic of); Chung, Kwun-Bum [Department of Physics, Dankook University, Mt. 29, Anseo-Dong, Chenan 330-714 (Korea, Republic of); Lee, Hye-Min; Kim, Han-Ki, E-mail: imdlhkkim@khu.ac.kr [Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, 1 Seocheon-dong, Yongin, Gyeonggi-do 446-701 (Korea, Republic of)

    2014-03-15

    The authors investigated the characteristics of Nb-doped In{sub 2}O{sub 3} (INbO) films prepared by co-sputtering of Nb{sub 2}O{sub 5} and In{sub 2}O{sub 3} for use in transparent anodes for organic solar cells (OSCs). To optimize the Nb dopant composition in the In{sub 2}O{sub 3} matrix, the effect of the Nb doping power on the resistivity and transparency of the INbO films were examined. The electronic structure and microstructure of the INbO films were also investigated using synchrotron x-ray absorption spectroscopy and x-ray diffraction examinations in detail. At the optimized Nb co-sputtering power of 30 W, the INbO film exhibited a sheet resistance of 15 Ω/sq, and an optical transmittance of 86.04% at 550 nm, which are highly acceptable for the use as transparent electrodes in the fabrication of OSCs. More importantly, the comparable power conversion efficiency (3.34%) of the OSC with an INbO anode with that (3.31%) of an OSC with a commercial ITO anode indicates that INbO films are promising as a transparent electrode for high performance OSCs.

  19. Theoretical study of hydrogen dissociation and diffusion on Nb and Ni co-doped Mg(0001): A synergistic effect

    Science.gov (United States)

    Chen, Ming; Cai, Zhen-Zhun; Yang, Xiao-Bao; Zhu, Min; Zhao, Yu-Jun

    2012-07-01

    The interaction of H2 with clean, Ni and Nb doped Mg(0001) surface are investigated by first-principles calculations. Individual Ni and Nb atoms within the outermost surface can reduce the dissociation barrier of the hydrogen molecule. They, however, prefers to substitute for the Mg atoms within the second layer, leading to a weaker catalytic effect for the dissociation of H2, a bottleneck for the hydriding of MgH2. Interestingly, co-doping of Ni and Nb stabilizes Ni at the first layer, and results in a significant reduction of the dissociation barrier of H2 on the Mg surface, coupled with an increase of the diffusion barrier of H. Although codoped Ni and Nb shows no remarkable advantage over single Nb here, it implies that the catalytic effect could be optimized by co-doping of "modest" transition metals with balanced barriers for dissociation of H2 and diffusion of H on Mg surfaces.

  20. SrTiO3 on piezoelectric PMN-PT(001) for application of variable strain

    Energy Technology Data Exchange (ETDEWEB)

    Bilani-Zeneli, Orkidia [IFW Dresden; Rata, D [IFW Dresden; Herklotz, A [IFW Dresden; Mieth, O [Technische Universitat Dresden; Eng, L. M. [TU Dresden; Schultz, Ludwig [Institut fur Metallische Werkstoffe, Dresden, Germany; Biegalski, Michael D [ORNL; Christen, Hans M [ORNL; Dorr, Kathrin [IFW Dresden

    2008-01-01

    SrTiO3 (STO) is the most frequently used substrate material for complex oxide films. In this work, STO is explored as a buffer layer on piezoelectric pseudocubic Pb(Mg1/3Nb2/3)0.72Ti0.28O3(001) (PMN-PT) substrates which serve to reversibly strain thin films. The STO buffer layer reduces the in-plane lattice parameter and allows for better lattice matching to broader range of thin film materials. STO films (30 nm) have been grown with epitaxial orientation on PMN-PT with an in-plane lattice parameter close to that of bulk STO. The substrate`s rhombohedral domain structure has been imaged by Atomic Force Microscopy (AFM). The related ferroelectric domain structure has been investigated by Piezoresponse Force Microscopy (PFM). Within a domain, STO grows with rather low roughness (rms < 0.2 nm). The transfer of the piezoelectric substrate strain to the STO film and its variation with an applied electric field is studied by x-ray diffraction. The strain dependence of the electrical resistance is measured for a ferromagnetic manganite film grown on top of the STO. Both experiments confirm qualitatively that the STO buffer transfers the substrate strain into a functional film deposited on top.

  1. Investigation of Boron-doping Effect on Photoluminescence Properties of CdNb2O6: Eu(3+) Phosphors.

    Science.gov (United States)

    Başak, Ali Sadi; Ekmekçi, Mete Kaan; Erdem, Murat; Ilhan, Mustafa; Mergen, Ayhan

    2016-03-01

    Pure, Eu(3+) - doped and Eu(3+),B(3+) co-doped CdNb2O6 powders have been prepared by a molten salt synthesis method using Li2SO4/Na2SO4 salt mixture as a flux at a relatively low temperatures as compared to solid state reaction. X-ray diffraction patterns of pure CdNb2O6 samples indicated orthorhombic single phase. Photoluminescence investigations of CdNb2O6 samples showed a strong blue emission band centered at 460 nm. For Eu-doped CdNb2O6 samples, the luminescence of Eu(3+) was observed with the host red emission varying with the Eu-doping concentrations. This PL characteristic of the doped samples may be attributed to the energy transfer between Eu(3+) and niobate groups (NbO6). Boron incorporation has remarkably increased the luminescence of Eu(3+)-doped CdNb2O6.

  2. 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.

  3. Optimization of atomically smooth and metallic surface of SrTiO3

    Science.gov (United States)

    Kwak, In Hae; Varnoosfaderani, Sima saeidi; Barquist, Colin S.; Paykar, Ashkan; Shakya, Ambika; Lee, Yoonseok; Hebard, Arthur F.; Biswas, Amlan

    2017-04-01

    We obtained metallic SrTiO3 with an atomically smooth surface, where the step height is close to the unit cell height of the crystal. After the surface treatments for generating the TiO2 terminated layer, the optimal conditions for vacuum annealing were found. The atomically smooth surface was verified by atomic force microscopy and lateral force microscopy. The temperature dependent resistance R(T) measured down to 52 mK indicates the metallic behavior, and its physical origin of the conduction was analyzed by fitting an equation involving electron-phonon and electron-electron scattering mechanisms. Our results are similar to R(T) reported for LaAlO3/SrTiO3 interfaces. In addition, the Hall effect measurement shows a clear resemblance between our reduced SrTiO3 and LaAlO3/SrTiO3 interfaces with sheet carrier density and Hall mobility. We expect that our treatments not only promote the usage of conducting SrTiO3 substrates for subsequent thin film growth but also contribute to the current research interest in two dimensional electron gas (2DEG) SrTiO3 and the interfaces between insulating oxides of LaAlO3/SrTiO3.

  4. Electrical and Seebeck effect measurements in Nb doped VO/sub 2/

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, B. (Technion-Israel Inst. of Tech., Haifa)

    1982-01-01

    The resistance of pure and Nb doped VO/sub 2/ and the Seebeck coefficient of Nb doped VO/sub 2/ have been measured in the temperature range of 78 to 360 K. A simple analysis of the results shows that above 140 K and below the transition temperature the effective density of states in the conduction band of VO/sub 2/ is of the order of (but larger than) one state per vanadium atom. This high effective density of states is consistent with the large effective mass (and low mobility) of electrons in this material. It is shown also that in this range, the temperature dependence of the electronic mobility in VO/sub 2/ is Tsup(-..gamma..) where ..gamma.. > approximately 2. Additional results are discussed in the text.

  5. 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......, and the uniformity of heating during the thermal dehydration step were found to have significant influence on the final phase purity of the material. Calcination at 1100 degrees C in 7% H-2 in N-2 produced single phase Nb-doped strontium titanate with grain sizes of about 100 nm in diameter on average. (c) 2007...

  6. Resistance switching of the interfacial conductance in amorphous SrTiO3 heterostructures

    DEFF Research Database (Denmark)

    Christensen, Dennis; Trier, Felix; Chen, Yunzhong

    Complex oxides have attracted a lot of interest recently as this class of material exhibits a plethora of remarkable properties. In particular, a great variety of properties is observed in the heterostructure composed of lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3). For instance...... by an electric field. It has previously been demonstrated that SrTiO3 heterostructures with amorphous LaAlO3 top layers can display interfacial conductivity with similar critical thickness dependence. Here, we report resistance switching of the interfacial conductance for SrTiO3 heterostructures with amorphous...

  7. Anomalous high mobility in LaAlO3/SrTiO3 nanowires.

    Science.gov (United States)

    Irvin, Patrick; Veazey, Joshua P; Cheng, Guanglei; Lu, Shicheng; Bark, Chung-Wung; Ryu, Sangwoo; Eom, Chang-Beom; Levy, Jeremy

    2013-02-13

    Nanoscale control of the metal-insulator transition at the interface between LaAlO(3) and SrTiO(3) provides a pathway for reconfigurable, oxide-based nanoelectronics. Four-terminal transport measurements of LaAlO(3)/SrTiO(3) nanowires at room temperature (T = 300 K) reveal an equivalent 2D Hall mobility greatly surpassing that of bulk SrTiO(3) and approaching that of n-type Si nanowires of comparable dimensions. This large enhancement of mobility is relevant for room-temperature device applications.

  8. Photoluminescence of monolayer MoS2 on LaAlO3 and SrTiO3 substrates.

    Science.gov (United States)

    Li, Yuanyuan; Qi, Zeming; Liu, Miao; Wang, Yuyin; Cheng, Xuerui; Zhang, Guobin; Sheng, Liusi

    2014-12-21

    In an atomically thin-film/dielectric-substrate heterostructure, the elemental physical properties of the atomically thin-film are influenced by the interaction between the thin-film and the substrate. In this article, utilizing monolayer MoS(2) on LaAlO(3) and SrTiO(3) substrates, as well as SiO2 and Gel-film as reference substrates similar to previously reported work [Nano Res, 2014, 7, 561], we systematically investigate the substrate effect on the photoluminescence of monolayer MoS(2). We observed significantly substrate-dependant photoluminescence of monolayer MoS(2), originating from substrate-to-film charge transfer. We found that SiO2 substrate introduces the most charge doping while SrTiO(3) introduces less charge transfer. Through the selection of desired substrate, we are able to induce different amounts of charge into the monolayer MoS(2), which consequently modifies the neutral exciton and charged exciton (trion) emissions. Finally, we proposed a band-diagram model to elucidate the relation between charge transfer and the substrate Fermi level and work function. Our work demonstrates that the substrate charge transfer exerts a strong influence on the monolayer MoS(2) photoluminescence property, which should be considered during device design and application. The work also provides a possible route to modify the thin-film photoluminescence property via substrate engineering for future device design.

  9. 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.

  10. Back-gated Nb-doped MoS2 junctionless field-effect-transistors

    Directory of Open Access Journals (Sweden)

    Gioele Mirabelli

    2016-02-01

    Full Text Available Electrical measurements were carried out to measure the performance and evaluate the characteristics of MoS2 flakes doped with Niobium (Nb. The flakes were obtained by mechanical exfoliation and transferred onto 85 nm thick SiO2 oxide and a highly doped Si handle wafer. Ti/Au (5/45 nm deposited on top of the flake allowed the realization of a back-gate structure, which was analyzed structurally through Scanning Electron Microscopy (SEM and Transmission Electron Microscopy (TEM. To best of our knowledge this is the first cross-sectional TEM study of exfoliated Nb-doped MoS2 flakes. In fact to date TEM of transition-metal-dichalcogenide flakes is extremely rare in the literature, considering the recent body of work. The devices were then electrically characterized by temperature dependent Ids versus Vds and Ids versus Vbg curves. The temperature dependency of the device shows a semiconductor behavior and, the doping effect by Nb atoms introduces acceptors in the structure, with a p-type concentration 4.3 × 1019 cm−3 measured by Hall effect. The p-type doping is confirmed by all the electrical measurements, making the structure a junctionless transistor. In addition, other parameters regarding the contact resistance between the top metal and MoS2 are extracted thanks to a simple Transfer Length Method (TLM structure, showing a promising contact resistivity of 1.05 × 10−7 Ω/cm2 and a sheet resistance of 2.36 × 102 Ω/sq.

  11. Nb-doped rutile TiO2 mesocrystals with enhanced lithium storage properties for lithium ion battery.

    Science.gov (United States)

    Wei, Mingdeng; Lin, Tongbin; Zhang, Weifeng; Wu, Nae-Lih

    2017-02-22

    A homogeneous Nb-doped rutile TiO2 mesocrystal material was synthesized successfully via a facile hydrothermal route. The incorporation of Nb5+ not only promotes the crystallization for the building subunits of the rutile TiO2 mesocrystal but also improves the electrochemical performance at higher current rates. For instance, a capacity of 96.3 mA h g-1 at a current density as high as 40 C and an excellent long-term cycling stability with a capacity loss of ca. 0.006% per cycle at 5 C can be achieved when an appropriate amount of Nb5+ was doped into rutile TiO2 mesocrystal. The reason resulting in the improvement of rate capability might be attributed to the enhancement of electronic conductivity, Li-ion diffusion kinetic and surface storage property for the Nb-doped rutile TiO2 mesocrystal.

  12. 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.

  13. 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.

  14. Influence of doping on OH absorption in LiNbO{sub 3} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Choubey, R.K.; Sen, P. [Department of Applied Physics, SGSITS, Indore - 452 003 (India); Kar, S.; Ramshankar, P. [Advanced Materials Division, Korea Research Institute of Chemical Technology, Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejoen (Korea); Bartwal, K.S. [Advanced Materials Division, Korea Research Institute of Chemical Technology, Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejoen (Korea); Laser Materials Development and Devices Division, Raja Ramanna Centre for Advanced Technology, Indore - 452 013 (India); Khattak, B.Q.

    2007-07-15

    Undoped, Cr doped and Mg, Cr codoped LiNbO{sub 3} crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV-Visible spectroscopy. Infrared optical absorption for OH{sup -} ion has been used to study the effect of dopants on the crystals. The peak position of OH{sup -} shift to 3535 cm{sup -1} for Mg, Cr codoped crystals compared to 3484 cm{sup -1}for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm{sup -1}) and 653 nm (15313 cm {sup -1}) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm{sup -1}) and 678 nm (14749 cm{sup -1}). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO{sub 3} crystals. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Defect-induced ferromagnetism in crystalline SrTiO3

    Energy Technology Data Exchange (ETDEWEB)

    Osten, Julia; Potzger, Kay; Shalimov, Artem; Talut, Georg; Reuther, Helfried; Arpaci, Seda; Buerger, Danilo; Schmidt, Heidemarie [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden (Germany); Levin, Alexander.A. [Institut fuer Strukturphysik, Technische Universitaet Dresden, 01062 (Germany); Nestler, Tina; Meyer, Dirk C. [Institut fuer Experimentelle Physik, Technische Universitaet Bergakademie Freiberg, 09596 Freiberg (Germany)

    2011-07-01

    Ion irradiation of high-quality SrTiO3 single crystals leads to room-temperature ferromagnetism. Structural analysis revealed oxygen deficient (polycrystalline) SrTiO3, Sr2Ti6O13, or Ruddlesden-Popper like secondary phases at the sample surface induced by the irradiation. The lack of potentially ferromagnetic secondary phases suggests defects to be the origin of the observed ferromagnetic signal.

  16. 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...

  17. Structure,Electrical,and Optical Properties of Nb-doped BaTiO3 Thin Films Grown by Laser Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    GUO Hai-Zhong; LIU Li-Feng; LU Hui-Bin; FEI Yi-Yan; XIANG Wen-Feng; ZHOU Yue-Liang; CHEN Zheng-Hao

    2004-01-01

    @@ Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.

  18. Dual Band Electrochromic Devices Based on Nb-Doped TiO2 Nanocrystalline Electrodes.

    Science.gov (United States)

    Barawi, Mariam; De Trizio, Luca; Giannuzzi, Roberto; Veramonti, Giulia; Manna, Liberato; Manca, Michele

    2017-04-25

    The reliable exploitation of localized surface plasmon resonance in transparent conductive oxides is being pursued to push the developement of an emerging class of advanced dynamic windows, which offer the opportunity to selectively and dynamically control the intensity of the incoming thermal radiation without affecting visible transparency. In this view, Nb-doped TiO2 colloidal nanocrystals are particularly promising, as they have a wide band gap and their plasmonic features can be finely tailored across the near-infrared region by varying the concentration of dopants. Four batches of Nb-doped TiO2 nanocrystals with different doping levels (from 0% to 15% of niobium content) have been used here to prepare highly transparent mesoporous electrodes for near-infrared selective electrochromic devices, capable of dynamically modulating the intensity of the transmitted radiation upon the application of a relatively small bias voltage. An engineered dual band electrochromic device (made of 10%-Nb-doped TiO2 nanocrystals) has been eventually fabricated. It was shown to provide two complementary spectroelectrochemical responses, which can be independently controlled through the intensity of the applied potential: a large variation of the optical transmittance in the near-infrared region (by the intensification of the localized surface plasmon scattering) was achievable in the 0-3 V voltage window, reaching values greater than 64% in the spectral range from 800 to 2000 nm, whereas the visible absorption could also be intensively varied at higher potentials (from 3 to 4 V), driven by Li intercalation into the TiO2 anatase lattice.

  19. Transport properties of a quasi-two-dimensional electron system formed in LaAlO3/EuTiO3/SrTiO3 heterostructures

    Science.gov (United States)

    De Luca, G. M.; Di Capua, R.; Di Gennaro, E.; Granozio, F. Miletto; Stornaiuolo, D.; Salluzzo, M.; Gadaleta, A.; Pallecchi, I.; Marrè, D.; Piamonteze, C.; Radovic, M.; Ristic, Z.; Rusponi, S.

    2014-06-01

    We study the structural, magnetic, and transport properties of LaAlO3/EuTiO3/SrTiO3 heterostructures grown by pulsed laser deposition. The samples are characterized in situ by electron diffraction and scanning probe microscopy and ex situ by transport measurements and x-ray absorption spectroscopy. LaAlO3/EuTiO3/SrTiO3 films show a ferromagnetic transition at T ≤7.5 K, related to the ordering of Eu2+ spins, even in samples characterized by just two EuTiO3 unit cells. A finite metallic conductivity is observed only in the case of samples composed by one or two EuTiO3 unit cells and, simultaneously, by a LaAlO3 thickness greater than or equal to four unit cells. The effect of ferromagnetic EuTiO3 on the transport properties of δ-doped LaAlO3/EuTiO3/SrTiO3 is critically discussed.

  20. 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.

  1. Ferroelectric domain of epitaxial AgNbO3 thin film

    Science.gov (United States)

    Ahn, Yoonho; Seo, Jeongdae; Lee, Kwang Jo; Son, Jong Yeog

    2016-03-01

    We investigated ferroelectric properties of silver niobate (AgNbO3) thin film grown on Nb-doped SrTiO3 substrate by pulsed laser deposition. The AgNbO3 thin film exhibited room temperature ferroelectricity with a large remanent polarization of about 31 μC/cm2 (2Pr~62 μC/cm2) and fast switching behavior within 120 ns. Triangular grains of AgNbO3 thin film were observed by atomic force microscopy (AFM). The piezoelectric force microscopy (PFM) study revealed that the AgNbO3 thin film had mosaic-like ferroelectric domain structure. In comparison with PbTiO3 thin films, domain size of the AgNbO3 thin films was smaller than that of PbTiO3 thin films. Based on Landau, Lifshitz, and Kittel (LLK) scaling law of the domain size versus film thickness curves, it is inferred that AgNbO3 thin films have slightly lower domain wall energy than that of PbTiO3 thin films.

  2. Photoionization energies of Cr{sup 3+}-doped LiNbO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Happek, U. [Department of Physics and Astronomy, University of Georgia, Athens, GA 30605 (United States)]. E-mail: uhappek@physast.uga.edu; Salley, G.M. [Department of Physics, Wofford College, Spartanburg, SC 29303 (United States)

    2007-07-15

    We report on a study of intra-ion and electron transfer transitions in Cr{sup 3+}-doped LiNbO{sub 3}. The energies of the meta-stable emitting levels of Cr{sup 3+} on both Li and the Nb sites are determined by standard optical spectroscopy techniques. Photoconductive measurements are used to determine the ionization energies of both species of Cr{sup 3+} ions. From these results, energy level diagrams are created which give the energies of the optically active levels with respect to the host valence and conduction bands. The emitting {sup 4}T{sub 2} level of Cr{sup 3+} on a Li site and on a Nb site is found to lie 1.5 and 1.2 eV below the conduction band bottom, respectively. These results lead to the suggestion that the lack of laser action found in LiNbO{sub 3}:Cr{sup 3+} may be due to strong excited state absorption transitions from the meta-stable {sup 4}T{sub 2} level to the host conduction band.

  3. Nanostructured TiO2 Doped with Nb as a Novel Support for PEMFC

    Directory of Open Access Journals (Sweden)

    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.

  4. Design of n - and p -type oxide thermoelectrics in LaNiO3/SrTiO3(001 ) superlattices exploiting interface polarity

    Science.gov (United States)

    Geisler, Benjamin; Blanca-Romero, Ariadna; Pentcheva, Rossitza

    2017-03-01

    We investigate the structural, electronic, transport, and thermoelectric properties of LaNiO3/SrTiO3(001 ) superlattices containing either exclusively n - or p -type interfaces or coupled interfaces of opposite polarity by using density functional theory calculations with an on-site Coulomb repulsion term. The results show that significant octahedral tilts are induced in the SrTiO3 part of the superlattice. Moreover, the La-Sr distances and Ni-O out-of-plane bond lengths at the interfaces exhibit a distinct variation by about 7 % with the sign of the electrostatic doping. In contrast to the much studied LaAlO3/SrTiO3 system, the charge mismatch at the interfaces is exclusively accommodated within the LaNiO3 layers, whereas the interface polarity leads to a band offset and to the formation of an electric field within the coupled superlattice. Features of the electronic structure indicate an orbital-selective quantization of quantum well states. The potential- and confinement-induced multiband splitting results in complex cylindrical Fermi surfaces with a tendency towards nesting that depends on the interface polarity. The analysis of the thermoelectric response reveals a particularly large positive Seebeck coefficient (135 μ V /K) and a high figure of merit (0.35) for room-temperature cross-plane transport in the p -type superlattice that is attributed to the participation of the SrTiO3 valence band. Superlattices with either n - or p -type interfaces show cross-plane Seebeck coefficients of opposite sign and thus emerge as a platform to construct an oxide-based thermoelectric generator with structurally and electronically compatible n - and p -type oxide thermoelectrics.

  5. Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001)

    Science.gov (United States)

    Lobacheva, O.; Yiu, Y. M.; Chen, N.; Sham, T. K.; Goncharova, L. V.

    2017-01-01

    Local surface structure of single crystal strontium titanate SrTiO3 (001) samples implanted with Fe in the range of concentrations between 2 × 1014 to 2 × 1016 Fe/cm2 at 30 keV has been investigated. In order to facilitate Fe substitution (doping), implanted samples were annealed in oxygen at 350 °C. Sr depletion was observed from the near-surface layers impacted by the ion-implantation process, as revealed by Rutherford Backscattering Spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), X-ray Absorption Near Edge Spectroscopy (XANES), and Atomic Force Microscopy (AFM). Hydrocarbon contaminations on the surface may contribute to the mechanisms of Sr depletion, which have important implications for Sr(Ti1-xFex)O3-δ materials in gas sensing applications.

  6. Fabricating superconducting interfaces between artificially grown LaAlO3 and SrTiO3 thin films

    Directory of Open Access Journals (Sweden)

    Danfeng Li

    2014-01-01

    Full Text Available Realization of a fully metallic two-dimensional electron gas (2DEG at the interface between artificially grown LaAlO3 and SrTiO3 thin films has been an exciting challenge. Here we present for the first time the successful realization of a superconducting 2DEG at interfaces between artificially grown LaAlO3 and SrTiO3 thin films. Our results highlight the importance of two factors—the growth temperature and the SrTiO3 termination. We use local friction force microscopy and transport measurements to determine that in normal growth conditions the absence of a robust metallic state at low temperature in the artificially grown LaAlO3/SrTiO3 interface is due to the nanoscale SrO segregation occurring on the SrTiO3 film surface during the growth and the associated defects in the SrTiO3 film. By adopting an extremely high SrTiO3 growth temperature, we demonstrate a way to realize metallic, down to the lowest temperature, and superconducting 2DEG at interfaces between LaAlO3 layers and artificially grown SrTiO3 thin films. This study paves the way to the realization of functional LaAlO3/SrTiO3 superlattices and/or artificial LaAlO3/SrTiO3 interfaces on other substrates.

  7. Nb-doped TiO2 thin films as photocatalytic materials

    Indian Academy of Sciences (India)

    Catalin Adomnitei; Sorin Tascu; Dumitru Luca; Marius Dobromir; Mihaela Girtan; Diana Mardare

    2015-09-01

    Amorphous undoped and Nb-doped films were obtained by the spin coating method. The films have a compact structure, as revealed by scanning electron microscopy, and are very thin, with thickness values under 100 nm. The photocatalytic activity of the films was evaluated by observing the decomposition of an oleic acid solution under UV irradiation, and by studying the change in the optical transmittance of an aqueous solution containing methylene blue, in the presence of the UV-irradiated films. More than 30 h, depending on doping, are needed to recover their initial contact angles before applying oleic acid. The increase of the optical transmittance of the methylene blue solution confirms the photocatalytic degradation of methylene blue on the Nb-doped TiO2 films. X-ray photoelectron spectroscopy studies, performed to detect the presence of the carbon on the irradiated surface of the films, drive to the conclusion that at the surface of the films, even for contact angles close to 0°, the presence of carbon still can be detected, which demonstrates that hydrophilicity is ruled by a different mechanism than photocatalysis.

  8. Atomic structures and electronic properties of 2H-NbSe{sub 2}: The impact of Ti doping

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hongping, E-mail: hpli@mail.ujs.edu.cn, E-mail: zcwang@wpi-aimr.tohoku.ac.jp; Chen, Lin; Zhang, Kun; Liang, Jiaqing; Tang, Hua; Li, Changsheng [Institute for Advanced Materials, School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Liu, Xiaojuan; Meng, Jian [State Key Laboratory of Rare Earth Resources Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Wang, Zhongchang, E-mail: hpli@mail.ujs.edu.cn, E-mail: zcwang@wpi-aimr.tohoku.ac.jp [Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2014-09-14

    Layered transition metal dichalcogenides have aroused renewed interest as electronic materials, yet their electronic performances could be modified by chemical doping. Here, we perform a systematic first-principles calculation to investigate the effect of Ti doping on atomic structure and electronic properties of the 2H-NbSe{sub 2}. We consider a total of three possible Ti-doping models and find that both the substitution and intercalated models are chemically preferred with the intercalation model being more favorable than the substitution one. Structural analyses reveal a slight lattice distortion triggered by Ti doping, but the original structure of 2H-NbSe{sub 2} is maintained. We also observe an expansion of c axis in the substituted model, which is attributed to the reduced van der Waals interaction arising from the increased Se-Se bond length. Our calculations also predict that the electron transport properties can be enhanced by the Ti doping, especially for the Ti-intercalated 2H-NbSe{sub 2}, which should be beneficial for the realization of superconductivity. Furthermore, the covalence element is found in the Ti-Se bonds, which is ascribed to the hybridization of Ti 3d and Se 4p orbitals. The findings indicate that doping of transition metals can be regarded as a useful way to tailor electronic states so as to improve electron transport properties of 2H-NbSe{sub 2}.

  9. Creation of domains by direct electron beam writing in magnesium-doped LiNbO{sub 3} and LiNbO{sub 3}:Fe single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Palatnikov, M.N. [Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, 26a Akademgorodok, Apatity, Murmansk 184209 (Russian Federation); Kokhanchik, L.S.; Emelin, E.V. [Institute of Microelectronics Technology and High Purity Materials of Russian Academy of Sciences, 6 Academician Ossipyan st, Chernogolovka, Moscow 142432 (Russian Federation); Sidorov, N.V. [Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, 26a Akademgorodok, Apatity, Murmansk 184209 (Russian Federation); Manukovskaya, D.V., E-mail: deenka@yandex.ru [Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, 26a Akademgorodok, Apatity, Murmansk 184209 (Russian Federation)

    2016-03-01

    Highlights: • The periodic domains are created in crystal LiNbO{sub 3}:Mg by direct electron beam writing. • Periodic domains appear only at equilibrium between switching and screening times. • Equilibrium exists in crystal co-doped by Fe. • Shape and appearance of domains depend on the conductivity type. - Abstract: Domain structures in the Z-cut of highly doped LiNbO{sub 3}:Mg and LiNbO{sub 3}:Mg,Fe single crystals were created by direct electron beam writing (DEBW). It was found that the value and type of electron conductivity influence the shape and number of domains thus created. Controlled electron beam regular domains were created only in samples of the crystal LiNbO{sub 3}:Mg,Fe [MgO] = 5.16 mol.%, [Fe] = 0.007 mol.%. In highly doped LiNbO{sub 3}:Mg ([MgO] = 5.19 mol.%) crystal, the domains were formed chaotically and controlled creation of domains did not occur. The domain shapes were analyzed in the framework of the theory of screening of domain nuclei depolarizing electric fields and the influence of screening on the final shape of domains. It was found that screening of intrinsic electric fields is faster in the LiNbO{sub 3}:Mg,Fe crystal. This crystal has a high electronic conductivity of hopping type with a high mobility of charge carriers. Thus, a small amount of Fe provides equilibrium between the ferroelectric switching velocity and screening of the depolarizing electric field velocity. The results are discussed considering differences in the electron conductivity mechanisms, which control the screening of depolarizing electric field velocity and spatial charge area formed under an electron beam.

  10. Symmetry and structure of SrTiO3 nanotubes

    Science.gov (United States)

    Evarestov, Robert

    2011-06-01

    The full study of perovskite type nanotubes with square morphology is given for the first time. The line symmetry group L = ZP (a product of one axial point group P and one infinite cyclic group Z of generalized translations) of single-walled (SW) and double-walled (DW) SrTiO3 nanotubes (NT) is considered. The nanotube is defined by the square lattice translation vector L = l1a + l2b and chiral vector R = n1a + n2b, (l1, l2, n1 and n2 are integers). The nanotube of the chirality (n1,n2) is obtained by folding the (001) slabs of two- layers (with the layer group P4mm) and of three layers (with the layer group P4/mmm) in a way that the chiral vector R becomes circumference of the nanotube. Due to the orthogonality relation (RL) = 0, l1/l2 = -n2/n1 i.e. SW nanotubes with square morphology are commensurate for any rolling vector R(n1,n2). For SW (n,0) NTs the line symmetry groups belong to family 11 (T^Dnh) and are n/mmm or for even and odd n, respectively. For SW (n,n) NTs the line symmetry groups (2n)n/mcm belong to family 13 (T2n1 Dnh). The line symmetry group of a double-wall nanotube is found as intersection L2 = Z2P2 = (L ∩ L') of the symmetry groups L and L' of its single-wall constituents as earlier considered for DW CNTs. The symmetry group of DWNT (n,0)@M(n,0) belongs to the same family 11 (T^Dnh) as its SW constituents. The symmetry group of DWNT (n,n)@M(n,n) depends on the parity of M. For DW NTs with odd M, the line symmetry groups are the same as for their SW constituents and belong to family 13 (T2n1 Dnh). For even M, the rotations about screw axis of order 2n are changed by rotations around pure rotation axis of order n so that DW NT line symmetry groups belong to family 11 (T^Dnh). Commensurate STO DWNTs (n1,0)@(n2,0) and (n1, n1)@(n2, n2) belong to family 11 (T^Dnh) with n equal to the greatest common divisor of n1 and n2.

  11. Effects of Nb-doped on the structure and electrochemical performance of LiFePO{sub 4}/C composites

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Zhipeng [Hebei Key Laboratory of Applied Chemistry, College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China); Shao, Guangjie, E-mail: shaoguangjie@ysu.edu.cn [Hebei Key Laboratory of Applied Chemistry, College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China); State Key Laboratory of Metastable Materials Science and Technology, Qinhuangdao 066004 (China); Wang, Guiling; Zhang, Ying; Du, Jianping [Hebei Key Laboratory of Applied Chemistry, College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2014-02-15

    The olivine-type niobium doping Li{sub 1−x}Nb{sub x}FePO{sub 4}/C (x=0, 0.005, 0.010, 0.015, 0.025) cathode materials were synthesized via a two-step ball milling solid state reaction. The effects of Nb doping were charactered by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and galvanostatic charge–discharge. It is found that Nb doping enlarges the interplanar distance of crystal plane parallel to [0 1 0] direction in LiFePO{sub 4}. In other words, it widens the one dimensional diffusion channels of Li{sup +} along the [0 1 0] direction. Electrochemical test results indicate that the Li{sub 0.99}Nb{sub 0.01}FePO{sub 4}/C composite exhibits the best electrochemical performance with initial special discharge capacity of 139.3 mA h g{sup −1} at 1 C rate. The present synthesis route is promising in making the solid state reaction method more practical for preparation of the LiFePO{sub 4} material. - Graphical abstract: The proper amount of Nb doping widens the one dimensional diffusion channels of Li{sup +} along the [0 1 0] direction. Display Omitted - Highlights: • The Nb doping LiFePO{sub 4}/C is prepared by a facile two-step ball milling solid state reaction. • The sample possesses the better high-rate performance. • The tap density of Li{sub 0.99}Nb{sub 0.01}FePO{sub 4}/C sample is 1.76 g cm{sup −3}.

  12. Effect of Crystal Growth Direction on Domain Structure of Mn-Doped (Na,K)NbO3 Crystal

    Science.gov (United States)

    Tsuchida, Kohei; Kakimoto, Ken-ichi; Kagomiya, Isao

    2013-09-01

    Single crystals of (Na0.55K0.45)(Nb0.995Mn0.005)O3 have been grown by a floating zone method in N2 and decompression atmosphere to avoid alkaline metal volatilization on the SrTiO3 material base. The variation of their ferroelectric domain structure and the chemical composition of the grown crystal in the growth direction were evaluated. In the crystal grown in N2 atmosphere, the Na and K are not distributed homogeneously. In addition, the phase transition temperature TC and TO-T showed different values between the grown crystal and raw material. By using laser scanning confocal microscope, the domain structures of the grown crystal revealed random patterns in the initial growth stage and lamellar patterns in the progressing crystal growth. In decompression atmosphere, the TC and TO-T values of the grown crystal were similar to those of the raw material and the domain structures showed a constant domain size. The electrical property of the crystal became stable and the domain structure was easily switched against applied electrical field because the oriented lamellar domain was created during cooling of the crystal.

  13. Tuning the carrier density of LaAlO3/SrTiO3 interfaces by capping La1-xSrxMnO3

    Science.gov (United States)

    Shi, Y. J.; Wang, S.; Zhou, Y.; Ding, H. F.; Wu, D.

    2013-02-01

    We present a systematical study on the electronic transport properties of the insulating LaAlO3 (3 unit cells)/SrTiO3 interfaces capping with thin layers of La1-xSrxMnO3, whose formal polarization is continually tuned by Sr doping. When the Sr doping is lower than 2/3, the LaAlO3/SrTiO3 interfaces show metallic behaviors. The carrier mobility is almost independent on the Sr doping for metallic interface, indicating that the capping layer does not change the density of the oxygen vacancies and the interface intermixing. However, the sheet carrier densities monotonically decrease as increasing Sr doping, which is ascribed to the decrease of the La1-xSrxMnO3 formal polarization. These results strongly support the intrinsic mechanism of the polar catastrophe model and provide a new approach to tailor the interface states of complex oxide heterostructures.

  14. Effects of Nb2O5 on thermal stability and optical properties of Er3+-doped tellurite glasses

    Institute of Scientific and Technical Information of China (English)

    Zhao Chun; Zhang Qin-Yuan; Pan Yue-Xiao; Jiang Zhong-Hong

    2006-01-01

    Er3+-doped tellurite glasses with molar compositions of xNb2O5 - (14.7 - x)Na2O-10ZnO-SK2O-10GeO2-60TeO2-0.3Er2O3 (x = 0, 3, 5, 7 and 9) have been investigated for developing 1.5 μm fibre and planar amplifiers. The effects of Nb2O5 on the thermal stability and optical properties of Er3+-doped tellurite glasses have been discussed.It is noted that the incorporation of Nb2O5 (x=5) increases the thermal stability of tellurite glasses significantly.Er3+-doped niobium tellurite glasses exhibit a large stimulated emission cross-section (7.2×10-21 - 10.7×10-21 cm2)and the gain bandwidth, FWHM×σepeak (274×10-28 -480×10-28 cm3), which are significantly higher than that of silicate and phosphate glasses. In addition, the intensity of upconversion luminescence of the Er3+-doped niobium tellurite glasses decreases rapidly with increasing Nb2O5 content. As a result, Er3+-doped niobium tellurite glasses might be a potential candidate for developing laser or optical amplifier devices.

  15. Structural characterization of niobium oxide thin films grown on SrTiO3 (111) and (La,Sr)(Al,Ta)O3 (111) substrates

    Science.gov (United States)

    Dhamdhere, Ajit R.; Hadamek, Tobias; Posadas, Agham B.; Demkov, Alexander A.; Smith, David J.

    2016-12-01

    Niobium oxide thin films have been grown by molecular beam epitaxy on SrTiO3 (STO) (111) and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT) (111) substrates. Transmission electron microscopy (TEM) confirmed the formation of high quality films with coherent interfaces. Films grown with higher oxygen pressure on STO (111) resulted in a (110)-oriented NbO2 phase with a distorted rutile structure, which can be described as body-centered tetragonal. The a lattice parameter of NbO2 was determined to be ˜13.8 Å in good agreement with neutron diffraction results published in the literature. Films grown on LSAT (111) at lower oxygen pressure produced the NbO phase with a defective rock salt cubic structure. The NbO lattice parameter was determined to be a ≈ 4.26 Å. The film phase/structure identification from TEM was in good agreement with in situ x-ray photoelectron spectroscopy measurements that confirmed the dioxide and monoxide phases, respectively. The atomic structure of the NbO2/STO and NbO/LSAT interfaces was determined based on comparisons between high-resolution electron micrographs and image simulations.

  16. 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.)

  17. 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).

  18. DFT-based Theoretical Calculation of Nb- and W-doped Anatase TiO2

    Science.gov (United States)

    Suenaga, Takahiro; Kamisaka, Hideyuki; Nakamura, Hisao; Yamashita, Koichi

    2010-03-01

    The structure and electronic states in the Nb-doped TiO2 (TNO) and W-doped TiO2 (TWO) in anatase phase were investigated from the first-principle using DFT-based band structure method. In addition to the cases where the dopant substituting a Ti atom, cells containing a dopant (MTi; M = Nb, W) and an oxygen vacancy (VO) were calculated in order to clarify the role of the oxygen vacancy in the system. Furthermore, cells containing two dopants and an oxygen vacancy (2MTi--VO), and cells with a dopant and two oxygen vacancies (MTi--2VO) were calculated. Energetically stable structures were found among the sampled 2WTi--VO and WTi--2VO cells, while the corresponding structures in TNO did not show any significant energy stabilization. Impurity states were found in the stable 2WTi--VO and WTi--2VO structures, and an approach of the two WTi atoms was observed in the former. The present results rationalize the lower electronic conductivity of TWO than that of TNO, and suggest possible formation of complex structures consisting of the WTi dopants and the oxygen vacancies.

  19. The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices

    Institute of Scientific and Technical Information of China (English)

    Zhu Zhen-Ye; Wang Biao; Wang Hai; Zheng Yue; Li Qing-Kun

    2007-01-01

    We have performed the first-principles calculation to investigate the origins of ferroelectricities and different polarization behaviours of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3- The density of state (DOS) and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO3/rTiO3 and PbTiO3/SrTiO3. Owing to the decline of internal electric field in SrTiO3 (ST) layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO3 in the superlattices. We find that the polarization of PbTiO3/SrTiO3 is largerthan that of BaTiO3/SrTiO3 at the same ratio of components, because the polarization mismatch between PbTiO3 and SrTiO3 is larger than that between BaTiO3 and SrTiO3. The polarization and tetragonality are enhanced with respect to those of bulk tetragonal BaTiO3 in the superlattices BaTiO3/SrTiO3, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO3 in superlattices PbTiO3/SrTiO3.

  20. Scalable Preparation of SrTiO3 Submicro-wires from Layered Titanate Nanowires

    Institute of Scientific and Technical Information of China (English)

    TANG Mao-yu; JI Tian-hao; XIE Jian

    2007-01-01

    SrTiO3 submicro-wires were prepared by the reaction of layered titanate nanowires with Sr(OH)2 powder in an autoclave. The wires were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM),Ultra-violet visible (UV-vis), photoluminescence (PL) and Raman spectroscopy. The XRD measurement shows that the prepared SrTiO3 submicro-wires hardly have impurity phases. The SEM and TEM images demonstrate that the scalable wires, which need to be processed at the reaction temperature of 180 ℃ for about 48 hours, are not composed of single crystals. The PL shows that the wire-like SrTiO3 has emission peaks at the wavelengths of 568 and 585 nm. Further, the Raman spectroscopy reveals structural changes in the products through different reaction time.

  1. Preparation, characterization and photocatalytic activities of TiO2-SrTiO3 composites

    Science.gov (United States)

    Wang, Yan; Zhu, Lianjie; Gao, Fubo; Xie, Hanjie

    2017-01-01

    Series of TiO2-SrTiO3 composites were synthesized by hydrothermal method, using TiO2 nanotube array as a precursor and Sr(OH)2 as a Sr source material. TiO2-SrTiO3 products with various composition were obtained by simply changing the reaction time. The as-synthesized products were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical properties were studied by means of UV-Vis absorption spectroscopy and photoluminescence (PL) spectra. Their photocatalytic activities were assessed by photodegradation of rhodamine B (RhB) solution and the photocatalytic reaction mechanism was discussed. The TiO2-SrTiO3 composites obtained at 2 h exhibits the highest activity for photodegradation of RhB.

  2. Relation between structural instabilities in EuTiO3 and SrTiO3

    Science.gov (United States)

    Bussmann-Holder, A.; Köhler, J.; Kremer, R. K.; Law, J. M.

    2011-06-01

    Specific heat measurements and theoretical calculations reveal an intimate analogy between EuTiO3 and SrTiO3. For EuTiO3, a hitherto unknown specific heat anomaly is discovered at temperatures TA= 282(1)K, which is analogous to the well-known specific heat anomaly of SrTiO3 at the temperature TA= 105K caused by an antiferrodistortive transition. Because the zone center soft phonon mode observed in both systems can be modeled with the same parameters, we ascribe the new 282(1)K instability of EuTiO3 to an antiferrodistortive phase transition. The higher transition temperature of EuTiO3 as compared to SrTiO3 results from spin-phonon coupling.

  3. Transport in ferromagnetic GdTiO3/SrTiO3 heterostructures

    Science.gov (United States)

    Moetakef, Pouya; Zhang, Jack Y.; Kozhanov, Alexander; Jalan, Bharat; Seshadri, Ram; Allen, S. James; Stemmer, Susanne

    2011-03-01

    Epitaxial GdTiO3/SrTiO3 structures with different SrTiO3 layer thicknesses are grown on (001) (LaAlO3)0.3(Sr2AlTaO6)0.7 substrate surfaces by hybrid molecular beam epitaxy. It is shown that the formation of the pyrochlore (Gd2Ti2O7) phase can be avoided if GdTiO3 is grown by shuttered growth, supplying alternating monolayer doses of Gd and of the metalorganic precursor that supplies both Ti and O. Phase-pure GdTiO3 films grown by this approach exhibit magnetic ordering with a Curie temperature of 30 K. The electrical transport characteristics can be understood as being dominated by a conductive interface layer within the SrTiO3.

  4. 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.

  5. 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.

  6. Thermal, defects, mechanical and spectral properties of Nd-doped GdNbO4 laser crystal

    Science.gov (United States)

    Ding, Shoujun; Zhang, Qingli; Luo, Jianqiao; Liu, Wenpeng; Wang, Xiaofei; Sun, Guihua; Li, Xiuli; Sun, Dunlu

    2017-05-01

    A Nd-doped GdNbO4 crystal was grown successfully by Czochralski method. Its monoclinic structure was determined by X-ray diffraction; the unit-cell parameters are a = 5.38 Å, b = 11.09 Å, c = 5.11 Å, and β = 94.56°. The morphological defects of Nd:GdNbO4 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:GdNbO4 were investigated first. Thermal properties of Nd:GdNbO4, including thermal expansion coefficient and specific heat, were measured along a-, b-, and c-crystalline axes. Thermal properties indicate that the Nd:GdNbO4 pumped along c-axis can reduce the thermal lensing effect effectively. The specific heat is 0.53 J g-1 K-1 at 300 K, indicating a relatively high damage threshold of Nd:GdNbO4. The transmission and emission spectrum of Nd:GdNbO4 were measured, and the absorption peaks were assigned. The strongest emission peak of Nd:GdNbO4 is located at 1065.3 nm in the spectral range of 850-1420 nm excited by 808 nm laser. The refractive index of Nd:GdNbO4 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:GdNbO4.

  7. Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

    Directory of Open Access Journals (Sweden)

    J. A. Tilka

    2016-12-01

    Full Text Available The creation of thin SrTiO3 crystals from (001-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001 plane. Synchrotron x-ray nanodiffraction rocking curve widths of these SrTiO3 sheets are less than 0.02°, less than a factor of two larger than bulk SrTiO3, making these crystals suitable substrates for epitaxial thin film growth. The change in the rocking curve width is sufficiently small that we deduce that dislocations are not introduced into the SrTiO3 sheets. Observed lattice distortions are consistent with a low concentration of point defects.

  8. Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

    Science.gov (United States)

    Tilka, J. A.; Park, J.; Sampson, K. C.; Cai, Z.; Evans, P. G.

    2016-12-01

    The creation of thin SrTiO3 crystals from (001)-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001) plane. Synchrotron x-ray nanodiffraction rocking curve widths of these SrTiO3 sheets are less than 0.02°, less than a factor of two larger than bulk SrTiO3, making these crystals suitable substrates for epitaxial thin film growth. The change in the rocking curve width is sufficiently small that we deduce that dislocations are not introduced into the SrTiO3 sheets. Observed lattice distortions are consistent with a low concentration of point defects.

  9. Charge modulated interfacial conductivity in SrTiO3-based oxide heterostructures

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Stamate, Eugen; Pryds, Nini;

    2011-01-01

    When depositing amorphous SrTiO3 (STO) films on crystalline STO substrates by pulsed laser deposition, metallic interfaces are observed, though both materials are band-gap insulators. The interfacial conductivity exhibits strong dependence on oxygen pressure during film growth, which is closely...

  10. 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 t

  11. 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...

  12. Growing LaAlO3/SrTiO3 interfaces by sputter deposition

    NARCIS (Netherlands)

    Dildar, I.M.; Neklyudova, M.; Xu, Q.; Zandbergen, H.W.; Harkema, S.; Boltje, D.; Aarts, J.

    2015-01-01

    Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showe

  13. Study on the Thermal and Dielectric Properties of SrTiO3/Epoxy Nanocomposites

    Directory of Open Access Journals (Sweden)

    Xiaoxing Zhang

    2017-05-01

    Full Text Available SrTiO3/epoxy nanocomposites are prepared using the facile solution-processing technique by incorporating SrTiO3 nanoparticles with different weight fractions into the epoxy resin host. The morphology of the nanoparticles and composites, as well as the thermal conduction characteristics and electrical properties of the composites were investigated via conventional testing methods. The thermal conductivity increased along with the SrTiO3 weight fractions, and the thermal conductivity of the SrTiO3/epoxy composite with 40 wt % weight fraction increased to 0.52 W/mK. The dielectric constant increased along with the weight fractions and decreased along with frequency, thereby suggesting that the interfacial and dipole polarization do not follow the changes in the electrical field direction at high frequency. The dielectric constants at 1 kHz frequency increased along with temperature. Surface breakdown tests illustrated further improvements in the thermal and electrical properties of the composites. In the same time span of 40 s, the 40 wt % nanocomposite demonstrated a rapid temperature decline rate of 6.77 °C/s, which was 47% faster than that of the pure epoxy sample. The surface breakdown voltage also increased along with the weight fractions. The functional composites can solve the key problem in the intelligentization, miniaturization, and high-efficiency of the gas-insulated switchgear, which warrants further research.

  14. 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...

  15. Pulsed laser deposition-induced reduction of SrTiO3 crystals

    NARCIS (Netherlands)

    Scullin, Matthew L.; Ravichandran, Jayakanth; Yu, Choongho; Huijben, Mark; Seidel, Jan; Majumdar, Arun; Ramesh, R.; Ramesh, R.

    2010-01-01

    We report a generic method for fast and efficient reduction of strontium titanate (SrTiO3, STO) single crystals by pulsed laser deposition (PLD) of thin-films. The reduction was largely independent of the thin-film material deposited on the crystals. It is shown that thermodynamic conditions (450 °C

  16. Upper limit to magnetism in LaAlO3/SrTiO3 heterostructures

    NARCIS (Netherlands)

    Fitzsimmons, M.R.; Hengartner, N.W.; Singh, S.; Zhernenkov, M.; Bruno, F.Y.; Santamaria, J.; Brinkman, Alexander; Huijben, Mark; Molegraaf, Hajo; de la Venta, J.; Schuller, Ivan K.

    2011-01-01

    Using polarized neutron reflectometry we measured the neutron spin-dependent reflectivity from four LaAlO3/SrTiO3 superlattices. Our results imply that the upper limit for the magnetization averaged over the lateral dimensions of the sample induced by an 11 T magnetic field at 1.7 K is less than 2 G

  17. Enhanced Electrorheological Performance of Nb-Doped TiO2 Microspheres Based Suspensions and Their Behavior Characteristics in Low-Frequency Dielectric Spectroscopy.

    Science.gov (United States)

    Guo, Xiaosong; Chen, Yulu; Su, Ming; Li, Dong; Li, Guicun; Li, Chengdong; Tian, Yu; Hao, Chuncheng; Lei, Qingquan

    2015-12-09

    Titanium dioxide and Nb-doped titanium dioxide microspheres with the same size were fabricated by a simple sol-gel method, and the formation mechanism of Nb-doped titanium dioxide microspheres was proposed. Titanium dioxide and Nb-doped titanium dioxide microspheres were adopted as dispersed materials for electrorheological (ER) fluids to investigate the influence of the charge increase introduced by Nb doping on the ER activity. The results showed that Nb doping could effectively enhance the ER performance. Combining with the analysis of dielectric spectroscopy, it was found that the interface polarization of Nb-doped TiO2 ER fluid was larger than that of TiO2 ER fluid, which might be caused by more surface charges in Nb-TiO2 microspheres due to Nb(5+) doping and resulting in enhancement of electric field force and strengthening of fibrous structure. In addition, by comparing and analyzing the permittivity curves of Nb-TiO2/LDPE solid composite and Nb-TiO2/silicone-oil fluid composite, it could be concluded that the enhancement of permittivity at low frequency resulted from the increase of the order degree of dispersed particles in ER fluid rather than from the quasi-dc (QDC) behavior. Moreover, the absolute value of slope of permittivity curves (K) at 0.01 Hz could be utilized as the standard for judging the ability to maintain the chainlike structure. The relationships between polarizability of dispersed particles, dielectric spectrum, parameter K, and ER properties were discussed in detail.

  18. 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)

  19. Control of the Crystalline Structure and Piezoelectric Properties of (K,Na,Li)(Nb,Ta,Sb)O3 Ceramics through Transition Metal Oxide Doping

    Science.gov (United States)

    Rubio-Marcos, Fernando; José Romero, Juan; Francisco Fernández, José; Marchet, Pascal

    2011-10-01

    Divalent transition metal oxide doping of lead-free (K,Na,Li)(Nb,Ta,Sb)O3 piezoceramics is studied. Two different behaviors were observed independently of the doping metal: at low concentrations, the tetragonal structure is preserved, while at a high doping level, the material becomes orthorhombic. For any given doping level, a linear dependence was found between the pseudo-tetragonal lattice distortion and the ionic radii of doping ions. The ferroelectric and piezoelectric properties of the material are reduced by the doping, whereas the mechanical quality factor increases. Thus, the piezoelectric and ferroelectric properties of these lead-free piezoceramics can be easily controlled through metal oxide doping.

  20. Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO3 borosilicate glass–ceramics

    Indian Academy of Sciences (India)

    C R Gautam; D Kumar; O Parkash; Prabhakar Singh

    2013-06-01

    Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0 ≤ ≤ 1.0) with a step-wise increment of 0.10 in the glass [(PbSr1−)OTiO2]–[(2SiO2B2O3)]–[BaO.K2O].Nb2O5 (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm-1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (∼27 °C) to 1400 °C employing a heating rate of 10 °C/min to determine glass transition temperature, g and crystallization temperature, c. The melting temperature, m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. g and m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with ≤ 0.5 was found to have cubic structure similar to SrTiO3 ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.

  1. Resistive Switching Characteristics of 10-nm-Thick Amorphous HoScO x Films Doped with Nb and Zn

    Science.gov (United States)

    Wang, Sea-Fue; Hsu, Chia-Chun; Chu, Jinn P.; Liu, Yi-Xin; Chen, Liang-Wei

    2017-03-01

    In this study, 10-nm rare-earth metal-oxide (REMO) films, namely, pure HoScO x (HSO) and HoScO x doped with Nb (HSO-Nb) and Zn (HSO-Zn), were deposited to build resistive random access memory (RRAM) devices with a Pt/REMO/Pt structure using radio frequency magnetron sputtering. The results of x-ray diffraction and transmission electron microscopy showed that all as-deposited REMO films are featureless microstructures lacking long-range order. In all RRAM devices, layer structures were well adhered to each other with relatively smooth interfaces and no cracks or holes were observed. Hall measurements demonstrated n-type conduction in the as-deposited films. The addition of Nb and Zn increased carrier concentration and mobility of the HSO films and reduced electrical resistivity. The former was possibly caused by the electronic compensation of NbSc ··, thereby triggering the formation of polarons, and the latter was probably due to the increase in concentration of oxygen vacancies associated with acceptor doping. The RRAM devices revealed unipolar switching behavior characterized by a resistance ratio of more than three orders of magnitude, good endurance, and a long retention time. The switching behavior of the RRAM with amorphous HSO films was altered by the doping species. Doping with Nb and Zn decreased the forming voltage, facilitated the use of a smaller switching voltage, and increased the resistance ratio of high- and low-resistance states. The conduction mechanisms for the low resistive state and high resistive state were dominated by Ohmic conduction and trap-controlled space-charge-limited current mechanisms, respectively.

  2. Growth and physical properties of highly oriented La-doped (K,Na)NbO{sub 3} ferroelectric thin films

    Energy Technology Data Exchange (ETDEWEB)

    Vendrell, X., E-mail: xavier.vendrell@ub.edu [Departament de Química Inorgànica, Universitat de Barcelona, 08028 Barcelona (Spain); Raymond, O. [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, AP 14, Ensenada 22860, Baja California (Mexico); Ochoa, D.A.; García, J.E. [Department of Applied Physics, Universitat Politècnica de Catalunya — BarcelonaTech, 08034 Barcelona (Spain); Mestres, L. [Departament de Química Inorgànica, Universitat de Barcelona, 08028 Barcelona (Spain)

    2015-02-27

    Lead-free (K,Na)NbO{sub 3} (KNN) and La doped (K,Na)NbO{sub 3} (KNN-La) thin films are grown on SrTiO{sub 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{sub 4}Nb{sub 6}O{sub 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{sub 0.5}Na{sub 0.5})NbO{sub 3} and [(K{sub 0.5}Na{sub 0.5}){sub 0.985}La{sub 0.005}]NbO{sub 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.

  3. Enhancing Efficiency and Stability of Perovskite Solar Cells through Nb-Doping of TiO2 at Low Temperature.

    Science.gov (United States)

    Yin, Guannan; Ma, Jiaxin; Jiang, Hong; Li, Juan; Yang, Dong; Gao, Fei; Zeng, Jinghui; Liu, Zhike; Liu, Shengzhong Frank

    2017-03-20

    The conduction band energy, conductivity, mobility, and electronic trap states of electron transport layer (ETL) are very important to the efficiency and stability of a planar perovskite solar cell (PSC). However, as the most widely used ETL, TiO2 often needs to be prepared under high temperature and has unfavorable electrical properties such as low conductivity and high electronic trap states. Modifications such as elemental doping are effective methods for improving the electrical properties of TiO2 and the performance of PSCs. In this study, Nb-doped TiO2 films are prepared by a facile one-port chemical bath process at low temperature (70 °C) and applied as a high quality ETL for planar PSCs. Compared with pure TiO2, the Nb-doped TiO2 is more efficient for photogenerated electron injection and extraction, showing higher conductivity, higher mobility, and lower trap-state density. A PSC with 1% Nb-doped TiO2 yielded a power conversion efficiency of more than 19%, with about 90% of its initial efficiency remaining after storing for 1200 h in air or annealing at 80 °C for 20 h in a glovebox.

  4. 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.

  5. Green up-converted luminescence in (Er3+-Yb3+) co-doped LiNbO3 crystals

    Science.gov (United States)

    Stoffel, M.; Rinnert, H.; Kokanyan, E.; Demirkhanyan, G.; Demirkhanyan, H.; Aillerie, M.

    2016-07-01

    Er3+ doped and (Er3+-Yb3+) co-doped LiNbO3 (LN) crystals grown by the Czochralski method are investigated by photoluminescence spectroscopy. Green up-converted luminescence is observed in Er3+ doped LN crystals under 980 nm excitation. This is explained by an energy transfer between two neighboring Er3+ ions. In (Er3+, Yb3+) co-doped LN crystals, the intensity of the green up-converted luminescence can be further enhanced suggesting that Yb3+ ions also contribute to the up-conversion process. Time resolved photoluminescence measurements clearly demonstrate that an efficient energy transfer occurs between Yb3+ and Er3+ ions. A theoretical model taking into account the contribution of both Er3+-Er3+ pairs and Yb3+-Er3+ pairs is able to describe correctly the decay of the up-converted luminescence.

  6. Electronic structure and optical properties of Nb-doped Sr2TiO4 by density function theory calculation

    Institute of Scientific and Technical Information of China (English)

    Yun Jiang-Ni; Zhang Zhi-Yong

    2009-01-01

    This paper investigates the effect of Nb doping on the electronic structure and optical properties of by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory (DFT).The calculated results reveal that due to the electron doping, the Fermi level shifts into conduction bands(CBs) for Sr2NbxTi1-xO4 with x = 0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes, and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region. The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.

  7. Vibrational micro-energy harvesters utilizing Nb-doped Pb(Zr,Ti)O3 films on stainless steel substrates

    Science.gov (United States)

    Van Minh, L.; Sano, T.; Fujii, T.; Kuwano, H.

    2016-11-01

    This work presents the micromachined energy harvesters using Nb-doped Pb(Zr,Ti)O3 (PNZT) films grown directly on the stainless steel substrates (SUS430). Piezoelectric materials on metallic substrates have been attracted to practical and robust energy harvesters. Nb-doped PZT films with (001)-preferred orientation grown on SUS substrates provided excellent properties for energy harvesting - high piezoelectric coefficient (e 31 = -10.6 C/m2) and low dielectric permittivity (ɛr = 373). The PNZT-based micro-energy harvester comprising a cantilever of 1.7 mm× 5 mm × 0.05 mm and a proof mass of 3 mm× 5 mm × 47 mm achieved the normalized power density (NPD) of 2.87 mW.g-2.cm-3. It is the highest performance among the published SUS-based energy harvesters, being closer to the best Si- based energy harvesters.

  8. Synthesis and Characterization of Niobium-doped TiO2 Nanotube Arrays by Anodization of Ti-20Nb Alloys

    Institute of Scientific and Technical Information of China (English)

    Zhengchao Xu; Qi Li; Shian Gao; Jianku Shangi

    2012-01-01

    Well crystallized niobium-doped TiO; nanotube arrays (TiNbO-NT) were successfully synthesized via the anodization of titanium/niobium alloy sheets, followed with a heat treatment at 550 ℃ for 2 h. Morphology analysis results demonstrated that both the titanium/niobium alloy microstructure and the dissolution strength of electrolyte played major roles in the formation of nanotube structure. A single-phase microstructure was more favorable to the formation of uniform nanotube arrays, while modulating the dissolution strength of electrolyte was required to obtain nanotube arrays from the alloys with multi-phase microstructures. X-ray diffraction (XRD) and X-ray photoelectron (XPS) analysis results clearly demonstrated that niobium dopants (Nb^5+) were successfully doped into TiO2 anatase lattice by substituting Ti^4+ in this approach.

  9. Vertically aligned nitrogen doped (Sn,Nb)O{sub 2} nanotubes – Robust photoanodes for hydrogen generation by photoelectrochemical water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Patel, Prasad Prakash, E-mail: ppp4@pitt.edu [Department of Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Hanumantha, Prashanth Jampani [Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Velikokhatnyi, Oleg I.; Datta, Moni Kanchan [Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Center for Complex Engineered Multifunctional Materials, University of Pittsburgh, PA 15261 (United States); Gattu, Bharat [Department of Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, 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., E-mail: pkumta@pitt.edu [Department of Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, 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, Pittsburgh, PA 15261 (United States); School of Dental Medicine, University of Pittsburgh, PA 15217 (United States)

    2016-06-15

    Graphical abstract: - Highlights: • Nb and N co-doping provides excellent optoelectronic properties for SnO{sub 2} NTs. • The optoelectronic properties of doped SnO{sub 2} are studied by first principles study. • (Sn{sub 0.95}Nb{sub 0.05})O{sub 2}:N-600 NTs exhibits superior ABPE (4.1%) to date. • Excellent photoelectrochemical stability of (Sn{sub 0.95}Nb{sub 0.05})O{sub 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{sub 2} nanotubes (NTs), i.e., (Sn{sub 0.95}Nb{sub 0.05})O{sub 2}:N NTs for PEC water splitting. (Sn{sub 0.95}Nb{sub 0.05})O{sub 2} NTs was selected for co-doping with nitrogen by systematic analysis of applied bias photon-to-current efficiency of various Nb doped SnO{sub 2} (x = 0–0.1) compositions. Consequently, excellent photoelectrochemical stability and the highest efficiency of 4.1% is obtained for (Sn{sub 0.95}Nb{sub 0.05})O{sub 2}:N-600 NTs never observed for other known TiO{sub 2}, ZnO, and Fe{sub 2}O{sub 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{sub 2} semiconductor, further corroborating results of the experimental study.

  10. Phase conjugation of vector fields by degenerate four-wave mixing in a Fe-doped LiNbO₃.

    Science.gov (United States)

    Qian, Sheng-Xia; Li, Yongnan; Kong, Ling-Jun; Tu, Chenghou; Wang, Hui-Tian

    2014-08-15

    We propose a method to generate the phase-conjugate wave of the vector field by degenerate four-wave mixing in a c-cut Fe-doped LiNbO3 crystal. We demonstrate experimentally that the phase-conjugate wave of the vector field can be generated. In particular, the phase-conjugate vector field has also the peculiar function of compensating the polarization distortion, as the traditional phase-conjugate scaler field can compensate the phase distortion.

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

    KAUST Repository

    Sarath Kumar, S. R.

    2013-08-14

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

  12. Interfacial defects induced electronic property transformation at perovskite SrVO3/SrTiO3 and LaCrO3/SrTiO3 heterointerfaces.

    Science.gov (United States)

    Li, Junjie; Yin, Deqiang; Li, Qiang; Sun, Rong; Huang, Sumei; Meng, Fanzhi

    2017-03-08

    Unravelling the atomic structure and chemical species of interfacial defects is critical to understanding the origin of interfacial properties in many heterojunctions. Here, by combining advanced transmission electron microscopy, spectroscopy and first-principles calculations, we demonstrate interfacial Ti diffusion in SrVO3/SrTiO3 and LaCrO3/SrTiO3 heterointerfaces and uncover that the interfacial defects induce a significant change in electronic properties by showing an electronic transformation from the insulating state to metallic state at SrVO3/SrTiO3 heterointerfaces due to the hybridization of interfacial Ti d, O p and V d, and a metallic to insulating state transformation at LaCrO3/SrTiO3 because of Ti-Cr mixing induced charge redistribution in the interfacial layer.

  13. Crystallization study of SrTiO3 thin films prepared by dip coating

    Directory of Open Access Journals (Sweden)

    Edson R. Leite

    1999-04-01

    Full Text Available In this study, the crystallization process of SrTiO3 thin films, prepared by a chemical method, was characterized by Fourier Transformed Infra Red (FT-IR, Grazing Incident X-ray Diffraction (GIXRD, Thermal Analysis (TG and X-ray Absorption Near Edge Structure (XANES. The results showed that an amorphous inorganic phase is formed, consisting of clusters of oxygen five-coordinate titanium. The amorphous phase begins crystallizing at temperatures above 450 °C. No intermediate crystalline phase and no preferential orientation was observed for films deposited on MgO (100. FT-IR results suggest the presence of the carbonate group. However, the low thermal stability of this group and the low crystallization temperature of the observed SrTiO3 phase indicate that this carbonate is adsorbed.

  14. First-principles study of FeSe epitaxial films on SrTiO3

    Institute of Scientific and Technical Information of China (English)

    刘凯; 高淼; 卢仲毅; 向涛

    2015-01-01

    The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimen-tal and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasiz-ing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3 is discussed.

  15. Effects of Nb-doped on the structure and electrochemical performance of LiFePO4/C composites

    Science.gov (United States)

    Ma, Zhipeng; Shao, Guangjie; Wang, Guiling; Zhang, Ying; Du, Jianping

    2014-02-01

    The olivine-type niobium doping Li1-xNbxFePO4/C (x=0, 0.005, 0.010, 0.015, 0.025) cathode materials were synthesized via a two-step ball milling solid state reaction. The effects of Nb doping were charactered by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and galvanostatic charge-discharge. It is found that Nb doping enlarges the interplanar distance of crystal plane parallel to [0 1 0] direction in LiFePO4. In other words, it widens the one dimensional diffusion channels of Li+ along the [0 1 0] direction. Electrochemical test results indicate that the Li0.99Nb0.01FePO4/C composite exhibits the best electrochemical performance with initial special discharge capacity of 139.3 mA h g-1 at 1 C rate. The present synthesis route is promising in making the solid state reaction method more practical for preparation of the LiFePO4 material.

  16. Structural and spectroscopic properties of pure and doped Ba6Ti2Nb8O30 tungsten bronze.

    Science.gov (United States)

    Massarotti, V; Capsoni, D; Bini, M; Azzoni, C B; Mozzati, M C; Galinetto, P; Chiodelli, G

    2006-09-14

    Pure and doped Ba(6)Ti(2)Nb(8)O(30) (BTN), obtained by substituting M = Cr, Mn, or Fe on the Ti site (Ba(6)Ti(2-x) M(x)Nb(8)O(30), x = 0.06 and 0.18) and Y and Fe on the Ba and Ti sites, respectively (Ba(6-x)Y(x)Ti(2-x)Fe(x)Nb(8)O(30), x= 0.18), are synthesized. The influence of cation doping on the local structure, the cation oxidation state, and the possible defect formation able to maintain the charge neutrality are investigated by spectroscopic (electron paramagnetic resonance (EPR) and micro-Raman), structural (X-ray powder diffraction) and transport (impedance spectroscopy, thermoelectric power) measurements, in the temperature range of 300-1200 K in air and N(2) flow. Starting from the valence state of the doping ions (Fe(3+), Cr(3+), and Mn(2+)), determined by EPR, and from thermoelectric power measurements, evidencing a negative charge transport, different charge-compensating defect equilibria, based on the creation of positive electron holes or oxygen vacancies and electrons, are discussed to interpret the conductivity results.

  17. Room-temperature Ferroelectricity in Uniaxially Strained Single-crystalline SrTiO3 Freestanding Films

    Science.gov (United States)

    Lu, Di; Crossley, Sam; Yoon, Hyeok; Hikita, Yasuyuki; Hwang, Harold

    Single crystal pure bulk SrTiO3 (STO) is an incipient ferroelectric whose dielectric permittivity rises to high values as temperature is reduced, but remains paraelectric to the lowest observable temperatures. Ferroelectric phases of STO may be stabilized via doping and strain, whose common effect is to split the spatial free energy well of ionic displacements. With epitaxial strain of the order of a few percent, Curie temperatures TC ~293 K have been observed. By exploiting a highly novel process to exfoliate epitaxial oxide films deposited by pulsed laser deposition, we have isolated sub-100 nm-thick freestanding films of STO which are readily manipulated and mechanically strained to high levels. Measurements of the in-plane dielectric properties for various applied strains reveal a continuously tunable ferroelectric TC. A two-order-of-magnitude enhanced dielectric response is displayed by a 1.2%-strained sample at TC ~290 K, as compared with the same sample unstrained at the same temperature. This is consistent with a phenomenological Ginzburg-Landau model, and previous studies on anchored films. The functional properties of strained STO have generated intense interest and debate, and have been suggested for device applications due to e.g. high voltage-tunable dielectric properties. Our work exhibits strain as a continuously variable experimental degree of freedom, which can induce numerous functional effects.

  18. Reactive Coevaporation Synthesis and Characterization of SrTiO3 Thin Films

    Science.gov (United States)

    Yamaguchi, Hiromu; Matsubara, Shogo; Miyasaka, Yoichi

    1991-09-01

    SrTiO3 thin films were prepared by the reactive coevaporation method, where the Ti and Sr metals were evaporated in oxygen ambient with an E-gun and K-cell, respectively. A uniform depth profile in composition was achieved by altering the Ti evaporation rate according to the Sr evaporation rate change. A typical dielectric constant of 170 was measured on films of 75 nm in thickness. The in-situ annealing in oxygen plasma reduced the leakage current.

  19. Upper limit to magnetism in LaAlO3/SrTiO3 heterostructures

    Science.gov (United States)

    Fitzsimmons, Michael

    2012-02-01

    In 2004 Ohtomo and Hwang reported unusually high conductivity in LaAlO3 and SrTiO3 bilayer samples. Since then, metallic conduction, superconductivity, magnetism, and coexistence of superconductivity and ferromagnetism have been attributed to LaAlO3/SrTiO3 interfaces. Very recently, two studies have reported large magnetic moments attributed to interfaces from measurement techniques that are unable to distinguish between interfacial and bulk magnetism. Consequently, it is imperative to perform magnetic measurements that by being intrinsically sensitive to interface magnetism are impervious to experimental artifacts suffered by bulk measurements. Using polarized neutron reflectometry, we measured the neutron spin dependent reflectivity from four LaAlO3/SrTiO3 superlattices. Our results indicate the upper limit for the magnetization averaged over the lateral dimensions of the sample induced by an 11 T magnetic field at 1.7 K is less than 2 G. SQUID magnetometry of the neutron superlattice samples sporadically finds an enhanced moment (consistent with past reports), possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAlO3 and SrTiO3. Work performed in collaboration with N.W. Hengartner, S. Singh, M. Zhernenkov (LANL), F.Y. Bruno, J. Santamaria (Universidad Complutense de Madrid), A. Brinkman, M.J.A. Huijben, H. Molegraaf (MESA+ Institute for Nanotechnology), J. de la Venta and Ivan K. Schuller (UCSD). [4pt] Work supported by the Office of Basic Energy Science, U.S. Department of Energy, BES-DMS and DMR under grant DE FG03-87ER-45332. Work at UCM is supported by Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA) and work at Twente is supported by the Foundation for Fundamental Research on Matter (FOM).

  20. Structure of the photo-catalytically active surface of SrTiO3

    CERN Document Server

    Plaza, Manuel; Ko, J Y Peter; Brock, Joel D; Shen, Mei; Simpson, Burton H; Rodríguez-López, Joaquín; Ritzert, Nicole L; Abruña, Héctor D; Letchworth-Weaver, Kendra; Gunceler, Deniz; Arias, T A; Schlom, Darrell G

    2015-01-01

    A major goal of energy research is to use visible light to cleave water directly, without an applied voltage, into hydrogen and oxygen. Since the initial reports of the ultraviolet (UV) activity of TiO2 and SrTiO3 in the 1970s, researchers have pursued a fundamental understanding of the mechanistic and molecular-level phenomena involved in photo-catalysis. Although it requires UV light, after four decades SrTiO3 is still the gold standard for splitting water. It is chemically stable and catalyzes both the hydrogen and the oxygen reactions without applied bias. While ultrahigh vacuum (UHV) surface science techniques have provided useful insights, we still know relatively little about the structure of electrodes in contact with electrolytes under operating conditions. Here, we report the surface structure evolution of a SrTiO3 electrode during water splitting, before and after training with a positive bias. Operando high-energy X-ray reflectivity measurements demonstrate that training the electrode irreversibly...

  1. Nucleation kinetics of SrTiO3 3D islands and nanorings on Si substrates.

    Science.gov (United States)

    Tejedor, Paloma; Benedicto, Marcos; Vázquez, Luis; Galiana, Beatriz

    2014-11-07

    The nucleation of SrTiO3 three-dimensional (3D) islands and nanorings on Si substrates via a novel metalorganic decomposition (MOD) process has been investigated as a function of temperature and solution concentration of the SrTi(OC3H7)6 precursor. Quantitative analysis of island density and size distribution by atomic force microscopy (AFM) has revealed the existence of a nucleation regime at solution concentrations below 5 × 10(-3) M, in which the critical nucleus is a trimer and a coalescence regime at higher concentrations, dominated by growth of immobile clusters. Nanorings form preferentially under high supersaturation conditions and their size distribution is consistent with a dynamic coalescence. On the basis of recent theoretical models (Gill, 2012), we have proposed that the island-to-nanoring transition in the SrTiO3/Si system occurs above a critical size as a result of a competition between energetic and kinetic factors. The combination of high-resolution transmission electron microscopy (HRTEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) has shown that the monocrystalline SrTiO3 nanoclusters grow pseudomorphically on the Si substrate and exhibit a strain-induced tetragonal lattice distortion.

  2. 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.

  3. A promising electrode material modified by Nb-doped TiO2 nanotubes for electrochemical degradation of AR 73.

    Science.gov (United States)

    Xu, Li; Liang, Gaorui; Yin, Ming

    2017-04-01

    A distinctive SnO2Sb electrode with highly ordered Nb doped TiO2 nanotubes sheet as a new substrate, obtained by NbTi alloy anodization, is prepared by pulse electrochemical deposition for the first time as electrocatalytic oxidation anode for wastewater treatment. The novel electrode has a larger surface area and smaller crystallite particles than conventional SnO2Sb electrodes as obtained from the analysis of scanning electron microscopy and X-ray diffraction. Compared with Ti/SnO2Sb and Ti/TiO2-NTs/SnO2Sb prepared by pulse electrochemical deposition, the electrode modified by NbTiO2-NTs has the higher oxygen evolution potential of 2.29 V (vs. Ag/AgCl), and the lower charge transfer resistance, which decreased by 65% and 79%. The service lifetime of NbTi/NbTiO2-NTs/SnO2Sb is 4.9 times longer than that of Ti/SnO2Sb and 1.9 times longer than that of Ti/TiO2-NTs/SnO2Sb. The new electrode is proved to have an excellent electrochemical oxidation and degradation ability using Acid Red 73 as a target organic pollutant. The AR 73 removal, chemical oxygen demand removal and kinetic rate constant are increased obviously due to the introduction of NbTiO2-NTs. Besides, the energy consumption reduces 37.2% and 31.4% in contrast with Ti/SnO2Sb and Ti/TiO2-NTs/SnO2Sb. Hence, the Ti/SnO2Sb modified by NbTiO2-NTs is a very promising anode material for the electrochemical treatment of dye wastewater. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. 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).

  5. Structure and magnetic properties of spinel-perovskite nanocomposite thin films on SrTiO3 (111) substrates

    Science.gov (United States)

    Kim, Dong Hun; Yang, Junho; Kim, Min Seok; Kim, Tae Cheol

    2016-09-01

    Epitaxial CoFe2O4-BiFeO3 nanocomposite thin films were synthesized on perovskite structured SrTiO3 (001) and (111) substrates by combinatorial pulsed laser deposition and characterized using scanning electron microscopy, x-ray diffraction, and vibrating sample magnetometer. Triangular BiFeO3 nanopillars were formed in a CoFe2O4 matrix on (111) oriented SrTiO3 substrates, while CoFe2O4 nanopillars with rectangular or square top surfaces grew in a BiFeO3 matrix on (001) substrates. The magnetic hysteresis loops of nanocomposites on (111) oriented SrTiO3 substrates showed isotropic properties due to the strain relaxation while those of films on SrTiO3 (001) substrates exhibited a strong out-of-plane anisotropy originated from shape and strain effects.

  6. Top-seeded solution growth of SrTiO3 single crystals virtually free of mosaicity

    Science.gov (United States)

    Guguschev, Christo; Kok, Dirk J.; Juda, Uta; Uecker, Reinhard; Sintonen, Sakari; Galazka, Zbigniew; Bickermann, Matthias

    2017-06-01

    Strontium titanate (SrTiO3), a well-established traditional perovskite substrate as well as a promising substrate crystal for the epitaxy of new advanced perovskite-type thin films, suffers from the unavailability in adequate quality for the latter. To improve the situation attempts have been made to grow SrTiO3 at moderate temperatures (memory devices and to allow an in-depth analysis of intrinsic and extrinsic factors influencing the properties of epitaxially grown oxide heterostructures.

  7. Deposition of boron doped DLC films on TiNb and characterization of their mechanical properties and blood compatibility

    Science.gov (United States)

    Liza, Shahira; Hieda, Junko; Akasaka, Hiroki; Ohtake, Naoto; Tsutsumi, Yusuke; Nagai, Akiko; Hanawa, Takao

    2017-01-01

    Abstract Diamond-like carbon (DLC) material is used in blood contacting devices as the surface coating material because of the antithrombogenicity behavior which helps to inhibit platelet adhesion and activation. In this study, DLC films were doped with boron during pulsed plasma chemical vapor deposition (CVD) to improve the blood compatibility. The ratio of boron to carbon (B/C) was varied from 0 to 0.4 in the film by adjusting the flow rate of trimethylboron and acetylene. Tribological tests indicated that boron doping with a low B/C ratio of 0.03 is beneficial for reducing friction (μ = 0.1), lowering hardness and slightly increasing wear rate compared to undoped DLC films. The B/C ratio in the film of 0.03 and 0.4 exhibited highly hydrophilic surface owing to their high wettability and high surface energy. An in vitro platelet adhesion experiment was conducted to compare the blood compatibility of TiNb substrates before and after coating with undoped and boron doped DLC. Films with highly hydrophilic surface enhanced the blood compatibility of TiNb, and the best results were obtained for DLC with the B/C ratio of 0.03. Boron doped DLC films are promising surface coatings for blood contacting devices. PMID:28179961

  8. Morphology-Controlled Synthesis Of SrTiO3 Nanocube By Capping Agent-Assisted Solvothermal Method

    Directory of Open Access Journals (Sweden)

    Yulia Eka Putri

    2016-05-01

    Full Text Available The synthesis of SrTiO3 nanocubes have been carried out by solvothermal process using cetyl trimethyl ammonium bromide (CTAB as capping agent to control the particles morphology. The condition of the synthesis was obtained at 160 ºC for 24 hours with molar ratio of SrTiO3 and capping agent was 1 : 1. The X-ray diffraction (XRD pattern shows that SrTiO3 adopts a perovskite structure with a higher intensity of 110 at 2q:32.33º and the crystallite size calculated from FWHM was found to be 41 nm. Fourier transform infrared (FTIR spectrum shows a shift in particular absorption band attributed the interaction between SrTiO3 particles surface and the head group of CTAB molecules. Transmission electron microscopy (TEM image shows the cubic-like particles of SrTiO3, this indicatesthat CTAB successfully functions as capping agent on the synthesis of SrTiO3.

  9. An Understanding of the Photocatalytic Properties and Pollutant Degradation Mechanism of SrTiO3 Nanoparticles.

    Science.gov (United States)

    da Silva, Luís F; Lopes, Osmando F; de Mendonça, Vagner R; Carvalho, Kele T G; Longo, Elson; Ribeiro, Caue; Mastelaro, Valmor R

    2016-05-01

    Strontium titanate nanoparticles have attracted much attention due to their physical and chemical properties, especially as photocatalysts under ultraviolet irradiation. In this paper, we analyze the effect of heating rate during the crystallization process of SrTiO3 nanoparticles in the degradation of organic pollutants. The relationship between structural, morphological and photocatalytic properties of the SrTiO3 nanoparticles was investigated using different techniques. Transmission electron microscopy and N2 adsorption results show that particle size and surface properties are tuned by the heating rate of the SrTiO3 crystallization process. The SrTiO3 nanoparticles showed good photoactivity for the degradation of methylene blue, rhodamine B and methyl orange dyes, driven by a nonselective process. The SrTiO3 sample with the largest particle size exhibited higher photoactivity per unit area, independent of the molecule to be degraded. The results pointed out that the photodegradation of methylene blue dye catalyzed by SrTiO3 is caused by the action of valence band holes (direct pathway), and the indirect mechanism has a negligible effect, i.e. degradation by O2 (-•) and (•) OH radicals attack.

  10. Effects of A- and B-site (co-)acceptor doping on the structure and proton conductivity of LaNbO4

    DEFF Research Database (Denmark)

    Ivanova, M.; Ricote, Sandrine; Meulenberg, W.A.

    2012-01-01

    B-site and A- and B-site co-doped lanthanum niobates, La(1-x)DA(x)Nb(1-y)DB(y)O(4-δ), where DA stands for Ca or Ba and DB for Ga, Ge or In (x = 0 or 0.01; y = 0.01), have been synthesized via the solid-state route. Essentially single-phase materials were obtained after 10 h at 1500 °C with monocl...... of the B-site and A- and B-site co-doped LaNbO4 is slightly more exothermic and that the proton mobility has higher activation enthalpies than Ca-doped LaNbO4. This is accounted for by a stronger association between the acceptor and the proton for B-site than for A-site doping....

  11. Correlation between the band positions of (SrTiO3)1-x.(LaTiO2N)x solid solutions and photocatalytic properties under visible light irradiation.

    Science.gov (United States)

    Luo, Wenjun; Li, Zhaosheng; Jiang, Xiaojun; Yu, Tao; Liu, Lifei; Chen, Xinyi; Ye, Jinhua; Zou, Zhigang

    2008-11-28

    N-doped SrTiO3 and (SrTiO3)1-x.(LaTiO2N)x samples were prepared by the thermal ammonolysis method. The photocatalytic activities of the samples were investigated in a water suspension system. Aqueous methanol solution (50 mL CH3OH + 220 mL H2O) for H2 evolution and aqueous silver nitrate solution (270 mL, 0.01 mol L(-1)) for O2 evolution were used as sacrificial reagents. The oxynitrides showed photocatalytic activities under visible light irradiation. The maximum rates of photocatalytic hydrogen and oxygen evolution under visible light irradiation (lambda > 420 nm) were 10 and 8 micromol h(-1), respectively. The samples were characterized by X-ray diffractometry, UV-Vis spectrophotometry, Fourier transform infrared spectrometry, and laser Raman spectroscopy. The unit cell edge length of (SrTiO3)1-x.(LaTiO2N)x increased linearly and their band gaps reduced from 3.18 to 2.04 eV with increasing x from 0 to 0.30. Moreover, the calculation results of (SrTiO3)0.75.(LaTiO2N)0.25 by density functional theory suggested that the band gap narrowing of the solid solutions came from the hybridization of N2p and O2p orbital. The band positions of the solid solutions were further investigated by Mott-Schottky and the onset potential method. The results suggested that the conduction band of the solid solution was lowered, which led to decrement of the hydrogen evolution rate.

  12. Evidence of weak superconductivity at the room-temperature grown LaAlO3/SrTiO3 interface

    DEFF Research Database (Denmark)

    Prawiroatmodjo, G. E. D. K.; Trier, Felix; Christensen, Dennis Valbjørn;

    2016-01-01

    The two-dimensional electron gas at the crystalline LaAlO3/SrTiO3 (c-LAO/STO) interface has sparked large interest due to its exotic properties, including an intriguing gate-tunable superconducting phase. While there is growing evidence of pronounced spatial inhomogeneity in the conductivity at STO......-based interfaces, the consequences for superconductivity remain largely unknown. We study interfaces based on amorphous LAO top layers grown at room temperature (a-LAO/STO) and demonstrate a superconducting phase similar to c-LAO/STO, however, with a gate-tunable critical temperature of 460 mK. The dependence...... of the superconducting critical current on temperature, magnetic field, and back-gate-controlled doping is found to be consistently described by a model of a random array of Josephson-coupled superconducting domains....

  13. 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.

  14. 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}.

  15. 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.

  16. Crystal structure, electrical conductivity and thermal expansion of Ni and Nb co-doped LaCoO3.

    Science.gov (United States)

    Øygarden, Vegar; Grande, Tor

    2013-02-28

    The effect of co-doping LaCoO(3) with Ni and Nb has been investigated in the two solid solution series (1 - x)LaCoO(3)-xLaNi(2/3)Nb(1/3)O(3) and (1 - y)LaCo(2/3)Ni(1/3)O(3)-yLaNi(2/3)Nb(1/3)O(3). The materials were shown to be stoichiometric with respect to oxygen. The compositional effect on the evolution of the crystal structure, thermal expansion and electrical conductivity is reported. The chemical stability of LaCoO(3) in a reducing atmosphere was improved and the thermal expansion was suppressed at higher levels of Nb-substitution. The materials with mixed oxidation states on the B-site possessed superior electrical transport properties compared to solid solutions with cations in mainly isovalent oxidation states. The evolution of the electronic conductivity, thermal expansion and crystal structural is discussed with emphasis on the oxidation states of Ni and Co, and the spin transitions of Co.

  17. The Investigation of the Zr-doped LaNbO4 Thin Ceramic Films by Electrochemical Impedance Spectroscopy

    Directory of Open Access Journals (Sweden)

    Darius Virbukas

    2015-09-01

    Full Text Available Thin Zr-doped lanthanum niobium oxide (LaNb1-xZrxO4 films were formed on the optical quartz (SiO2 substrates using magnetron sputtering technique. Formed LaNb1-xZrxO4 thin films were characterized using different techniques: X-ray diffraction (XRD, scanning electron microscope (SEM and impedance spectroscopy. Electrical parameters of LaNb1-xZrxO4 thin ceramic were investigated in the frequency range from 0.1 Hz to 1.0 MHz in temperature range from 773 to 1173 K.It was determined that LaNb1-xZrxO4 thin ceramic films have the tetragonal structure and non-Debye type of relaxation. The activation energy was estimated from the relaxation time of impedance, electric modulus and conductivity resulting the activation energies vary from 1.12 ± 1 eV (Zr 1.99at.%, to 1.24 eV±1 eV (Zr 0.62at.%.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.9535

  18. The Investigation of the Zr-doped LaNbO4 Thin Ceramic Films by Electrochemical Impedance Spectroscopy

    Directory of Open Access Journals (Sweden)

    Darius Virbukas

    2015-09-01

    Full Text Available Thin Zr-doped lanthanum niobium oxide (LaNb1-xZrxO4 films were formed on the optical quartz (SiO2 substrates using magnetron sputtering technique. Formed LaNb1-xZrxO4 thin films were characterized using different techniques: X-ray diffraction (XRD, scanning electron microscope (SEM and impedance spectroscopy. Electrical parameters of LaNb1-xZrxO4 thin ceramic were investigated in the frequency range from 0.1 Hz to 1.0 MHz in temperature range from 773 to 1173 K.It was determined that LaNb1-xZrxO4 thin ceramic films have the tetragonal structure and non-Debye type of relaxation. The activation energy was estimated from the relaxation time of impedance, electric modulus and conductivity resulting the activation energies vary from 1.12 ± 1 eV (Zr 1.99at.%, to 1.24 eV±1 eV (Zr 0.62at.%.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.9535

  19. 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.)

  20. In Vitro Cytotoxicity of a Ti-35Nb-7Zr-5Ta Alloy Doped with Different Oxygen Contents

    Directory of Open Access Journals (Sweden)

    Tatiani Ayako Goto Donato

    2014-03-01

    Full Text Available Cp-Ti is the most common material used for dental implants, but its elastic modulus is around five times higher than that of bone. Recently, promising alloys that add Nb, Ta, Zr and Mo to Ti have been developed. The mechanical properties of these alloys are directly related to its microstructure and the presence of interstitial elements, such as oxygen, carbon, nitrogen and hydrogen. In this study, the in vitro cytotoxicity of Ti-35Nb-7Zr-5Ta (TNZT alloys was analyzed in the as-received condition and after being doped with several small quantities of oxygen on a cultured osteogenic cell. The cell’s morphology was also examined by scanning electron microscopy (SEM. The TNZT alloy presented no cytotoxic effects on osteoblastic cells in the studied conditions.

  1. Synthesis of SrTiO3 for immobilization of simulated HLW by SHS

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Strontium titanate synroc samples were synthesized by self-propagating high-temperature synthesis (SHS). Sr directly took part in the synthesis process. As a result, the loading content issue is basically resolved. The products were characterized by density, microhardness X-ray diffraction, and scanning electron microscopy (SEM/EDS). The leaching rate was measured by the method of PCT (product consistency test). The results indicate that the Sr2+-SrTiO3 compound is of high density, low leach rate and high stability and the synthesis process is feasible in technology and economy. It can be concluded that the strontium titanate synroc is a perfect material to immobilize HLW.

  2. Influence of the ferroelectric quantum critical point on SrTiO3 interfaces

    Science.gov (United States)

    Atkinson, W. A.; Lafleur, P.; Raslan, A.

    2017-02-01

    We study a model SrTiO3 interface in which conduction t2 g electrons couple to the ferroelectric (FE) phonon mode. We treat the FE mode within a self-consistent phonon theory that captures its quantum critical behavior and show that proximity to the quantum critical point leads to universal tails in the electron density of the form n (z ) ˜(λ+z ) -2 , where λ ˜T2 -d /z , with d =3 the dimensionality and z =1 the dynamical critical exponent. Implications for the metal-insulator transition at low electron density are discussed.

  3. Diversity of hydrogen configuration and its roles in SrTiO3−δ

    Directory of Open Access Journals (Sweden)

    Yoshiki Iwazaki

    2014-01-01

    Full Text Available As a source of carrier electron, various configurations of hydrogen in SrTiO3 are searched by using first-principles calculations. The most stable form of hydrogen is found to be H−, where doubly charged oxygen vacancy VO2+ changes into singly charged HO+. Most importantly, an additional H− is found to be weakly trapped by HO+, which completely neutralizes carrier electrons by forming (2HO0. These unexpected behaviors of hydrogen, which can explain reported experimental results, expand the role of the hydrogen in carrier-control technology in transition-metal oxides.

  4. Electric-field-induced soft-mode hardening in SrTiO3 films

    Science.gov (United States)

    Akimov; Sirenko; Clark; Hao; Xi

    2000-05-15

    We have studied electric-field-induced Raman scattering in SrTiO3 thin films using an indium-tin-oxide/SrTiO3/SrRuO3 structure grown by pulsed laser deposition. The soft mode polarized along the field becomes Raman active. Experimental data for electric-field-induced hardening of the soft modes and the tuning of the static dielectric constant are in agreement described by the Lyddane-Sachs-Teller formalism. The markedly different behavior of the soft modes in thin films from that in the bulk is explained by the existence of local polar regions.

  5. Phonon transport in perovskite SrTiO3 from first principles

    CERN Document Server

    Feng, Lei; Shiomi, Junichiro

    2015-01-01

    We investigate phonon transport in perovskite strontium titanate (SrTiO3) which is stable above its phase transition temperature (~105 K) by using first-principles molecular dynamics and anharmonic lattice dynamics. Unlike conventional ground-state-based perturbation methods that give imaginary phonon frequencies, the current calculation reproduces stable phonon dispersion relations observed in experiments. We find the contribution of optical phonons to overall lattice thermal conductivity is larger than 60%, markedly different from the usual picture with dominant contribution from acoustic phonons. The mode- and pseudopotential-dependence analysis suggests the strong attenuation of acoustic phonons transport originated from strong anharmonic coupling with the transversely-polarized ferroelectric modes.

  6. Electron spectroscopic investigation of metal-insulator transition in Ce1-SrTiO3

    Indian Academy of Sciences (India)

    U Manju; S R Krishnakumar; Sugata Ray; S Raj; M Onoda; C Carbone; D D Sarma

    2003-10-01

    We have carried out detailed electron spectroscopic investigation of Ce1-SrTiO3 exhibiting insulator-metal transition with . Core level X-ray photoelectron spectra of Ce 3 as well as resonant photoemission spectra obtained at the Ce 4 → 4 resonant absorption threshold establish Ce as being in the trivalent state throughout the series. Using the `off-resonance’ condition for Ce 4 states, we obtain the Ti 3 dominated spectral features close to , exhibiting clear signatures of coherent and incoherent peaks. We discuss the implications of our findings in relation to the metal-insulator transition observed in this series of compounds.

  7. The Spectral Properties of Zn doped LiNbO3 Crystals%掺锌LiNbO3晶体的光谱性质

    Institute of Scientific and Technical Information of China (English)

    赵业权; 徐悟生; 朱质彬; 张玥; 徐蔚青; 王继扬

    2000-01-01

    在LiNbO3中掺进2 mol%,4 mol%,6 mol%,8 mol%的ZnO,生长Zn(2 mol%):LiNbO3,Zn(4 mol%):LiNbO3,Zn(6 mol%):LiNbO3和Zn(8 mol%):LiNbO3晶体,测试LiNbO3和掺锌LiNbO3晶体的透射光谱.LiNbO3和掺锌LiNbO3晶体在350-900 nm的范围内都是透明的.Zn:LiNbO3晶体的吸收边发生紫移.对Zn:LiNbO3晶体吸收边紫移的机理进行探讨.

  8. Infrared and thermoelectric power generation in thin atomic layer deposited Nb-doped TiO{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Mann, Harkirat S.; Lang, Brian N.; Schwab, Yosyp; Scarel, Giovanna, E-mail: scarelgx@jmu.edu [Department of Physics and Astronomy, James Madison University, 901 Carrier Drive, Harrisonburg, Virginia 22807 (United States); Niemelä, Janne-Petteri; Karppinen, Maarit [Department of Chemistry, Aalto University, P.O. Box 16100, Aalto, 00076 Finland (Finland)

    2015-01-15

    Infrared radiation is used to radiatively transfer heat to a nanometric power generator (NPG) device with a thermoelectric Nb-doped TiO{sub 2} film deposited by atomic layer deposition (ALD) as the active element, onto a borosilicate glass substrate. The linear rise of the produced voltage with respect to the temperature difference between the “hot” and “cold” junctions, typical of the Seebeck effect, is missing. The discovery of the violation of the Seebeck effect in NPG devices combined with the ability of ALD to tune thermoelectric thin film properties could be exploited to increase the efficiency of these devices for energy harvesting purposes.

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

    KAUST Repository

    Yue, Chaochao

    2016-08-05

    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 content and mixtures of tungstite and niobic acid at higher Nb content. Tungstite is a promising catalyst for the dehydration of glucose to HMF. Compared with Nb2O5, fewer by-products are formed because of the low BrOnsted acidity of the (mixed) oxides. In water, an optimum yield of HMF was obtained for Nb-W oxides with low Nb content owing to balanced Lewis and BrOnsted acidity. In THF/water, the strong Lewis acidity and weak BrOnsted acidity caused the reaction to proceed through isomerization to fructose and dehydration of fructose to a partially dehydrated intermediate, which was identified by LC-ESI-MS. The addition of HCl to the reaction mixture resulted in rapid dehydration of this intermediate to HMF. The HMF yield obtained in this way was approximately 56% for all tungstite catalysts. Density functional theory calculations show that the Lewis acid centers on the tungstite surface can isomerize glucose into fructose. Substitution of W by Nb lowers the overall activation barrier for glucose isomerization by stabilizing the deprotonated glucose adsorbate.

  10. 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)

  11. 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.

  12. Synthesis, structural characterization and dielectric properties of Nb doped BaTiO{sub 3}/SiO{sub 2} core–shell heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Cernea, M., E-mail: mcernea@infim.ro [National Institute of Materials Physics, P.O. Box MG-7, Bucharest-Magurele 077125 (Romania); Vasile, B.S. [University POLITEHNICA of Bucharest, Bucharest 060042 (Romania); Boni, A.; Iuga, A. [National Institute of Materials Physics, P.O. Box MG-7, Bucharest-Magurele 077125 (Romania)

    2014-02-25

    Highlights: • Optimal parameters for preparation by sol–gel of core–shell (BT-Nb{sub 0.005})/SiO{sub 2} are presented in this paper. • Single crystalline BT-Nb{sub 0.005}/SiO{sub 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{sub 3} doped with 0.5 mol%Nb{sub 2}O{sub 5} and then nanocoated with SiO{sub 2} (abbreviated as BT-Nb{sub 0.005}/SiO{sub 2}) was successful prepared using conventional sol–gel processing. Phase composition, particle morphology, structure, and electric properties of BT-Nb{sub 0.005} core and BT-Nb{sub 0.005}/SiO{sub 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{sub 3} was achieved. Furthermore, single crystalline BT-Nb{sub 0.005}/SiO{sub 2} core–nanoshell heterostructure with ∼34 nm shell thick was prepared, which is a novelty in ferroelectrics field. The ferroelectric quality of BT-Nb{sub 0.005} has suffered an alteration when the (BT-Nb{sub 0.005})/SiO{sub 2} core–shell heterostructure was realized. One-dimensional BT-Nb{sub 0.005}/SiO{sub 2} core–shell heterostructure exhibits an improvement of dielectric losses and a decrease of dielectric constant, compared to uncoated BT-Nb{sub 0.005}. The (BT-Nb{sub 0.005})/SiO{sub 2} core–shell material could be interesting for application in the composite capacitors.

  13. Large piezoelectricity in electric-field modified single crystals of SrTiO3

    Science.gov (United States)

    Khanbabaee, B.; Mehner, E.; Richter, C.; Hanzig, J.; Zschornak, M.; Pietsch, U.; Stöcker, H.; Leisegang, T.; Meyer, D. C.; Gorfman, S.

    2016-11-01

    Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3, this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.

  14. Nature of weak magnetism in SrTiO3/LaAlO3 multilayers.

    Science.gov (United States)

    Salman, Z; Ofer, O; Radovic, M; Hao, H; Ben Shalom, M; Chow, K H; Dagan, Y; Hossain, M D; Levy, C D P; Macfarlane, W A; Morris, G M; Patthey, L; Pearson, M R; Saadaoui, H; Schmitt, T; Wang, D; Kiefl, R F

    2012-12-21

    We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.

  15. Temperature-dependent band structure of SrTiO3 interfaces

    Science.gov (United States)

    Raslan, Amany; Lafleur, Patrick; Atkinson, W. A.

    2017-02-01

    We build a theoretical model for the electronic properties of the two-dimensional (2D) electron gas that forms at the interface between insulating SrTiO3 and a number of polar cap layers, including LaTiO3, LaAlO3, and GdTiO3. The model treats conduction electrons within a tight-binding approximation and the dielectric polarization via a Landau-Devonshire free energy that incorporates strontium titanate's strongly nonlinear, nonlocal, and temperature-dependent dielectric response. The self-consistent band structure comprises a mix of quantum 2D states that are tightly bound to the interface and quasi-three-dimensional (3D) states that extend hundreds of unit cells into the SrTiO3 substrate. We find that there is a substantial shift of electrons away from the interface into the 3D tails as temperature is lowered from 300 K to 10 K. This shift is least important at high electron densities (˜1014cm-2 ) but becomes substantial at low densities; for example, the total electron density within 4 nm of the interface changes by a factor of two for 2D electron densities ˜1013cm-2 . We speculate that the quasi-3D tails form the low-density high-mobility component of the interfacial electron gas that is widely inferred from magnetoresistance measurements.

  16. Structural and Magnetic Properties of LaCoO3/SrTiO3 Multilayers.

    Science.gov (United States)

    Zhang, Hongrui; Zhang, Jing; Yang, Huaiwen; Lan, Qianqian; Hong, Deshun; Wang, Shufang; Shen, Xi; Khan, Tahira; Yu, Richeng; Sun, Jirong; Shen, Baogen

    2016-07-20

    Structural and magnetic properties of the LaCoO3/SrTiO3 (LCO/STO) multilayers (MLs) with a fixed STO layer of 4 nm but varied LCO layer thicknesses have been systematically studied. The MLs grown on Sr0.7La0.3Al0.65Ta0.35O3 (LSAT) and SrTiO3 (STO) exhibit the in-plane lattice constant of the substrates, but those on LaAlO3 (LAO) show the in-plane lattice constant between those of the first two kinds of MLs. Compared with the LCO single layer (SL), the magnetic order of the MLs is significantly enhanced, as demonstrated by a very slow decrease, which is fast for the SL, of the Curie temperature and the saturation magnetization as the LCO layer thickness decreases. For example, clear ferromagnetic order is observed in the ML with the LCO layer of ∼1.5 nm, whereas it vanishes below ∼6 nm for the LCO SL. This result is consistent with the observation that the dark stripes, which are believed to be closely related to the magnetic order, remain clear in the MLs while they are vague in the corresponding LCO SL. The present work suggests a novel route to tune the magnetism of perovskite oxide films.

  17. Properties of epitaxial LaMnO3/SrTiO3 interfaces.

    Science.gov (United States)

    Christen, Hans M.; Kim, Dae Ho; Lee, Ho Nyung; Varela, Maria; Petit, Leon; Schulthess, Thomas

    2007-03-01

    Electronic effects at interfaces between dissimilar oxides are known to have fundamental consequences on their transport and magnetic properties. Interfaces between the band insulator SrTiO3 and the antiferromagnetic charge-transfer insulator LaMnO3 provide a particularly interesting platform to test such effects. Both perovskites are grown epitaxially by pulsed-laser deposition, and electron energy loss spectra (EELS) collected in a scanning transmission electron microscope (STEM) show interfacial valence changes on the Mn-sites, while Ti remains in a 4+ state even in direct contact with the LaO layer of the LaMnO3. This observation is fully consistent with computational results obtained for such structures using the self-interaction corrected (SIC) local spin density (LSD) method. In this presentation, we discuss the physical origin and consequences of these valence changes in single interfaces as well as LaMnO3/SrTiO3 superlattices. This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory (ORNL), managed and operated by UT-Battelle, LLC, and ORNL's Laboratory Directed Research and Development Program.

  18. Piezoelectric Properties of CuO-Doped (K,Na)NbO3 Lead-Free Ceramics Synthesized with Hydrothermal Powders

    Science.gov (United States)

    Yokouchi, Yuriko; Maeda, Takafumi; Bornmann, Peter; Hemsel, Tobias; Morita, Takeshi

    2013-07-01

    We report the piezoelectric properties of CuO-doped hydrothermal (K,Na)NbO3 ceramics that can be applied as hard-type lead-free piezoelectric ceramics. To date, we have succeeded in synthesizing high-quality KNbO3 and NaNbO3 powders by the hydrothermal method, which is based on an ionic reaction at high temperature (around 210 °C) and pressure. Increasing both the piezoelectric constant d and the mechanical quality factor (Qm) is important for resonance-type piezoelectric devices, such as ultrasonic motors and transformers. CuO doping into hydrothermal (K,Na)NbO3 ceramics was examined to realize hard-type lead-free piezoelectric ceramics. By doping with 1.2 mol % CuO, Qm was increased and the dielectric loss (tan δ) was decreased to 0.5%. The grain size was also influenced by the amount of CuO doping, which indicates that Qm is related to the density. To achieve a higher Qm value, the grain size is required to be less than 5 µm however, excessive CuO doping leads to anomalous grain growth. Optimal piezoelectric properties were obtained for 1.2 mol % CuO-doped (K,Na)NbO3; k31 = 0.32, d31 = -44 pC/N, Qm (radial) = 959, and tan δ= 0.5%. These characteristics showed that CuO doping with hydrothermal powders is effective for obtaining hard-type ceramics, and the mechanical quality factor is more than ten times higher than that of nondoped hydrothermal (K,Na)NbO3 ceramics. Therefore, compared with the conventional solid-state method, we could succeed in obtaining hard-type ceramics by a simple and short process.

  19. 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.

  20. Electro-mechanical response of top-gated LaAlO3/SrTiO3

    Science.gov (United States)

    Bi, Feng; Huang, Mengchen; Bark, Chung-Wung; Ryu, Sangwoo; Lee, Sanghan; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2016-01-01

    LaAlO3/SrTiO3 heterostructures are known to exhibit a sharp, hysteretic metal-insulator transition (MIT) with large enhanced capacitance near depletion. To understand the physical origin of this behavior, the electromechanical response of top-gated LaAlO3/SrTiO3 heterostructures is probed using two simultaneous measurement techniques: piezoresponse force microscopy (PFM) and capacitance spectroscopy. The observed hysteretic PFM responses show strong correlation with the capacitance signals, suggesting an interfacial carrier-mediated structural distortion associated with the gate-tuned MIT. In addition, the frequency dependence of the capacitance enhancement in LaAlO3/SrTiO3 is found to be well-matched to local PFM measurements. Our experimental results provide a fuller understanding of the top-gate tuned MIT in oxide heterostructure, which could be helpful for the development of future oxide-based nanoelectronics.

  1. Bioactive SrTiO(3) nanotube arrays: strontium delivery platform on Ti-based osteoporotic bone implants.

    Science.gov (United States)

    Xin, Yunchang; Jiang, Jiang; Huo, Kaifu; Hu, Tao; Chu, Paul K

    2009-10-27

    Development of strontium releasing implants capable of stimulating bone formation and inhibiting bone resorption is a desirable solution for curing osteoporosis. In this work, well-ordered SrTiO(3) nanotube arrays capable of Sr release at a slow rate and for a long time are successfully fabricated on titanium by simple hydrothermal treatment of anodized titania nanotubes. This surface architecture combines the functions of nanoscaled topography and Sr release to enhance osseointegration while at the same time leaving space for loading of other functional substances. In vitro experiments reveal that the SrTiO(3) nanotube arrays possess good biocompatibility and can induce precipitation of hydroxyapatite from simulated body fluids (SBF). This Ti-based implant with SrTiO(3) nanotube arrays is an ideal candidate for osteoporotic bone implants. The proposed method can also be extended to load other biologically useful elements such as Mg and Zn.

  2. Morphology, Orientation Relationship and Stability Analysis of Cu2O nanoclusters on SrTiO3 (100)

    Energy Technology Data Exchange (ETDEWEB)

    Kuchibhatla, Satyanarayana V N T; Hu, Shenyang Y.; Yu, Zhongqing; Shutthanandan, V.; Li, Ye; Nachimuthu, Ponnusamy; Jiang, Weilin; Thevuthasan, Suntharampillai; Henager, Charles H.; Sundaram, S. K.

    2009-08-03

    Reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM) and theoretical studies based on classical nucleation theory have been used to understand the morphology, orientation relationship and stability of Cu2O nanoclusters on SrTiO3 (100) (STO). We propose that the competing interfacial and elastic energies facilitate an in-plane rotation of the Cu2O clusters by 45o with respect to the STO substrate and stabilize Cu2O clusters on STO(100) with an orientation relationship of (001) Cu 2o //(001) SrTiO3 and <100> Cu 2o //<110> SrTiO3. Preliminary theoretical analysis also suggests that this particular orientation results in smaller critical nucleus sizes and lower nucleation barriers. The study also indicates a chemical potential (growth rate) dependence of the orientation relationship.

  3. Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

    Science.gov (United States)

    McDaniel, Martin D.; Posadas, Agham; Ngo, Thong Q.; Karako, Christine M.; Bruley, John; Frank, Martin M.; Narayanan, Vijay; Demkov, Alexander A.; Ekerdt, John G.

    2014-06-01

    Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5-25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1-xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (˜225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ˜2.0 × 10-2 Ω cm for 20-nm-thick La:STO (x ˜ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.

  4. Synthesis and characterization of -Bi2O3 based solid electrolyte doped with Nb2O5

    Indian Academy of Sciences (India)

    Handan Ozlu; Soner Cakar; Caner Bilir; Ersay Ersoy; Orhan Turkoglu

    2014-06-01

    -phase bismuth oxide is a well known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). This study aims to determine new phases of Bi2O3–Nb2O5 binary system and the temperature dependence of the electrical transport properties. The reaction products obtained in open air atmosphere were characterized by X-ray powder diffractions (XRD). The unit cell parameters were defined from the indexes of the powder diffraction patterns. The -Bi2O3 crystal system were obtained by doping 0.01 < mole% Nb2O5 < 0.04 at 750 °C for 48 and 96 h. Thermal behaviour and thermal stability of the phases were investigated by thermal analysis techniques. Surface and grain properties of the related phases were determined by SEM analysis. The temperature dependence of the electrical properties of -Bi2O3 solid solution was measured by four-point probe d.c. conductivity method. In the investigated system, the highest value of conductivity was observed for $\\sigma_{T}$ = 0.016 ohm-1 cm-1 at 650 °C on 4 mole% Nb2O5 addition. The electrical conductivity curves of studied materials revealed regular increase with temperature in the form of the Arrhenius type conductivity behaviour.

  5. Structural and impedance analysis of Co-doped SrTiO3 perovskite

    Science.gov (United States)

    Echeverri, E.; Arnache, O.

    2016-02-01

    SrTi1-xCoxO3 (0.2≥x≥0) polycrystalline samples were prepared by solid-state reaction. X-ray diffraction (XRD) analysis shown the perovskite type structure is conserved for all samples without impurities. A small increase in the lattice parameters were observed for x≥0.05. Morphology and composition were analysed by scanning electron microscopy (SEM- EDX). Impedance spectroscopy measurements form 50Hz to 1MHz were made at different temperatures (25-400°C). The spectra were analysed by Z' vs Z'' plots, which reveal 3 contributions associated to electrodes, grain boundary and grain. From the fits the frequency f) and times relaxation (τ) of the grain were estimated, with values of f∼15KHz and τ∼67µs for 20% Co samples at RT. A dispersion in the permittivity ε* at low frequency (<300Hz) were observed, which increase with the temperature. Each component of ε* converge for frequencies up to ∼300kHz. Finally, a behaviour and activation energy analysis of the electrical conductivity is presented from ln(σ) vs 1/T plots.

  6. Low temperature dielectric and magnetic properties of Fe-ion-doped SrTiO3

    Science.gov (United States)

    Fujishita, Hideshi; Arai, Yuya; Okamoto, Hiroyuki; Yamaguchi, Toshihisa

    2017-09-01

    Dielectric and magnetic properties of SrTi1-xFexO3 were measured for a single crystal sample (x=0.0032) and a ceramic sample (x=0.02). Temperature dependences of the dielectric constants were analyzed on the basis of a Vendik's formula, which describes a quantum paraelectric state accurately. A small amount of Fe impurities in the single crystal does not affect the characteristic temperatures of the dielectric properties, but does affect the quality of the crystal. This change in quality causes a large change in the dielectric constant of the quantum paraelectric state. The temperature dependence of the dielectric constant of the quantum paraelectric state of the ceramic sample is different from that of the single crystal not only quantitatively, but also qualitatively. The magnetic susceptibilities obey the typical Curie law, though a deviation of the Curie law was observed below 5 K for x=0.02. Crystals with the both concentrations remain in paramagnetic states at 2.5 K. The magnetic properties of SrTi1-xFexO3 can, in all likelihood, be explained by the orientation effect of free Fe3+ ions. In addition, an antiferroelectric interaction suggested for EuTiO3 by an analysis of dielectric constants based on a Barrett's formula was turned out to be unnecessary following analysis of the same data based on the Vendik's formula.

  7. Near-stoichiometric Ti-diffused LiNbO(3) strip waveguide doped with Zr(4+).

    Science.gov (United States)

    Zhang, De-Long; Yang, Xiao-Fei; Zhang, Qun; Wong, Wing-Han; Yu, Dao-Yin; Pun, Edwin Yue-Bun

    2015-11-15

    We report a near-stoichiometric Ti:Zr:LiNbO(3) strip waveguide fabricated from a congruent substrate with a technological process in the following sequence: Zr4+-diffusion-doping, diffusion of 8-μm-wide, 100-nm-thick Ti strips, and post-Li-rich vapor transport equilibration. We show that Zr(4+)-doping has little effect on the LiNbO(3) refractive index, and the waveguide is in a near-stoichiometric environment. The waveguide well supports both the TE and TM modes, shows weak polarization dependence, is in single mode at the 1.5 μm wavelength, and has a loss of ≤0.6/0.8 dB/cm for the TE/TM modes. A secondary ion mass spectrometry analysis shows that the Zr(4+)-profile part with a concentration above the threshold of photorefractive damage entirely covers the waveguide, implying that the waveguide would be optical-damage resistant.

  8. Room temperature nonlinear magnetoelectric effect in lead-free and Nb-doped AlFeO{sub 3} compositions

    Energy Technology Data Exchange (ETDEWEB)

    Cótica, Luiz F., E-mail: lfcotica@dfi.uem.br [Department of Electrical and Computer Engineering, University of Texas at San Antonio, San Antonio, Texas 78249 (United States); Department of Physics, State University of Maringá, Maringá – PR 87020-900 (Brazil); Santos, Guilherme M.; Santos, Ivair A. [Department of Physics, State University of Maringá, Maringá – PR 87020-900 (Brazil); Freitas, Valdirlei F. [Department of Physics, Universidade Estadual do Centro-Oeste, Guarapuava – PR 85040-080 (Brazil); Coelho, Adelino A. [Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, Campinas – SP 13083-859 (Brazil); Pal, Madhuparna; Guo, Ruyan; Bhalla, Amar S. [Department of Electrical and Computer Engineering, University of Texas at San Antonio, San Antonio, Texas 78249 (United States); Garcia, Ducinei; Eiras, José A. [Department of Physics, Federal University of São Carlos, São Carlos – SP 13565-905 (Brazil)

    2015-02-14

    It is still a challenging problem to obtain technologically useful materials displaying strong magnetoelectric coupling at room temperature. In the search for new effects and materials to achieve this kind of coupling, a nonlinear magnetoelectric effect was proposed in the magnetically disordered relaxor ferroelectric materials. In this context, the aluminum iron oxide (AlFeO{sub 3}), a room temperature ferroelectric relaxor and magnetic spin glass compound, emerges as an attractive lead-free magnetoelectric material along with nonlinear magnetoelectric effects. In this work, static, dynamic, and temperature dependent ferroic and magnetoelectric properties in lead-free AlFeO{sub 3} and 2 at. % Nb-doped AlFeO{sub 3} multiferroic magnetoelectric compositions are studied. Pyroelectric and magnetic measurements show changes in ferroelectric and magnetic states close to each other (∼200 K). The magnetoelectric coefficient behavior as a function of H{sub bias} suggests a room temperature nonlinear magnetoelectric coupling in both single-phase and Nb-doped AlFeO{sub 3}-based ceramic compositions.

  9. Host-Sensitized NIR Quantum Cutting Emission in Nd(3+) Doped GdNbO4 Phosphors and Effect of Bi(3+) Ion Codoping.

    Science.gov (United States)

    Shahi, Praveen Kumar; Singh, Priyam; Rai, Shyam Bahadur; Bahadur, Amresh

    2016-02-15

    Host-sensitized near-infrared quantum cutting (QC) emission has been demonstrated in Nd(3+) doped Gd(1-x)Nd(x)NbO4 phosphors for various x values. Further, the effect of Bi(3+) ion addition as a sensitizer on near-infrared QC is studied in detail. X-ray diffraction confirms a monoclinic structure for pure and Nd(3+) doped phosphors. Pulsed laser excitation at 266 nm of Gd(1-x)Nd(x)NbO4 and Gd(0.99-x)Nd(x)Bi(0.01)NbO4 causes efficient room-temperature energy transfer from the NbO4(3-) to the Nd(3+) ions and the NbO4(3-) and Bi(3+) ions to the Nd(3+) ions, respectively, which emits more than one near-infrared photon for single impinging ultraviolet photon. The emission band of Nd(3+) shows unusual character where the intensity of the (4)F(3/2)-(4)I(9/2) transition at 888 nm is higher than the intensity of the transition (4)F(3/2)-(4)I(11/2) at 1064 nm, due to energy transfer from GdNbO4 host to Nd(3+) ion. Using photoluminescence lifetime studies, the quantum cutting efficiencies are found to be the maximum 166% and 172% for Gd(0.95)Nd(0.05)NbO4 and Gd(0.94)Nd(0.05)Bi(0.01)NbO4, respectively. The present study could establish Nd(3+) ion as an alternative of Yb(3+) ion for near-infrared quantum cutting. This work facilitates the probing of Nd(3+) ions doped phosphor materials for next generation Si-solar cells.

  10. Spin-Orbit-Enhanced Functionality in LaAlO3/SrTiO3 Nanostructures

    Science.gov (United States)

    2015-09-16

    two- dimensional electron gas and conductivity switching of nanowires at the LaAlO3/SrTiO3 interface grown by 90° off-axis sputtering," Applied...rectangular area that is 200 nm wide. Transport experiments are performed as a function of a plane-perpendicular magnetic field up to 50 kOe, and as a... insulator transition of the LaAlO3/SrTiO3 interface with a conductive-atomic force microscope (c-AFM) technique has enabled a variety of electrical and

  11. The effect of Nd and Mg doping on the micro-Raman spectra of LiNbO{sub 3} single-crystals

    Energy Technology Data Exchange (ETDEWEB)

    Quispe-Siccha, R; Villagran-Muniz, M [Laboratorio de FotofIsica, Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, AP 70-186, DF (Mexico); MejIa-Uriarte, E V [Laboratorio de Fotonica de Microondas, Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, AP 70-186, DF (Mexico); Jaque, D; GarcIa Sole, J; Jaque, F [Laboratorio de Espectroscopia Laser, Departamentode Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Sato-Berru, R Y [Laboratorio de Materiales y NanotecnologIa, Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, AP 70-186, DF (Mexico); Camarillo, E; Hernandez A, J; Murrieta S, H [Laboratorio Propiedades Opticas, Instituto de Fisica, Universidad Nacional Autonoma de Mexico, AP 20-364 (Mexico)], E-mail: rosa.quispe@gmail.com, E-mail: elsi.mejia@ccadet.unam.mx, E-mail: mayo.villagran@ccadet.unam.mx, E-mail: dani.jaque@uam.es, E-mail: jose.garcia_sole@uam.es, E-mail: francisco.jaque@uam.es, E-mail: roberto.sato@ccadet.unam.mx, E-mail: cgarcia@fisica.unam.mx, E-mail: josemh@fisica.unam.mx, E-mail: murrieta@fisica.unam.mx

    2009-04-08

    The LiNbO{sub 3} congruent crystals doped with small Nd concentrations, <1 mol% Nd, and co-doped with Mg ions, 0-9 mol% Mg, were systematically investigated by means of micro-Raman spectroscopy in the Y and Z crystal directions. Results obtained from an undoped congruent crystal, an Nd-doped crystal, a Mg-doped crystal and Nd, Mg-co-doped crystals are compared. From the analyses of the results obtained in the Y direction, the Nd and Mg content dependence of the two lowest-Raman A{sub 1}(TO{sub 1}) and A{sub 1}(TO{sub 2}) modes, the half-width composition and the area ratio of the A{sub 1}(TO{sub 4}) and E(TO{sub 8}) bands, we reached several conclusions about the incorporation mechanism of the Nd and Mg ions into the LiNbO{sub 3} lattice. Likewise the Raman shift and half-width of the E(TO{sub 1}) and E(TO{sub 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.

  12. 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.

  13. Influence of Nb5+ Doping on Structure and Electrochemical Properties of Spinel Li1.02Mn2O4%Influence of Nb5+ Doping on Structure and Electrochemical Properties of Spinel Li1.02Mn2O4

    Institute of Scientific and Technical Information of China (English)

    Jianzhong Li; Yanwen Tian; Chaqing Xu

    2012-01-01

    The Li1.02NbxMn2-xO4 (x=0, 0.005, 0.01, 0.0:2, 0.04 and 0.1) materials were prepared by solid-state reaction method in which Li2CO3, electrolytic MnO2 and Nb2O5 were used as reactants. The influences of the Nb5+ doping on structure, morphology and electrochemical performance were systemically investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and AC impedance. XRD test showed that the prepared samples had single spinel structure although there was impurity phase of LiNbO3 existing in Li1.02NbxMn2-xO4 phase after Nb5+ doping. The doped materials with Nb5+ had smaller lattice parameters and crystal volume compared with pristine Li1.02Mn2O4. The endurance of overcharge was largely improved. In addition, the small amount of Nb5+ doping could increase the material conductivity.

  14. Martensitic transformation and magnetocaloric effect in Mn-Ni-Nb-Sn shape memory alloys: The effect of 4d transition-metal doping

    Energy Technology Data Exchange (ETDEWEB)

    Han Zhida, E-mail: zhida.han@gmail.com [Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Jiangsu Laboratory of Advanced Functional Materials, Changshu Institute of Technology, Changshu 215500 (China); Department of Physics, Nanjing University, Nanjing 210093 (China); Chen Xi; Zhang Yao; Chen Jie [Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Qian Bin; Jiang Xuefan [Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Jiangsu Laboratory of Advanced Functional Materials, Changshu Institute of Technology, Changshu 215500 (China); Wang Dunhui; Du Youwei [Department of Physics, Nanjing University, Nanjing 210093 (China)

    2012-02-25

    Highlights: Black-Right-Pointing-Pointer The first study of 4d transition-metal addition in Ni-Mn-based ferromagnetic shape memory alloys. Black-Right-Pointing-Pointer The martensitic transformation temperatures decrease with the increase of Nb content. Black-Right-Pointing-Pointer 4d transition-metal doping provide an alternative way to tailor the phase transitions and magnetocaloric effect Ni-Mn-X (X = In, Sn, Sb) alloys. - Abstract: The influence of 4d transition-metal Nb substitution for Ni in Mn{sub 50}Ni{sub 50-y}Sn{sub y} (y = 9, 10) alloys on the phase transitions and magnetocaloric effect was investigated. Austenitic phase of Nb-doped Mn{sub 50}Ni{sub 50-y}Sn{sub y} alloys have the cubic structure, and Nb addition results in the expansion of cell volume. The martensitic transformation temperatures decrease with the increase of Nb content, which could be explained by the decrease of valence electron concentration. Our results indicate that 4d transition-metal doping may provide an alternative way to tailor the martensitic transformation and the magnetocaloric effect in ferromagnetic shape memory alloys.

  15. Ab initio studies of Nb-N-S tri-doped TiO2 with enhanced visible light photocatalytic activity

    Science.gov (United States)

    Ren, Dahua; Cheng, Junxia; Cheng, Xinlu

    2016-06-01

    The electronic and optical properties of Nb-N-S tri-doped anatase TiO2 were investigated within the frame of the density functional theory (DFT) plus U method. Results show that a significant red-shift effect and improvement of visible-light absorption for Nb-N-S tri-doped TiO2 are observed with respect to pure TiO2 and S-N codoped TiO2. At the same time, the enhanced visible-light photocatalytic activity of tri-doped TiO2 is derived from the narrowing band gap, the appearance of Nb 4d state at the bottom of conduction band and the mixture of N 2p, S 3p states forming new defect levels at the top of valance band, which is excellently consistent with the previous experiment. Moreover, S ion leads to the lattice distortion and promotes the visible-light photocatalytic activity. Furthermore, the absorbance of 1.39NbNS-TiO2 accords well with the experimental result in the visible region. It is also found that the 2.78NbNS-TiO2 can be easily grown under O-rich condition and have the strongest absorbance from 2.0 to 4.2 eV among four models.

  16. Energy Spectra, g Factors and Their Pressure-Induced and/or Thermal Shifts of SrTiO3:Cr3+ and SrTiO3:Mn4+ I: Energy Spectra and g Factors at Normal Pressure

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ji-Ping; MA Dong-Ping

    2001-01-01

    With the strong-field scheme and cubic bases, the complete d3 energy matrix in a tctragonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectra of Sr TiO3 :Cr3+ and Sr TiO3 :Mn4+ at normal pressure and various temperatures have been calculated. Correspondingly, the FORTRAN program calculating the g factor of the ground state has been worked out. By using the program and the wavefunction obtained from diagonalizing the complete energy matrix, the g factors of the ground state of SrTiO3 :Cr3+ and SrTiO3 :Mn4+ at normal pressure and room temperature have been evaluated. The calculated results are in good agreement with the optical spectral and EPR experimental data. The comparison and analysis of the results of two crystals have been made. It is demonstrated that the covalency of the bonding between Mn4+ and ligands (O2 ) in SrTiO3:Mn4+ is stronger than the one of the bonding between Cr3+ and ligands (O2 ) in SrTiO3:Cr3+. It is shown that the obtained wavefunctions and values of parameters are reasonable.

  17. Increased fluorescence intensity in CaTiO3:Pr3+ phosphor due to NH3 treatment and Nb Co-doping

    Science.gov (United States)

    Holliday, K. S.; Kohlgruber, T. A.; Tran, I. C.; Åberg, D.; Seeley, Z. M.; Bagge-Hansen, M.; Srivastava, A. M.; Cherepy, N. J.; Payne, S. A.

    2016-10-01

    Development of next generation red phosphors for commercial lighting requires understanding of how increased luminescence is achieved by various treatment strategies. In this work, we compare co-doping with Nb to NH3 treatment of CaTiO3:Pr phosphors to reveal a general mechanism responsible for the increased luminescence. The phosphors were synthesized using standard solid-state synthesis techniques and the fluorescence was characterized for potential use in fluorescent lighting, with 254 nm excitation. The lifetime of the fluorescence was determined and used to identify a change in a trap state by the co-doping of Nb5+ in the phosphor. The oxidation state of the Pr was probed by NEXAFS and revealed that both Nb5+ co-doping and NH3 treatment reduced the number of non-fluorescing Pr4+ centers. Calculations were performed to determine the energetically favorable defects. Vacuum annealing was also used to further probe the nature of the trap state. It was determined that NH3 treatments reduce the number of Pr4+ non-fluorescing centers, while Nb5+ co-doping additionally reduces the number of excess oxygen trap states that quench the fluorescence.

  18. Improved electron transfer and plasmonic effect in dye-sensitized solar cells with bi-functional Nb-doped TiO2/Ag ternary nanostructures.

    Science.gov (United States)

    Park, Jung Tae; Chi, Won Seok; Jeon, Harim; Kim, Jong Hak

    2014-03-07

    TiO2 nanoparticles are surface-modified via atom transfer radical polymerization (ATRP) with a hydrophilic poly(oxyethylene)methacrylate (POEM), which can coordinate to the Ag precursor, i.e. silver trifluoromethanesulfonate (AgCF3SO3). Following the reduction of Ag ions, a Nb2O5 doping process and calcination at 450 °C, bi-functional Nb-doped TiO2/Ag ternary nanostructures are generated. The resulting nanostructures are characterized by energy-filtering transmission electron microscopy (EF-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. The dye-sensitized solar cell (DSSC) based on the Nb-doped TiO2/Ag nanostructure photoanode with a polymerized ionic liquid (PIL) as the solid polymer electrolyte shows an overall energy conversion efficiency (η) of 6.9%, which is much higher than those of neat TiO2 (4.7%) and Nb-doped TiO2 (5.4%). The enhancement of η is mostly due to the increase of current density, attributed to the improved electron transfer properties including electron injection, collection, and plasmonic effects without the negative effects of charge recombination or problems with corrosion. These properties are supported by intensity modulated photocurrent/voltage spectroscopy (IMPS/IMVS) and incident photon-to-electron conversion efficiency (IPCE) measurements.

  19. Octahedral rotations in strained LaAlO3/SrTiO3 (001 heterostructures

    Directory of Open Access Journals (Sweden)

    T. T. Fister

    2014-02-01

    Full Text Available Many complex oxides display an array of structural instabilities often tied to altered electronic behavior. For oxide heterostructures, several different interfacial effects can dramatically change the nature of these instabilities. Here, we investigate LaAlO3/SrTiO3 (001 heterostructures using synchrotron x-ray scattering. We find that when cooling from high temperature, LaAlO3 transforms from the Pm3¯m to the Imma phase due to strain. Furthermore, the first 4 unit cells of the film adjacent to the substrate exhibit a gradient in rotation angle that can couple with polar displacements in films thinner than that necessary for 2D electron gas formation.

  20. Growing LaAlO3/SrTiO3 interfaces by sputter deposition

    Directory of Open Access Journals (Sweden)

    I. M. Dildar

    2015-06-01

    Full Text Available Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showed the same high degree of epitaxy and atomic order as is made by pulsed laser deposition. However, the high pressure sputtering of oxides is not trivial and number of parameters are needed to be optimized for epitaxial growth. Here we elaborate on the earlier work to show that only a relatively small parameter window exists with respect to oxygen pressure, growth temperature, radiofrequency power supply and target to substrate distance. In particular the sensitivity to oxygen pressure makes it more difficult to vary the oxygen stoichiometry at the interface, yielding it insulating rather than conducting.

  1. Ultrafast Optical Excitation of Coherent and Squeezed Phonons in SrTiO_3

    Science.gov (United States)

    Garrett, G. A.; Whitaker, J. F.; Merlin, R.

    1998-03-01

    We report on the impulsive excitation of coherent and squeezed phonon fields in SrTiO3 using, respectively, first-order and second-order stimulated Raman scattering.(osa.org/oearchive/source/2733.htm>Garrett et al)., Optics Express, to be published. Strontium titanate undergoes an antiferro-distortive phase transition at T_c≈ 110 K to a low temperature tetragonal structure. First-order Raman scattering is allowed only below T_c. Pump-probe spectra were obtained as a function of temperature and pump intensity. The frequency of the coherent (first-order) state is that of the A_1g-component of the soft mode associated with the phase transition. As in KTaO_3,(Garrett et al)., Science 275, 1638 (1997). the squeezed (second-order) field oscillates at a frequency corresponding to a strong, narrow peak in the density of states of the acoustic phonons.

  2. Negative pressure effects in SrTiO 3 nanoparticles investigated by Raman spectroscopy

    Science.gov (United States)

    Wu, XueWei; Wu, DaJian; Liu, XiaoJun

    2008-02-01

    The size effects on SrTiO 3 nanoparticles have been investigated by means of Raman spectroscopy with changing the grain size in the range 10-80 nm. The intensities of the first-order polar TO 2 and TO 4 modes increase as the grain size reduces, suggesting the enhanced interaction of the surface-defect dipoles on the grain boundary. By contrast, the intensities for the first-order nonpolar TO 3 mode decrease with reducing the grain size. Further we have found that the Raman frequencies of the vibration modes are very sensitive to the variation of the grain size. The softening of the TO 2 and TO 3 modes with decreasing the grain size indicates the increase of the Ti-O bond length, which is consistent with the lattice expansion investigated by XRD. We have ascribed the size effects to the negative pressure effects due to the enhanced interaction of the surface-defect dipoles.

  3. Quantum Chemical Study of Water Adsorption on the Surfaces of SrTiO3 Nanotubes.

    Science.gov (United States)

    Bandura, Andrei V; Kuruch, Dmitry D; Evarestov, Robert A

    2015-07-20

    We have studied the adsorption of water molecules on the inner and outer surfaces of nanotubes generated by rolling (001) layers of SrTiO3 cubic crystals. The stability and the atomic and electronic structures of the adsorbed layers are determined by using hybrid density functional theory. The absorption energy and the preferred adsorbate structure are essentially governed by the nature of the surface of the nanotube. Dissociative adsorption prevails on the outer nanotube surfaces. The stability of the adsorbed layers on the inner surfaces is related to the possibility of the formation of hydrogen bonds between water molecules and surface oxygen atoms, and depends on the surface curvature. The presence of water molecules on the inner surface of the nanotubes leads to an increase of the electronic band gap. Externally TiO2 -terminated nanotubes could be used for the photocatalytic decomposition of water by ultraviolet radiation.

  4. Topological states at the (001) surface of SrTiO3

    Science.gov (United States)

    Vivek, Manali; Goerbig, Mark O.; Gabay, Marc

    2017-04-01

    Defect-free SrTiO3 (STO) is a band insulator but angle resolved photoemission spectroscopy (ARPES) experiments have demonstrated the existence of a nanometer thin two-dimensional electron liquid (2DEG) at the (001) oriented surface of this compound. The bulk is a trivial insulator, but our theoretical study reveals that the parity of electronic wave functions in this 2DEG is inverted in the vicinity of special points in reciprocal space where the low-energy dispersion consists of four gapped Dirac cones with a tilted and anisotropic shape. This gives rise to linearly dispersing topological edge states at the one-dimensional boundary. We propose to probe these modes by measuring the Josephson radiation from gapless bound Andreev states in STO based junctions, as it is predicted that they display distinctive signatures of topology.

  5. Resistive switching behavior in single crystal SrTiO3 annealed by laser

    Science.gov (United States)

    Pan, Xinqiang; Shuai, Yao; Wu, Chuangui; Luo, Wenbo; Sun, Xiangyu; Yuan, Ye; Zhou, Shengqiang; Ou, Xin; Zhang, Wanli

    2016-12-01

    Single crystal SrTiO3 (STO) wafers were annealed by XeCl laser (λ = 308 nm) with different fluences of 0.4 J/cm2, 0.6 J/cm2 and 0.8 J/cm2, respectively. Ti/Pt electrodes were sputtered on the surface of STO wafer to form co-planar capacitor-like structures of Pt/Ti/STO/Ti/Pt. Current-Voltage measurements show that the leakage current is enhanced by increasing laser fluence. Resistive switching behavior is only observed in the sample annealed by laser with relatively high fluence after an electro-forming process. The X-ray photoelectron spectroscopy measurements indicate that the amount of oxygen vacancies increases with the increase of laser fluence. This work indicates resistive switching appears when enough oxygen vacancies are generated by the laser, which form conductive filaments under an external electric field.

  6. Dynamic defect correlations dominate activated electronic transport in SrTiO3

    Science.gov (United States)

    Snijders, Paul C.; Şen, Cengiz; McConnell, Michael P.; Ma, Ying-Zhong; May, Andrew F.; Herklotz, Andreas; Wong, Anthony T.; Ward, T. Zac

    2016-07-01

    Strontium titanate (SrTiO3, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. We present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The results show that photo-activated electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. These results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides.

  7. X-ray perfection study of Verneuil-grown SrTiO 3 crystals

    Science.gov (United States)

    Yoshimura, J.; Sakamoto, T.; Usui, S.; Kimura, S.

    1998-07-01

    Dislocations, subgrain textures and other long-range strains in Verneuil-grown SrTiO 3 crystals, used widely as a substrate for growing high- Tc superconducting thin films, have been studied by reflection and transmission X-ray topography to characterize the crystal in regard to structural perfection. It was found that dislocations are nearly aligned along the directions and most of them are of pure edge type, presumably as a property of annealed crystals with simple cubic lattice. This entire dislocation alignment causes a strong long-range distortion about the [0 0 1] axis in anisotropic (1 1 0)-oriented crystal plates. Burgers vectors both of and types were observed. It was also found that the surfaces of some samples were finished highly strain-free as well as optically flat by the mechanochemical polishing.

  8. INTERFACE DISORDER CONTROLLED SUPERCONDUCTIVITY YBa2Cu3O7 / SrTiO3 SUPERLATTICES

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Barriocanal, Javier [Universidad Complutense, Spain; Rivera-Calzada, Alberto [Universidad Complutense, Spain; Sefrioui, Z. [Universidad Complutense, Spain; Arias, D [Universidad Complutense, Spain; Varela del Arco, Maria [ORNL; Leon, C. [Universidad Complutense, Spain; Pennycook, Stephen J [ORNL; Santamaria, J. [Universidad Complutense, Spain

    2013-01-01

    We report on the coherent growth of ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intra-cell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.

  9. First-principles investigations of metal (V, Nb, Ta)-doped monolayer MoS2: Structural stability, electronic properties and adsorption of gas molecules

    Science.gov (United States)

    Zhu, Jia; Zhang, Hui; Tong, Yawen; Zhao, Ling; Zhang, Yongfan; Qiu, Yuzhi; Lin, Xianning

    2017-10-01

    Two-dimensional (2D) layered materials are at the forefront of research because of their unique structures and promising catalytic abilities. Here, the structural stability, electronic properties and gas adsorption of metal (V, Nb, Ta)-doped monolayer MoS2 have been investigated by density functional theory calculations. Our results show that the metal (V, Nb, Ta)-doped monolayer MoS2 is a stable catalyst under room temperature, due to the strong interaction between the doped metals (V, Nb, Ta) and S vacancy of monolayer MoS2. Compared with the gas adsorption (CO, NO2, H2O, NH3) on pristine monolayer MoS2, doped metal (V, Nb, Ta) can significantly improve the adsorption properties, chemical activity and the sensitivity of that of adsorbed gas molecules. This effect occurs due to the strong overlap between the metal nd orbitals and gas molecule orbitals, result in activation of the adsorbed gas molecules. Analysis of Bader charge shows that, more charge transfer (-0.66 e to -0.72 e) occur from metal (V, Nb, Ta)-doped monolayer MoS2 to the oxidizing gas molecules (NO2) acting as acceptors. While for the adsorption of CO molecules, the relative less electrons (about -0.24 e - -0.35 e) transfer occuring from substrate to the adsorbed gases. Whereas the direction of charge transfers is reversed for the adsorption of the reducing gas (H2O and NH3) behaving as donors, in which small electrons (0.04 e -0.09 e) transfer from adsorbed gas to metal (V, Nb, Ta)-doped monolayer MoS2. Our results suggested that metal (V, Nb, Ta)-doped monolayer MoS2 might be a good candidate for low-cost, highly active, and stable catalysts and gas sensors, providing an avenue to facilitate the design of high active MoS2-based two dimensional catalysts and gas sensors.

  10. Effect of Nb and more Fe ions co-doping on the microstructures, magnetic, and piezoelectric properties of Aurivillius Bi5Ti3FeO15 phases

    Science.gov (United States)

    Chen, Chao; Song, Kun; Bai, Wei; Yang, Jing; Zhang, Yuanyuan; Xiang, Pinghua; Qin, Muyang; Tang, Xiaodong; Chu, Junhao

    2016-12-01

    Aurivillius Bi5Ti3-2xFe1+xNbxO15 (BTFNO, x = 0.1, 0.2, 0.3, and 0.4) phases were prepared by solid state reaction method. The structures and dielectric responses were studied, and especially the effects of Nb with a higher valence and more Fe co-doping on the magnetic and piezoelectric properties were addressed in detail. The BTFNO samples were well crystallized with no detectable impurities, and plate-like microstructures with various sizes demonstrate the typical characteristics of bismuth-layer Aurivillius materials. It is found that a dielectric loss peak appears in the Nb and Fe co-doped Bi5Ti3FeO15 (BTFO) ceramics, and it has a shift towards a lower frequency with increasing the Nb doping contents. Furthermore, antiferromagnetic long-range magnetic order is improved with the introduction of Nb and more Fe co-doping. And compared with that of the parent BTFO forms, a clear discrepancy, which is indicative of a super-paramagnetic behavior, of the magnetization vs. temperature curves in zero-field cooling and field cooling cases is observed by the introduction of the Nb and more Fe ions. More interestingly, the introduction of Nb and more Fe ions can suppress the preferred c-axis growth while promoting the a-/b-axis growth of the plate-like grains, and thus favors the piezoelectric behaviors of the BTFO Aurivillius phases along the growth orientation.

  11. Structural evidence for enhanced polarization in a commensurate short-period BaTiO3/SrTiO3 superlattice

    Science.gov (United States)

    Tian, W.; Jiang, J. C.; Pan, X. Q.; Haeni, J. H.; Li, Y. L.; Chen, L. Q.; Schlom, D. G.; Neaton, J. B.; Rabe, K. M.; Jia, Q. X.

    2006-08-01

    A short-period (BaTiO3)6/(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (˜2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c /a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3/SrTiO3 superlattices.

  12. Solid phase epitaxy of EuTiO3 thin films on SrTiO3 (100) substrates with different oxygen contents

    Science.gov (United States)

    Shimamoto, K.; Hirose, Y.; Nakao, S.; Fukumura, T.; Hasegawa, T.

    2013-09-01

    We investigated solid phase epitaxy (SPE) of EuTiO3 thin films on SrTiO3 (100) substrates with different oxygen contents. Amorphous EuTiOx thin films were deposited onto SrTiO3 substrates by pulsed laser deposition and crystallized by subsequent annealing in a vacuum chamber. A pure perovskite EuTiO3 phase was obtained on the reduced (i.e., oxygen-depleted SrTiO3) substrate, while an Eu2Ti2O7 phase was obtained on the oxygen-rich one. These results suggest that oxygen migration occurs between the EuTiOx film and SrTiO3 during SPE. The electric properties of the fabricated EuTiO3 thin films also depended on the amount of oxygen vacancies in the SrTiO3 substrate.

  13. Gate voltage control of the AlO x /SrTiO3 interface electrical properties

    Science.gov (United States)

    Delahaye, J.; Grenet, T.

    2016-10-01

    Electron-beam deposition of an insulating granular aluminium or off-stoichiometric amorphous alumina layer on a SrTiO3 surface is a simple way to get a metallic interface from insulating materials. No heating nor specific preparation of the SrTiO3 surface is needed. In this paper, we investigate how the electrical properties of this interface can be tuned by the use of a back gate voltage (electrical field through the SrTiO3 substrate). We demonstrate that the slow field-effect observed at room temperature can be used to tune in a controlled, reversible way the low temperature electrical properties of the interface. In particular, important parameters of a transistor such as the amplitude of the resistance response to gate voltage changes or the existence of an ‘on’ or an ‘off’ state at zero gate voltage and at low temperature can be adjusted in a single sample. This method should be applicable to any SrTiO3-based interface in which oxygen vacancies are involved and might provide a powerful way to study the metal or superconductor insulator transition observed in such systems.

  14. Photoelectrochemical characteristics of AB5-type hydrogen storage alloy modified with SrTiO3 photocatalyst

    Institute of Scientific and Technical Information of China (English)

    ZHANG Wen-kui; GAN Yong-ping; HUANG Hui; ZHANG Bo; WANG Gai-tian; TU Jiang-ping

    2005-01-01

    Perovskite-type SrTiO3 powders were prepared by using strontium acetate, tetrabutyl titanate and sodium hydroxide via direct hydrolysis-precipitation process. AB5-type hydrogen storage alloy(HSA) electrodes modified with SrTiO3 powders were prepared and the photoelectrochemical characteristics of the as-prepared electrodes were investigated. The results of cyclic voltammograph show that the current of reduction peak increases remarkably under the light irradiation. The obvious photochargeable properties are obtained for the hydrogen storage alloys modified with Perovskite-type SrTiO3 powders. During photocharging process, the potential of the electrode shifts quickly to negative direction and a potential plateau occurs. HSA electrode modified with SrTiO3 powders prepared by direct hydrolysis-precipitation process gives the higher potential of about -0.90 V(vs Hg/HgO) under the light irradiation. SEM observation discloses that a large amount of microcracks occur on the surface of the electrode after photocharging process, which is caused by the formation of hydride in the bulk of electrode.

  15. Evidence of Substrate-Induced Ferroelectric Phase Transition in SrTiO3 by Means of Thermal Measurements

    NARCIS (Netherlands)

    Davitadze, S.; Shnaidshtein, I.; Fadeev, A.; Strukov, B.; Shulman, S.; Noheda, Beatriz; Vlooswijk, A. H. G.

    2010-01-01

    The paper reports the results of the temperature dependence measurements of the specific heat for a SrTiO3 thin (104 nm) film deposited on a DyScO3 substrate. Two anomalies of the specific heat have been observed. They can be associated with the strain-induced ferroelectric phase transition (at 304

  16. The atomic surface structure of SrTiO3 (001) studied with synchrotron X-rays

    NARCIS (Netherlands)

    Vonk, V.; Konings, S.; van Hummel, G.J.; Harkema, Sybolt; Graafsma, H

    2005-01-01

    The atomic surface structure of single terminated SrTiO3(0 0 1) (1 × 1) is investigated employing surface X-ray diffraction. In order to obtain these surfaces a special treatment is needed consisting of chemical etching and annealing. Since this is done in an aqueous and subsequently oxygen

  17. Transport limits in defect-engineered LaAlO3/SrTiO3 bilayers

    NARCIS (Netherlands)

    Gunkel, F.; Wicklein, S.; Hoffmann-Eifert, S.; Meuffels, P.; Brinks, Peter; Huijben, Mark; Waser, R.; Dittmann, R.

    2014-01-01

    The electrical properties of the metallic interface in LaAlO3/SrTiO3 (LAO/STO) bilayers are investigated with focus on the role of cationic defects in thin film STO. Systematic growth-control of the STO thin film cation stoichiometry (defect-engineering) yields a relation between cationic defects in

  18. Magnetocrystalline anisotropy of Fe and Co slabs and clusters on SrTiO3 by first-principles

    DEFF Research Database (Denmark)

    Li, Dongzhe; Barreteau, Cyrille; Smogunov, Alexander

    2016-01-01

    In this paper, we present a detailed theoretical investigation of the electronic and magnetic properties of ferromagnetic slabs and clusters deposited on SrTiO3 via first-principles calculations, with a particular emphasis on the magnetocrystalline anisotropy (MCA). We found that in the case of Fe...

  19. A study by electrical conductivity measurements of the semiconductive and redox properties of Nb-doped NiO catalysts in correlation with the oxidative dehydrogenation of ethane.

    Science.gov (United States)

    Popescu, Ionel; Skoufa, Zinovia; Heracleous, Eleni; Lemonidou, Angeliki; Marcu, Ioan-Cezar

    2015-03-28

    Nb-doped nickel oxides with Nb contents in the range from 1 to 20% and, for comparison, pure NiO, were characterized using in situ electrical conductivity measurements in correlation with their catalytic performances for the oxidative dehydrogenation (ODH) of ethane into ethylene. Their electrical conductivity was studied as a function of temperature and oxygen partial pressure and was followed with time during sequential exposures to air, ethane-air mixture (reaction mixture) and pure ethane in conditions similar to those of catalysis. All the oxides were p-type semiconductors under air. Their electrical conductivity in the reaction temperature range decreased in the following order: NiO > Nb(1)NiO > Nb(5)NiO > Nb(10)NiO > Nb(15)NiO > Nb(20)NiO. This correlates well with the catalytic activity expressed as the intrinsic rate of ethane consumption. All the catalysts were partially reduced under the reaction mixture in the reaction temperature range, an inverse correlation between their conductivity in these conditions and the ODH selectivity being observed. The ODH reaction of ethane takes place via a heterogeneous redox mechanism involving the surface lattice O(-) species.

  20. Electro-optic coefficients r13 and r33 of singly Er3+-doped and In3+/Er3+-codoped LiNbO3 crystals

    Science.gov (United States)

    Du, Wan-Ying; Zhang, Pei; Zhang, Zi-Bo; Ren, Shuai; Wong, Wing-Han; Yu, Dao-Yin; Pun, Edwin Yue-Bun; Zhang, De-Long

    2017-01-01

    A series of singly Er3+-doped and doubly In3+/Er3+-doped congruent LiNbO3 crystals were grown by Czochralski method. The Er3+-only doped crystals were grown from the growth melts doped with different concentrations of Er2O3 up to 1 mol%, and the In3+/Er3+-codoped crystals from the melts doped with fixed 0.5 mol% Er2O3 while varied In2O3 contents of 0.0, 0.5, 1.0 and 1.5 mol%. The electro-optic coefficients γ13 and γ33 of these doped crystals were measured by Mach-Zehnder interferometry. Both clamped and unclamped coefficients were measured. The results show that both γ13 and γ33 reveal small Er3+ and In3+ doping effects. In the Er3+-only doping case, γ13 almost does not change within the experimental error of 3%, γ33 reveals a degradation tendency with a rise in Er3+ doping level, but the degradation is no more than 5% in the considered Er3+ concentration range 0-3.0 mol% (in crystal). In the In3+/Er3+-codoping case, both γ13 and γ33 can be regarded as unchanged in the studied In3+ concentration range of 0-2.6 mol% (in crystal) within the error. The small Er3+ or In3+ doping effect is desired in light of electro-optic application of these crystals. It is qualitatively explained on the basis of EO coefficient model and doping effect on defect structure of LiNbO3.

  1. Structure and photocatalytic properties of Nb-doped Bi{sub 12}TiO{sub 20} prepared by the oxidant peroxide method (OPM)

    Energy Technology Data Exchange (ETDEWEB)

    Nogueira, André E., E-mail: andreesteves86@hotmail.com; Lima, Alan R. F., E-mail: alan_rogerio2000@yahoo.com.br [UFSCar-Universidade Federal de São Carlos, LIEC-Laboratório Interdisciplinar de Eletroquímica e Cerâmica, Departamento de Química (Brazil); Longo, Elson, E-mail: elson@iq.unesp.br [UNESP-Universidade Estadual Paulista, Instituto de Química de Araraquara (Brazil); Leite, Edson R., E-mail: edson.leite@pq.cnpq.br; Camargo, Emerson R., E-mail: camargo@ufscar.br [UFSCar-Universidade Federal de São Carlos, LIEC-Laboratório Interdisciplinar de Eletroquímica e Cerâmica, Departamento de Química (Brazil)

    2014-12-15

    Pure (Bi{sub 12}TiO{sub 20}) and niobium-doped (Bi{sub 12}Ti{sub 1−x}Nb{sub x}O{sub 20}, with “x” up to 0.15) bismuth titanates were prepared by the oxidant peroxide method (OPM) and used to photodegradate rhodamine b (RhB) under UV and visible radiation. Rietveld refinements showed samples consisting mainly of sillenite structure with small amounts of a perovskite secondary phase in the Nb-doped materials. These bismuth-based catalysts exhibited superior performance than the commercial TiO{sub 2}, with band gaps ranging from 2.53 of pure Bi{sub 12}TiO{sub 20} to 2.73 eV depending on the amount of niobium added, which seems to be responsible for the improved photoactivity of the doped catalysts under UV radiation.

  2. High-temperature defect structure of Nb-doped LaCrO sub 3

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Chikung J.; Anderson, H.U.; Sparlin, D.M. (Univ. of Missouri, Rolla (USA))

    1989-02-01

    Electrical conductivity and Seebeck measurements on LaCr{sup 0.98}Nb{sub 0.02}CrO{sub 3} show that the defect structure of the material is mainly controlled by the extrinsic electrons formed by the Nb donors through the electronic compensation process. The experimental results also indicate that this material conducts electricity via a small polaron mechanism with an electron mobility around 0.004-0.01 cm{sup 2}/v sec between 1100 and 1300{degree}C. 8 refs., 10 figs.

  3. Effect of CeO2 on Electrical Properties of (Nb,Mn)-Doped TiO2 Varistor Ceramics

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The electrical properties of TiO2-based varistor ceramics with different amount of CeO2 were investigated by measuring the properties of V-I, permittivity, density and boundary defect barriers. It is found that an optimal composition doped with 0.7% CeO2 exhibits the highest nonlinear coefficient of 10.5, the highest breakdown voltage of 12.77consistent with the highest and narrowest grain-boundary defect barriers. In order to illustrate the grain boundary barriers formation in TiO2-Nb2O5-MnCO3-CeO2 varistor, an grain-boundary defect barrier model was also introduced.

  4. Pack cementation Cr-Al coating of steels and Ge-doped silicide coating of Cr-Nb alloy

    Energy Technology Data Exchange (ETDEWEB)

    He, Y.R.; Zheng, M.H.; Rapp, R.A. [Ohio State Univ., Columbus, OH (United States)

    1995-08-01

    Carbon steels or low-alloy steels used in utility boilers, heat exchangers, petrochemical plants and coal gasification systems are subjected to high temperature corrosion attack such as oxidation, sulfidation and hot corrosion. The pack cementation coating process has proven to be an economical and effective method to enhance the corrosion resistance by modifying the surface composition of steels. With the aid of a computer program, STEPSOL, pack cementation conditions to produce a ferrite Cr-Al diffusion coating on carbon-containing steels by using elemental Cr and Al powders have been calculated and experimentally verified. The cyclic oxidation kinetics for the Cr-Al coated steels are presented. Chromium silicide can maintain high oxidation resistance up to 1100{degrees}C by forming a SiO{sub 2} protective scale. Previous studies at Ohio State University have shown that the cyclic oxidation resistance of MOSi{sub 2} and TiSi{sub 2} can be further improved by Ge addition introduced during coating growth. The halide-activated pack cementation process was modified to produce a Ge-doped silicide diffusion coating in a single processing step for the ORNL-developed Cr-Nb advanced intermetallic alloy. The oxidation behavior of the silicide-coated Cr-Nb alloy was excellent: weight gain of about 1 mg/cm{sup 2} upon oxidation at 1100{degrees}C in air for 100 hours.

  5. Dielectric relaxation and localized electron hopping in colossal dielectric (Nb,In)-doped TiO2 rutile nanoceramics.

    Science.gov (United States)

    Tsuji, Kosuke; Han, HyukSu; Guillemet-Fritsch, Sophie; Randall, Clive A

    2017-03-28

    Dielectric spectroscopy was performed on a Nb and In co-doped rutile TiO2 nano-crystalline ceramic (n-NITO) synthesized by a low-temperature spark plasma sintering (SPS) technique. The dielectric properties of the n-NITO were not largely affected by the metal electrode contacts. Huge dielectric relaxation was observed at a very low temperature below 35 K. Both the activation energy and relaxation time suggested that the electronic hopping motion is the underlying mechanism responsible for the colossal dielectric permittivity (CP) and its relaxation, instead of the internal barrier layer effect or a dipolar relaxation. With Havriliak-Negami (H-N) fitting, a relaxation time with a large distribution of dielectric relaxations was revealed. The broad distributed relaxation phenomena indicated that Nb and In were involved, controlling the dielectric relaxation by modifying the polarization mechanism and localized states. The associated distribution function is calculated and presented. The frequency-dependent a.c. conductance is successfully explained by a hopping conduction model of the localized electrons with the distribution function. It is demonstrated that the dielectric relaxation is strongly correlated with the hopping electrons in the localized states. The CP in SPS n-NITO is then ascribed to a hopping polarization.

  6. 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.

  7. 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.

  8. 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.

  9. Interface-enhanced sensitivity of photoconductivity to the electric current and magnetic field in La0.67Ca0.33MnO3/Nb-SrTiO3 p-n junctions

    Science.gov (United States)

    Wang, S.; Ma, Z. Z.; Xiong, J. J.; Li, C. J.; Hou, Y. H.; Ma, T. X.; Xiong, C. M.; Dou, R. F.; Nie, J. C.

    2016-12-01

    The effects of electric current and magnetic field on the photoconductivity (PC) of La0.67Ca0.33MnO3 (LCMO) films have been investigated within a comparative study on LCMO films on an n-type semiconducting Nb-doped SrTiO3 (NSTO) and insulating SrTiO3 (STO) substrates separately. At room temperature, LCMO on NSTO (LCMO/NSTO) was found to show remarkable PC effect than that on STO (LCMO/STO). More attractive is that, compared with that of LCMO/STO, the room-temperature PC of LCMO/NSTO also shows a high sensitivity to the change of current or magnetic field: for LCMO/NSTO under a light illumination with an intensity of 60 mW/cm2, the increment of current yields a decreases of PC at a rate of 7.6%/μA, while an application of magnetic field of 1.2 T can suppress PC by a percentage as high as ˜20%. In contrast, under the same stimulus of current or field, PC of LCMO/STO remains almost unchanged. The phenomena can be explained based on the interface effects correlated with the photocarrier injection, current shunting, and magnetic tunability occurred at the interface. This work demonstrates that manganite-based heterojunctions with interface engineering are promising for developing a new type of photoelectric device with high sensitivity and multifunctionality.

  10. Investigation of Mechanism of Co-doped Zn2+ and In3+ Influence on Optical Properties of Fe∶LiNbO3

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Doping Zn with the concentration of 3mol% and In2O3 with different concentrations in Fe∶LiNbO3, Zn∶In∶Fe∶LiNbO3 crystals were grown. The infrared spectra of the crystals were measured and the mechanism of the OH-, absorption peak shifting was studied. The diffraction efficiency, response time and photoconduction of the crystals were measured. The mechanisms of the photoconduction increasing, diffraction efficiency decreasing and response time shorting for those crystals were studied.

  11. Lasing effects in new Nd3+-doped TeO2-Nb2O5-WO3 bulk glasses

    Science.gov (United States)

    Carreaud, J.; Labruyère, A.; Dardar, H.; Moisy, F.; Duclère, J.-R.; Couderc, V.; Bertrand, A.; Dutreilh-Colas, M.; Delaizir, G.; Hayakawa, T.; Crunteanu, A.; Thomas, P.

    2015-09-01

    This paper demonstrates for the first time continuous wave (cw) and pulsed lasing effects in a 75TeO2-20NbO2.5-5WO3 glass doped with 1 mol.% in Nd3+. It is divided into two parts: The first part treats all the aspects related to the elaboration and the characterization of the materials. Thus, glasses elaborated within the TeO2-Nb2O5-WO3 ternary system show a rather high glass transition temperature Tg ∼ 375 °C, with an excellent thermal stability of ∼160 °C. Compared to glasses synthesized in either TeO2-Nb2O5 or TeO2-WO3 binary systems, glasses fabricated within such system show improved mechanical performances, with larger Young's modulus values. The structural characteristics of the samples, studied by Raman spectroscopy, are also presented. Linear optical properties (refractive index and extinction coefficient) are accessed by spectroscopic ellipsometry. As well, the optical transmission of the various bulk glasses is measured, in the case of both uncoated and coated glasses. In particular, specific anti-reflective coatings at 808 nm (laser diode pump wavelength) and 1064 nm (laser emission wavelength) are respectively deposited on the two surfaces of the sample in order to minimize the losses due to Fresnel reflections at the two glass/air interfaces. In addition, another specific surface treatment (Rmax at 1064 nm) was employed to serve as the back mirror of the laser cavity. The optical transmission data testified to the real efficiency of all these coatings. Finally, the photoluminescence properties (emission and excitation spectra, and luminescence decay curve) of the Nd3+-doped glasses, measured at room temperature for bulk samples, and as a function of temperature for powder glasses, are discussed. The second part is focused on evidencing (cw) and pulsed lasing effects in such coated bulk lasers. Cylindric samples of only a few millimeters in height and in diameter were tested and led to a laser emission around 1064 nm, characterized by a very low

  12. Fabrication and Photocatalytic Property of One-Dimensional SrTiO3/TiO2-xNx Nanostructures

    Directory of Open Access Journals (Sweden)

    Huarong Zhang

    2013-01-01

    Full Text Available One-dimensional SrTiO3/TiO2−xNx nanostructures were prepared by the hydrothermal method and investigated by X-ray diffraction (XRD, transmission electron microscopy (TEM, X-ray photoelectron spectroscopy (XPS, and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS measurements. The photocatalytic activities of the prepared samples were evaluated by photodegrading the methylene blue (MB solution. According to the characterizations, the intermediate product of SrTiO3/titanate nanotubes was presented after hydrothermal processing of the TiO2−xNx nanoparticles with the mixed solution of NaOH and Sr(NO32. The final product of SrTiO3/TiO2−xNx nanorods was obtained after calcining the intermediate. As compared to the TiO2−xNx nanoparticles, the absorption performance of SrTiO3/titanate nanotubes or SrTiO3/TiO2−xNx nanorods was depressed, instead of improving it. The mechanisms of the absorption property changes were discussed. The SrTiO3/TiO2−xNx nanorods presented better photocatalytic activity than the TiO2−xNx nanoparticles or nanorods. However, due to overmuch adsorption, the SrTiO3/titanate nanotubes gave ordinary photocatalytic performances.

  13. Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

    Institute of Scientific and Technical Information of China (English)

    LIU Guang-Tong; JIN Hao; LI Zheng; GENG Hong-Xia; CHE Guang-Can; JIN Duo; SUN Lian-Feng; XIE Si-Shen; LUO Jian-Lin

    2008-01-01

    We have performed low temperature resistivity p(T) and specific heat C(T) measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample.The results indicate that the superconducting transition temperature is ~4.6 K.The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe.The electronic coefficient of specific heat γn=4.51 mJ mol-1 K2 and the Debye temperature θn=419 K are obtained by fitting the zero-field specific heat data in the normal state.At low temperatures,the electronic specific heat in the superconducting state follows Ces/γnTc=2.84 exp(-1.21Tc/T).This indicates that the superconducting pairing in Nb0.75Mg0.25 B2 has s-wave symmetry.

  14. Origin of in Situ Domain Formation of Heavily Nb-Doped Pb(Zr,Ti)O3 Thin Films Sputtered on Ir/TiW/SiO2/Si Substrates for Mobile Sensor Applications.

    Science.gov (United States)

    Han, Chan Su; Park, Kyu Sik; Choi, Hong Je; Cho, Yong Soo

    2017-06-07

    High-quality piezoelectric thin films have recently been in demand for mobile sensor applications. An investigation was conducted to understand the improvements in the piezoelectric and imprint characteristics of heavily Nb-doped lead zirconate titanate thin films with an extensive range of Nb content (up to 14 mol %) beyond the typical solid solubility limit of Nb. The positive effects produced by the unusual doping of Nb were realized by utilizing an in situ sputtering process that did not require a subsequent annealing and poling procedure. An enhanced piezoelectric coefficient, -e31, of -12.87 C/m(2) and a stronger shift in the coercive field, Ec,shift, of ∼20 kV/cm, which are ideally useful for mobile sensor applications, were obtained for the 12 mol % Nb-doped films deposited on nonconventional buffer electrodes of Ir/TiW. The reduced oxygen vacancy concentration and preferred domain orientation with a stronger piezoresponse induced by the Nb donor doping contributed to the enhancement of the piezoelectric properties. Potential defect dipoles aligned by a residual stress gradient along columnar structures seemed to induce an internal electric field in the Nb-doped films, leading to the preferred domain orientation, as well as the strong imprint behavior due to a clamping of domain walls.

  15. Polaronic metal state at the LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Cancellieri, C.; Mishchenko, A. S.; Aschauer, U.; Filippetti, A.; Faber, C.; Barišić, O. S.; Rogalev, V. A.; Schmitt, T.; Nagaosa, N.; Strocov, V. N.

    2016-01-01

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

  16. Surface morphology determined by (0 0 1) single-crystal SrTiO 3 termination

    Science.gov (United States)

    Koster, Gertjan; Rijnders, Guus; Blank, Dave H. A.; Rogalla, Horst

    2000-11-01

    The terminating layer of a perovskite (0 0 1) ABO 3 crystal, with A as an alkaline earth metal and B as a transition metal, influences the characteristics of the surface. The morphology during thermal treatment of the surface and epitaxial growth are determined by the composition of the surface, i.e., whether it is BO 2, AO, or a mixed-terminated surface. Since the morphology of a thin film is the result of the evolution of the surface during deposition, control from the very first layer is essential for smooth films. In the case of perovskite materials, this means control of the terminating layer. Here, we study the SrTiO 3 surface as a model system and the effects of the composition of the terminating layer, determined by the treatment and/or deposition of SrO and TiO 2, on homo-epitaxial and hetero-epitaxial growth of SrCuO 2 and YBa 2Cu 3O 7. A single-terminated surface turns out to be optimal with respect to a smooth morphology and perfect epitaxy of high- Tc superconducting materials.

  17. Anomalous conductivity, Hall factor, magnetoresistance, and thermopower of accumulation layer in SrTiO3

    Science.gov (United States)

    Fu, Han; Reich, K. V.; Shklovskii, B. I.

    2016-07-01

    We study the low temperature conductivity of the electron accumulation layer induced by the very strong electric field at the surface of an SrTiO3 sample. Due to the strongly nonlinear lattice dielectric response, the three-dimensional density of electrons n (x ) in such a layer decays with the distance from the surface x very slowly as n (x ) ∝1 /x12 /7 . We show that when the mobility is limited by the surface scattering the contribution of such a tail to the conductivity diverges at large x because of growing time electrons need to reach the surface. We explore truncation of this divergence by the finite sample width, by the bulk scattering rate, by the back gate voltage, or by the crossover to the bulk linear dielectric response with the dielectric constant κ . As a result we arrive at the anomalously large mobility, which depends not only on the rate of the surface scattering, but also on the physics of truncation. Similar anomalous behavior is found for the Hall factor, the magnetoresistance, and the thermopower.

  18. Oxygen vacancies at the surface of SrTiO3 thin films

    Science.gov (United States)

    Silva, Alexandre R.; Dalpian, Gustavo M.

    2013-03-01

    The 2-D electron gas at the interface between LaAlO3 (LAO) and SrTiO3 (STO), two band insulators, has been the subject of intense research owing to the fact that this interface can show metallic, superconducting, and magnetic effects, properties that are absent in the bulk counterparts. The metallic behavior has also been observed at the STO surface, without the need of the oxides' interface. Although the reason of this behavior is not well defined, there are three hypotheses for this: the polar catastrophe; the oxygen vacancies produced in the experiment, and cations intermixing. In this work, first principles calculations based on the density functional theory and using hybrid functionals were performed to reveal the atomic and the electronic structure of vacancies at the (001) surface of STO films. We have analyzed both the TiO2 and SrO-terminated surfaces. For pure surfaces, we observed atomic relaxations up to the 5th atomic layer. The surface band structure of ideal STO slabs shows that the STO thin films are insulating in both terminations, but insert surface levels in the gap of bulk STO. Defective STO slabs are observed to be metallic, and we observe a strong tendency for the oxygen vacancies to migrate into the surface. We thank financial support from brazilian agencies CAPES, CNPq and FAPESP.

  19. Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO3

    Science.gov (United States)

    Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.; Lee, Ho Nyung; Christen, H. M.; Zschack, P.; Larson, B. C.

    2016-11-01

    We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO3 . We show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing in PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD "self-organizes" local step flow on a length scale consistent with the substrate temperature and PLD parameters.

  20. Anomalous behavior of B{sub 1g} mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

    Energy Technology Data Exchange (ETDEWEB)

    Gautam, Subodh K., E-mail: subodhkgtm@gmail.com, E-mail: fouran@gmail.com; Ojha, S.; Singh, Fouran, E-mail: subodhkgtm@gmail.com, E-mail: fouran@gmail.com [Material Science Group, Inter University Accelerator Centre, New Delhi -110067 (India); Gautam, Naina [Department of Electronic Science, University of Delhi South Campus, New Delhi - 110023 (India); Singh, R. G. [Department of Physics, Bhagini Nivedita College, Delhi University, Delhi– 110043 (India); Shukla, D. K. [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017 (India)

    2015-12-15

    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 TiO{sub 2} 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{sup +5} in the TiO{sub 2} 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{sup −1} for the E{sub g(1)} mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B{sub 1g} mode exhibits a large anomalous softening of 20 cm{sup −1} with asymmetrical broadening; which was not reported for the case of pure TiO{sub 2} crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb{sup 5+} doping induced reduction of Ti{sup 4+} 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.

  1. Synthesis, crystal structure and EPR studies of vanadyl doped [Co(2-nbH)2(ina)2(H2O)] complex

    Science.gov (United States)

    Bozkurt, Esat; Çelik, Yunus; Çöpür, Fatma; Dege, Necmi; Topcu, Yıldıray; Karabulut, Bünyamin

    2016-08-01

    A novel aquabis(isonicotinamide-κN1)bis(2-nitrobenzoato-κ2O,O‧;κO)cobalt(II), (hereafter [Co(2-nbH)2(ina)2(H2O)]; 2-nbH: 2-nitrobenzoic acid; ina: isonicotinamide), complex was synthesized and characterized by using various techniques. The crystal structure was determined by X-ray diffraction (XRD) method. The magnetic properties of VO2+ doped [Co(2-nbH)2(ina)2(H2O)] complex were obtained by electron paramagnetic resonance (EPR) technique. The angular variation of EPR spectra shows that two different VO2+ complexes are present in the lattice. The FT-IR spectra of this compound were discussed in relation to other compounds containing 2-nitrobenzoato or isonicotinamide ligands. Thermal stability and reactivity of this complex were also studied by thermal analysis methods (TG/DTG/DTA).

  2. Micrometer-Scale Ballistic Transport of Electron Pairs in LaAlO3/SrTiO3 Nanowires

    Science.gov (United States)

    Tomczyk, Michelle; Cheng, Guanglei; Lee, Hyungwoo; Lu, Shicheng; Annadi, Anil; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Eom, Chang-Beom; Levy, Jeremy

    2016-08-01

    High-mobility complex-oxide heterostructures and nanostructures offer new opportunities for extending the paradigm of quantum transport beyond the realm of traditional III-V or carbon-based materials. Recent quantum transport investigations with LaAlO3/SrTiO3 -based quantum dots reveal the existence of a strongly correlated phase in which electrons form spin-singlet pairs without becoming superconducting. Here, we report evidence for the micrometer-scale ballistic transport of electron pairs in quasi-1D LaAlO3/SrTiO3 nanowire cavities. In the paired phase, Fabry-Perot-like quantum interference is observed, in sync with conductance oscillations observed in the superconducting regime (at a zero magnetic field). Above a critical magnetic field Bp, the electron pairs unbind and the conductance oscillations shift with the magnetic field. These experimental observations extend the regime of ballistic electronic transport to strongly correlated phases.

  3. In-situ monitor of insulator to metal transition in SrTiO3 by Ar+ irradiation

    Science.gov (United States)

    Wang, Qiuru; Zhang, Wanli; Zhang, Wenxu; Zeng, Huizhong

    2016-03-01

    Metallic conduction layer produced by the irradiation of the SrTiO3 surface is an intriguing phenomenon, where the process and mechanism of the insulating to conducting transition are still under debate. We have studied the influence of argon ion bombardment on the SrTiO3 (STO) single crystal by X-ray Photoelectron Spectroscopy (XPS) and Photoluminescence (PL). The former demonstrated the existence of a lower oxidation state of Ti, which implied oxygen vacancies were present at the near-surface region. The latter showed that the oxygen damage enhanced with increasing irradiation time, and decreased by annealing in oxygen at high temperature. The in-situ electrical conductance measurement during irradiation revealed the correlation between the resistance of ion-irradiated STO and the irradiation time. The existence of sufficient amount of oxygen vacancies was proposed to be responsible to the insulator to metal transition during the process of irradiation.

  4. Growth and Characterization of EuTiO3 films on SrTiO3 (001)

    Science.gov (United States)

    Wang, H. Q.; Ferguson, J. D.; Woll, A. R.; Muller, D. A.; Brock, J. D.

    2009-03-01

    Perovskite oxides display a variety of interesting physical properties, and their heteroepitaxial structures are of significant interest in oxide electronics. EuTiO3 and SrTiO3 are nearly perfectly lattice matched and have the same valence structure, and are therefore well suited as a model system for the study of perovskite interfaces. One outstanding question about such interfaces concerns the factors that determine and limit atomic and electronic abruptness. In this work, several monolayer thick EuTiO3 films are grown on single-crystal SrTiO3 (001) substrates using Pulsed Laser Deposition (PLD). The growth mechanisms are probed by the combination of synchrotron based in situ small angle x-ray scattering (SAXS) and in situ Reflection High Energy Electron Diffraction (RHEED). The atomic-scale interfacial properties are investigated by high resolution Scanning Transmission Electron Microscopy (STEM) and spatially resolved Electron Energy Loss Spectroscopy (EELS).

  5. Predictive model based on artificial neural net for purity of perovskite-type SrTiO3 nanocrystalline

    Institute of Scientific and Technical Information of China (English)

    REN Qing-li; CAO Quan-xi

    2006-01-01

    A three-layer structure back-propagation network model based on the non-linear relationship between the purity of the perovskite-type SrTiO3 nano-crystal samples and the technology factors,such as reaction time,reaction temperature,raw material adding amount of NaOH and SrCl2,and the rate of TiCl4/Hl,was established. The input variables were pretreated by using the main component analysis firstly. Moreover,the momentum terms were introduced so as to accelerate the converging rate and avoid the non-converging situation. At the same time,the variable learning speed was adopted. The results show that the improved back propagation neural network model is very efficient for the prediction of the perovskite-type SrTiO3 nano-crystal sample purity.

  6. Disordered ferroelectricity in the PbTiO3/SrTiO3 superlattice thin film

    Science.gov (United States)

    Kim, Gi-Yeop; Chu, Kanghyun; Sung, Kil-Dong; Lee, Hak-Sung; Kim, Sung-Dae; Song, Kyung; Choi, Taekjib; Lee, Jaichan; Buban, James P.; Yoon, Seog-Young; Kim, Kwang-Ho; Yang, Chan-Ho; Choi, Si-Young

    2017-06-01

    The PbTiO3/SrTiO3 superlattice thin films with a low volume fraction of PbTiO3 have not attracted much interest because they are thought to exhibit only a paraelectric state. In this study, we focus on a superlattice thin film with thin PbTiO3 (PTO) and thick SrTiO3 (STO) layers, wherein the hidden ferroelectricity in the thin PbTiO3 layer is revealed. Atomic scale imaging analysis and electron energy loss spectroscopy reveal the existence of a disordered ferroelectric polarization state without innate tetragonal distortion in the (6PTO/15STO)5 superlattice. The piezoelectric force microscopy analysis confirms that this disordered ferroelectricity can enhance piezoelectric response.

  7. Properties of Nb-doped ZnO transparent conductive thin films deposited by rf magnetron sputtering using a high quality ceramic target

    Indian Academy of Sciences (India)

    J W Xu; H Wang; M H Jiang; X Y Liu

    2010-04-01

    Nb-doped ZnO films with (002) orientation have been grown on glass substrates by rf magnetron sputtering followed by vacuum annealing at 400°C for 3 h. The microstructures and surface figures of the Nbdoped ZnO films were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. And its optical and electrical properties were measured at room temperature using a four-point probe technique and 756-type spectrophotometer, respectively. X-ray diffraction (XRD) revealed that the films are highly textured along the axis and perpendicular to the surface of the substrate. After annealing at 400°C for 180 min under vacuum, transmittance of about 90% in visible region for Nb doped ZnO films was confirmed by the optical transmission spectra, and the low resistivity of 5.47 × 10-3 .cm was obtained.

  8. Electrical and microstructural properties of CaTiO3-doped K1/2Na1/2NbO3-lead free ceramics

    Indian Academy of Sciences (India)

    L Ramajo; R Parra; M A Ramírez; M S Castro

    2011-10-01

    Microstructure, electrical properties and dielectric behaviour of K1/2Na1/2NbO3 (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 detected. It was also observed that CTO changed the microstructure and grain size of KNN drastically. Also, the Curie temperature and permittivity values decreased. Addition of CTO between 0.15 and 0.45 mol% decreases the density and dielectric values. Samples prepared with higher content of CTO than 0.45 mol% showed better electrical properties.

  9. High electrostrictive strain induced by defect dipoles in acceptor-doped (K0.5Na0.5)NbO3 ceramics

    Science.gov (United States)

    Dai, Ye-Jing; Zhao, Yong-Jie; Zhao, Zhe; Zhao, Zhi-Hao; Zhou, Qi-Wu; Zhang, Xiao-Wen

    2016-07-01

    Acceptor doping is an efficient method to improve ferroelectric material performance through the formation of defect dipoles. Here, a high electrostrictive strain of 0.16-0.19%, and large d33\\ast of  >300 pm V-1 are obtained in CuO-doped (K0.5Na0.5)NbO3 ceramics. We analyzed the orientation relationship and the interaction between defect dipole polarization (P d) along orientation and spontaneous polarization (P s) parallel to in orthorhombic (K0.5Na0.5)NbO3. Thus, a ‘coupling effect’ mechanism was suggested to explain how the P d and P s can work together to contribute to the electrostrictive strains in this lead-free piezoelectric ceramic.

  10. 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.

  11. Analysis of local conductance switching by AFM-writing at the LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Boselli, Margherita; Li, Danfeng; Liu, Wei; Fête, Alexandre; Gariglio, Stefano; Triscone, Jean-Marc

    2015-03-01

    A two dimensional electron liquid is present at the interface between LaAlO3 and SrTiO3; this system exhibits several interesting physical properties, including tunable superconductivity. In heterostructures with 3 unit cells of LaAlO3, an insulator to metal transition can be induced by the electric field effect. We report here on the use of the atomic force microscopy writing technique developed in the group of J. Levy to locally switch on and off conductivity at the interface. Our results show that a quarz resonator AFM sensor is particularly suitable for this purpose. In this configuration, the measurements can be performed in the dark, strongly reducing photo-doping. Electronic nanostructures are found to be particularly sensitive to the writing procedure and to the ambient humidity. We discuss how these parameters can be optimized to confine electrons in regions down to tens of nanometers. Simulations of the conductance changes upon AFM writing are compared to experiments. The temperature evolution of the conductance shows that nanowires are metallic.

  12. Room-Temperature Quantum Transport Signatures in Graphene/LaAlO3 /SrTiO3 Heterostructures.

    Science.gov (United States)

    Jnawali, Giriraj; Huang, Mengchen; Hsu, Jen-Feng; Lee, Hyungwoo; Lee, Jung-Woo; Irvin, Patrick; Eom, Chang-Beom; D'Urso, Brian; Levy, Jeremy

    2017-03-01

    High mobility graphene field-effect devices, fabricated on the complex-oxide heterostructure LaAlO3 /SrTiO3 , exhibit quantum interference signatures up to room temperature. The oxide material is believed to play a critical role in suppressing short-range and phonon contributions to scattering. The ability to maintain pseudospin coherence at room temperature holds promise for the realization of new classical and quantum information technologies.

  13. 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.

  14. Morphology and Luminescence of Nanocrystalline Nb2O5 Doped with Eu3+

    Directory of Open Access Journals (Sweden)

    Daniele Falcomer

    2007-01-01

    Full Text Available The synthesis of nanocrystalline Nb2O5:Eu3+ has been achieved by using a Pechini procedure. The obtained materials are single-phase niobia with the orthorhombic structure, average crystallite size around 25 nm and average lattice strain of about 0.002. TEM images show that the particles are rectangular and reasonably isolated. The luminescence of the Eu3+ ions in the niobia lattice is efficient and affected by a strong inhomogeneous broadening, due to an important disorder around the lanthanide ions.

  15. Nano-sized Mo- and Nb-doped TiO2 as anode materials for high energy and high power hybrid Li-ion capacitors

    Science.gov (United States)

    Bauer, Dustin; Roberts, Alexander J.; Matsumi, Noriyoshi; Darr, Jawwad A.

    2017-05-01

    Nano-sized Mo-doped titania (Mo0.1Ti0.9O2) and Nb-doped titania (Nb0.25Ti0.75O2) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO2 negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5-3.0 V, the Mo0.1Ti0.9O2/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg-1 at a power of 180 W kg-1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb0.25Ti0.75O2/AC hybrid supercapacitor maintained its energy density of 45 Wh kg-1 at 180 W kg-1 better, showing 36 Wh g-1 at 3200 W kg-1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0-3.0 V led to an increase in power density, with the Mo0.1Ti0.9O2/AC hybrid supercapacitor giving energy densities of 12 Wh kg-1 and 2.5 Wh kg-1 at power densities of 6700 W kg-1 and 14 000 W kg-1, respectively.

  16. Light induced suppression of Kondo effect at amorphous LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Liu, G. Z.; Qiu, J.; Jiang, Y. C.; Zhao, R.; Yao, J. L.; Zhao, M.; Feng, Y.; Gao, J.

    2016-07-01

    We report photoelectric properties of two-dimensional electron gas (2DEG) at an amorphous LaAlO3/SrTiO3 interface. Under visible light illumination (650 nm), an enhancement of electric conductivity is observed over the temperature range from 2 to 300 K. Particularly, a resistance upturn appearing below 25 K, which is further proved to from the Kondo effect, is suppressed by the 650 nm visible light. From the results of light-assisted Hall measurements, light irradiation increases the carrier mobility rather than carrier density in the Kondo regime. It is suggested that light induces the decoherence effect of localized spin states, hence the electron scattering is weakened and the carrier mobility is improved accordingly. Moreover, the enhancement of electrical conductivity by visible light verifies that in-gap states located in the SrTiO3 side of the interface play an important role in the electrical transport of the amorphous SrTiO3-based oxide 2DEG system. Our results provide deeper insight into the photoinduced effects in the 2DEG system, paving the way for the design of optoelectronic devices based on oxides.

  17. The interface of SrTiO3 and H2O from density functional theory molecular dynamics

    Science.gov (United States)

    Holmström, E.; Spijker, P.; Foster, A. S.

    2016-09-01

    We use dispersion-corrected density functional theory molecular dynamics simulations to predict the ionic, electronic and vibrational properties of the SrTiO3/H2O solid-liquid interface. Approximately 50% of surface oxygens on the planar SrO termination are hydroxylated at all studied levels of water coverage, the corresponding number being 15% for the planar TiO2 termination and 5% on the stepped TiO2-terminated surface. The lateral ordering of the hydration structure is largely controlled by covalent-like surface cation to H2O bonding and surface corrugation. We find a featureless electronic density of states in and around the band gap energy region at the solid-liquid interface. The vibrational spectrum indicates redshifting of the O-H stretching band due to surface-to-liquid hydrogen bonding and blueshifting due to high-frequency stretching vibrations of OH fragments within the liquid, as well as strong suppression of the OH stretching band on the stepped surface. We find highly varying rates of proton transfer above different SrTiO3 surfaces, owing to differences in hydrogen bond strength and the degree of dissociation of incident water. Trends in proton dynamics and the mode of H2O adsorption among studied surfaces can be explained by the differential ionicity of the Ti-O and Sr-O bonds in the SrTiO3 crystal.

  18. Synthesis of crystalline perovskite-structured SrTiO3 nanoparticles using an alkali hydrothermal process

    Institute of Scientific and Technical Information of China (English)

    U.K.N. Din; T.H.T. Aziz; M.M. Salleh; A.A. Umar

    2016-01-01

    We report an experimental route for synthesizing perovskite-structured strontium titanate (SrTiO3) nanocubes using an alkali hydrothermal process at low temperatures without further heating. Furthermore, we studied the influence of heating time (at 180°C) on the crystallinity, morphology, and perovskite phase formation of SrTiO3. The SrTiO3 powder, which is formed via nanocube agglomeration, transforms into cubic particles with a particle size of 120–150 nm after 6 h of hydrothermal sintering. The crystallinity and percentage of the perovskite phase in the product increased with heating time. The cubic particles contained 31.24at% anatase TiO2 that originated from the precursor. By varying the weight ratio of anatase TiO2 used to react with the strontium salt precursor, we reduced the anatase-TiO2 content to 18.8at%. However, the average particle size increased when the anatase-TiO2 content decreased.

  19. 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.

  20. Voltage-controlled ferromagnetism and magnetoresistance in LaCoO3/SrTiO3 heterostructures

    Science.gov (United States)

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

    2013-11-01

    A LaCoO3/SrTiO3 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 SrTiO3, leading to an artificial inverse magnetoelectric effect arising from the dependence of ferromagnetism in the LaCoO3 layer on strain. Below the Curie temperature of the LaCoO3 layer, this effect leads to modulation of resistance in LaCoO3 as large as 100%, and magnetoresistance as high as 80%, both of which arise from carrier scattering at ferromagnetic-nonmagnetic interfaces in LaCoO3. 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 LaCoO3 layer. Piezoresponse force microscopy is used to confirm the existence of piezoelectric response in SrTiO3 grown on Si (001). It is also shown that this structure offers the possibility of achieving exclusive-NOR logic functionality within a single device.

  1. Relationship between Crystal Shape, Photoluminescence, and Local Structure in SrTiO3 Synthesized by Microwave-Assisted Hydrothermal Method

    Directory of Open Access Journals (Sweden)

    Luís F. da Silva

    2012-01-01

    Full Text Available This paper describes the effect of using different titanium precursors on the synthesis and physical properties of SrTiO3 powders obtained by microwave-assisted hydrothermal method. X-ray diffraction measurements, X-ray absorption near-edge structure (XANES spectroscopy, field emission scanning electron microscopy (FE-SEM, and high-resolution transmission electron microscopy (HRTEM were carried out to investigate the structural and optical properties of the SrTiO3 spherical and cubelike-shaped particles. The appropriate choice of the titanium precursor allowed the control of morphological and photoluminescence (PL properties of SrTiO3 compound. The PL emission was more intense in SrTiO3 samples composed of spherelike particles. This behavior was attributed to the existence of a lower amount of defects due to the uniformity of the spherical particles.

  2. A nano-grid structure made of perovskite SrTiO3 nanowires for efficient electron transport layers in inverted polymer solar cells.

    Science.gov (United States)

    Kim, Jeong Won; Suh, Yo-han; Lee, Chang-Lyoul; Kim, Yong Seok; Kim, Won Bae

    2015-03-14

    A nano-grid structure of perovskite SrTiO3 NWs is developed for a novel electron transport layer in inverted polymer solar cells. Due to the excellent charge transporting properties of the SrTiO3 nano-grid structure, the device employing this nanostructure showed ∼32% enhanced photovoltaic performance, compared to the solar cell using a TiO2 thin film.

  3. Fabrication and Photocatalytic Property of One-Dimensional SrTiO3/TiO2-xNx Nanostructures

    OpenAIRE

    Huarong Zhang; Miao Guashuai; Ma Xingping; Wang Bei

    2013-01-01

    One-dimensional SrTiO3/TiO2−xNx nanostructures were prepared by the hydrothermal method and investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) measurements. The photocatalytic activities of the prepared samples were evaluated by photodegrading the methylene blue (MB) solution. According to the characterizations, the intermediate product of SrTiO3/titanate...

  4. Role of oxygen vacancies on light emission mechanisms in SrTiO3 induced by high-energy particles

    Science.gov (United States)

    Crespillo, M. L.; Graham, J. T.; Agulló-López, F.; Zhang, Y.; Weber, W. J.

    2017-04-01

    Light emission under MeV hydrogen and oxygen ions in stoichiometric SrTiO3 are identified at temperatures of 100 K, 170 K and room-temperature. MeV ions predominately deposit their energies to electrons in SrTiO3 with energy densities orders of magnitude higher than from UV or x-ray sources but comparable to femtosecond lasers. The ionoluminescence (IL) spectra can be resolved into three main Gaussian bands at 2.0 eV, 2.5 eV and 2.8 eV, whose relative contributions strongly depend on irradiation temperature, electronic energy loss and irradiation fluence. Two main bands, observed at 2.5 eV and 2.8 eV, are intrinsic and associated with electron–hole recombination in the perfect SrTiO3 lattice. The 2.8 eV band is attributed to recombination of free (conduction) electrons with an in-gap level, possibly related to self-trapped holes. Self-trapped excitons (STEs) are considered suitable candidates for the 2.5 eV emission band, which implies a large energy relaxation in comparison to the intrinsic edge transition. The dynamics of electronic excitation, governs a rapid initial rise of the intensity; whereas, accumulated irradiation damage (competing non-radiative recombination channels) accounts for a subsequent intensity decrease. The previously invoked role of isolated oxygen vacancies for the blue luminescence (2.8 eV) does not appear consistent with the data. An increasing well-resolved band at 2.0 eV dominates at 170 K and below. It has been only previously observed in heavily strained and amorphous SrTiO3, and is, here, attributed to transitions from d(t 2g) conduction band levels to d(e g) levels below the gap. In accordance with ab initio theoretical calculations they are associated to trapped electron states in relaxed Ti3+ centers at an oxygen vacancy within distorted TiO6 octahedra. The mechanism of defect evolution monitored during real-time IL experiments is presented. In conclusion, the light emission data confirm that IL is a useful tool to investigate lattice disorder in irradiated SrTiO3.

  5. Energy Spectra, g Factors and Their Pressure-Induced and/or Thermal Shifts of SrTiO3:Cr3+ and SrTiO3:Mn4+ Ⅲ: R-Line Thermal Shifts of SrTiO3:Mn4+

    Institute of Scientific and Technical Information of China (English)

    MA Dong-Ping; ZHANG Ji-Ping

    2001-01-01

    By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d3 electronic configuration,the values of the parameters in the expressions of thermal shift (TS) from EPI for the ground level, R level and R line of SrTiO3:Mn4+ have been evaluated; the R-line TS and various contributions to it have been calculated in the low-temperature region. It is found that all the three terms of R-line TS from EPI relevant to the lattice vibration are red shifts. The Raman term is the largest, the neighbor-level term is the second, and the optical-branch term is very small over the range of T ≤ 80 K. The contribution to R-line TS from thermal expansion has been approximately neglected in this work. The very strong EPI relevant to its lattice vibration for SrTiO3:Mn4+ causes its R-line TS to be an unusually large red-shift. Only by taking into account the strong softening of the low-frequency acoustic modes of the lattice vibration at low temperatures, can we successfully explain the variation of R-line TS of SrTiO3:Mn4+ with temperature.``

  6. Wear and Corrosion Behavior of Zr-Doped DLC on Ti-13Zr-13Nb Biomedical Alloy

    Science.gov (United States)

    Kumar, Prateek; Babu, P. Dilli; Mohan, L.; Anandan, C.; Grips, V. K. William

    2013-01-01

    Zirconium (Zr)-doped DLC was deposited on biomedical titanium alloy Ti-13Nb-13Zr by a combination of plasma-enhanced chemical vapor deposition and magnetron sputtering. The concentration of Zr in the films was varied by changing the parameters of the bi-polar pulsed power supply and the Ar/CH4 gas composition. The coatings were characterized for composition, morphology, nanohardness, corrosion resistance in simulated body fluid (SBF) and tribological properties. X-ray photoelectron spectroscopy (XPS) studies on the samples were used to estimate the concentration of Zr in the films. XPS and micro-Raman studies were used to find the variation of I D/ I G ratio with Zr concentration. These studies show that the disorder in the film increased with increasing Zr concentration as deduced from the I D/ I G ratio. Nanohardness measurements showed no clear dependence of hardness and Young's modulus on Zr concentration. Reciprocating wear studies showed a low coefficient of friction (0.04) at 1 N load and it increased toward 0.4 at higher loads. The wear volume was lower at all loads on the coated samples. The wear mechanism changed from abrasive wear on the substrate to adhesive wear after coating. The corrosion current in SBF was unaffected by the coating and corrosion potential moved toward nobler (more positive) values.

  7. Influence of Experimental Installation on Photocatalytic Activity of Sputtered Nb-Doped TiO2 Thin Film

    Science.gov (United States)

    Hieu, N. M.; Lan, N. T.; Loc, N. B.; Hang, N. T. T.; Tien, N. T.; Thanh, P. V.; Quynh, L. M.; Luong, N. H.; Hoang, N. L. H.

    2017-02-01

    We present an efficient experimental method to investigate the photocatalytic activity of Nb-doped TiO2 (TNO) polycrystalline film deposited on glass substrate by sputtering. The photocatalytic activity of the thin film was evaluated by oxidative photodegradation of methylene blue (MB) solution at wavelength of 292 nm in the ultraviolet (UV) region. Two ways of installing a UV light source to illuminate the sample were demonstrated: (a) with UV light coming from the front of the thin film through the MB solution, and (b) with UV light coming from the back of the thin film through the glass substrate. Compared with installation (a), which is often applied for photocatalytic activity investigation, the influence of the UV light on the dye solution is removed in installation (b), resulting in significantly improved illuminating light intensity. The results show that the photocatalytic efficiency of the thin film with installation (b) was two times higher than that with installation (a). Thus the proposed approach (b) for installing the UV light source is more promising for investigation of photocatalytic properties.

  8. Homogeneous interface-type resistance switching in Au/La0.67Ca0.33MnO3/SrTiO3/F(:)SnO2heterojunction memories

    Institute of Scientific and Technical Information of China (English)

    Zhang Ting; Ding Ling-Hong; Zhang Wei-Feng

    2012-01-01

    La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer.The current-voltage characteristics of the heterojunctions exhibit an asymmetric and resistance switching behaviour.A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy.The spatial homogeneity of the charge carrier distribution leads to fieldinduced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect.The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 × 104% by simulating the AC electric field.This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.

  9. High power Nb-doped LiFePO4 Li-ion battery cathodes; pilot-scale synthesis and electrochemical properties

    Science.gov (United States)

    Johnson, Ian D.; Blagovidova, Ekaterina; Dingwall, Paul A.; Brett, Dan J. L.; Shearing, Paul R.; Darr, Jawwad A.

    2016-09-01

    High power, phase-pure Nb-doped LiFePO4 (LFP) nanoparticles are synthesised using a pilot-scale continuous hydrothermal flow synthesis process (production rate of 6 kg per day) in the range 0.01-2.00 at% Nb with respect to total transition metal content. EDS analysis suggests that Nb is homogeneously distributed throughout the structure. The addition of fructose as a reagent in the hydrothermal flow process, followed by a post synthesis heat-treatment, affords a continuous graphitic carbon coating on the particle surfaces. Electrochemical testing reveals that cycling performance improves with increasing dopant concentration, up to a maximum of 1.0 at% Nb, for which point a specific capacity of 110 mAh g-1 is obtained at 10 C (6 min for the charge or discharge). This is an excellent result for a high power cathode LFP based material, particularly when considering the synthesis was performed on a large pilot-scale apparatus.

  10. Attractive electron-electron interactions at the LaAlO3/SrTiO3 Interface

    DEFF Research Database (Denmark)

    Prawiroatmodjo, Guenevere E D K

    The conducting interface between the two insulating oxides LaAlO3 and SrTiO3 (LAO/STO) exhibits many intriguing properties such as high mobility, a gate-tunable superconducting phase, ferroelectricity and ferromagnetism. In this thesis, devices are fabricated at the LAO/STO interface using novel...... hard-mask patterning techniques with micrometer precision. The superconducting phase diagram is explored in terms of critical magnetic field Bc, temperature Tc and current Ic, and studied for varying carrier densities. From a finite shift between the superconducting Tc and Ic domes, evidence is found...

  11. Phonon Calculations in Cubic and Tetragonal Phases of SrTiO3: a Comparative LCAO and Plane Wave Study

    OpenAIRE

    Evarestov, Robert A.; Blokhin, Evgeny; Gryaznov, Denis; Kotomin, Eugene A.; Maier, Joachim

    2010-01-01

    The atomic, electronic structure and phonon frequencies have been calculated in a cubic and low-temperature tetragonal SrTiO3 phases at the ab initio level. We demonstrate that the use of hybrid exchange-correlation PBE0 functional gives the best agreement with experimental data. The results for the standard PBE and hybrid PBE0 are compared for the two types of basis sets: a linear combination of atomic orbitals (LCAO, CRYSTAL09 computer code) and plane waves (PW, VASP 5.2 code). Relation bet...

  12. Polarity-induced oxygen vacancies at LaAlO3|SrTiO3 interfaces

    OpenAIRE

    Zhong, Zhicheng; Xu, P. X.; Kelly, Paul J.

    2010-01-01

    Using first-principles density-functional-theory calculations, we find a strong position and thickness dependence of the formation energy of oxygen vacancies in LaAlO3 vertical bar SrTiO3 (LAO vertical bar STO) multilayers and interpret this with an analytical capacitor model. Oxygen vacancies are preferentially formed at p-type SrO vertical bar AlO2 rather than at n-type LaO vertical bar TiO2 interfaces; the excess electrons introduced by the oxygen vacancies reduce their energy by moving to...

  13. Study of electronic structure and magnetism at the relaxed SrTiO3/LaAlO3 interface

    Science.gov (United States)

    Ghosh, Soham; Manousakis, Efstratios

    2013-03-01

    The SrTiO3/LaAlO3 interface has been found experimentally to be metallic and magnetic, with bandstructure calculations linking both phenomena to polar catastrophe and surface oxygen vacancies. In this work, we use LDA+U to study the properties of this interface, allowing the ionic structure to be fully relaxed, and investigate the 2-dimensional nature of the electron gas formed at the junction. We present an effort to understand the role of electron-electron correlation on the interfacial collective phenomena, by constructing extended Hubbard-like models based on bandstructure calculation.

  14. Morphology and structural studies of WO3 films deposited on SrTiO3 by pulsed laser deposition

    Science.gov (United States)

    Kalhori, Hossein; Porter, Stephen B.; Esmaeily, Amir Sajjad; Coey, Michael; Ranjbar, Mehdi; Salamati, Hadi

    2016-12-01

    WO3 films have been grown by pulsed laser deposition on SrTiO3 (001) substrates. The effects of substrate temperature, oxygen partial pressure and energy fluence of the laser beam on the physical properties of the films were studied. Reflection high-energy electron diffraction (RHEED) patterns during and after growth were used to determine the surface structure and morphology. The chemical composition and crystalline phases were obtained by XPS and XRD respectively. AFM results showed that the roughness and skewness of the films depend on the substrate temperature during deposition. Optimal conditions were determined for the growth of the highly oriented films.

  15. Thermodynamic and kinetic properties of hydrogen defect pairs in SrTiO3 from density functional theory

    DEFF Research Database (Denmark)

    Bork, Nicolai Christian; Bonanos, Nikolaos; Rossmeisl, Jan

    2011-01-01

    A density functional theory investigation of the thermodynamic and kinetic properties of hydrogen–hydrogen defect interactions in the cubic SrTiO3 perovskite is presented. We find a net attraction between two hydrogen atoms with an optimal separation of ∼2.3 Å. The energy gain is ca. 0.33 e......V compared to two non-interacting H defects. The main cause of the net attractive potential is elastic defect interactions through lattice deformation. Two possible diffusion paths for the hydrogen defect pair are investigated and are both determined to be faster than the corresponding diffusion path...

  16. Two-dimensional superconductivity at the (111)LaAlO 3/SrTiO 3 interface

    Science.gov (United States)

    Monteiro, A. M. R. V. L.; Groenendijk, D. J.; Groen, I.; de Bruijckere, J.; Gaudenzi, R.; van der Zant, H. S. J.; Caviglia, A. D.

    2017-07-01

    We report on the discovery and transport study of the superconducting ground state present at the (111)LaAlO3/SrTiO3 (LAO/STO) interface. The superconducting transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and its two-dimensional nature is further corroborated by the anisotropy of the critical magnetic field, as calculated by Tinkham. The estimated superconducting layer thickness and coherence length are 10 and 60 nm , respectively. The results of this work provide insight to clarify the microscopic details of superconductivity in LAO/STO interfaces, in particular in what concerns the link with orbital symmetry.

  17. Oxygen vacancy clustering and electron localization in oxygen-deficient SrTiO(3): LDA + U study.

    Science.gov (United States)

    Cuong, Do Duc; Lee, Bora; Choi, Kyeong Mi; Ahn, Hyo-Shin; Han, Seungwu; Lee, Jaichan

    2007-03-16

    We find, using a local density approximation +Hubbard U method, that oxygen vacancies tend to cluster in a linear way in SrTiO(3), a prototypical perovskite oxide, accompanied by strong electron localization at the 3d state of the nearby Ti transition metal ion. The vacancy clustering and the associated electron localization lead to a profound impact on materials properties, e.g., the reduction in free-carrier densities, the appearance of characteristic optical spectra, and the decrease in vacancy mobility. The high stability against the vacancy migration also suggests the physical reality of the vacancy cluster.

  18. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics.

    Science.gov (United States)

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-02-06

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I-V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I-V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I-V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I-V behavior of (Nb + In) co-doped TiO2 ceramics.

  19. Plasmons at the LaAlO3/SrTiO3 interface and in the graphene-LaAlO3/SrTiO3 double layer

    Science.gov (United States)

    Faridi, A.; Asgari, Reza

    2017-04-01

    We study plasmon modes of the two-dimensional electron gas residing at the interface of band insulators LaAlO3 and SrTiO3 (LAO/STO) and the plasmon excitations of graphene-LAO/STO double layer as well. Considering the electron-electron interaction within random phase approximation, we calculate the plasmon dispersions of both systems numerically and in the long-wavelength limit analytical expressions for collective modes are found. One optical mode and two (three) acoustic modes are predicted for the LAO/STO (graphene-LAO/STO) system where only the uppermost acoustic mode of both systems can emerge above the electron-hole continuum depending on the characteristics of each system. In the case of LAO/STO interface, thanks to the spatial separation between t2 g orbitals, the upper acoustic mode might be undamped at the long-wavelength limit depending on the exact value of the dielectric constant of SrTiO3. Same as other double layer systems, the interlayer distance for the graphene-LAO/STO system plays a crucial role in damping the upper acoustic mode. Faster damping of all plasmon modes of the present double layer system in comparison with the ones with conventional two-dimensional electron gas instead of t2 g electron gas is also found due to heavier effective masses of the gas and also stronger interlayer Coulomb interaction.

  20. Enhanced photoelectrical performance of dye-sensitized solar cells with double-layer TiO2 on perovskite SrTiO3 substrate

    Science.gov (United States)

    Liu, Qiuhong; Sun, Qiong; Zhang, Min; Li, Yang; Zhao, Mei; Dong, Lifeng

    2016-04-01

    In this research, perovskite SrTiO3 particles are synthesized by a hydrothermal method, and TiO2 with a double-layer structure is grown on the SrTiO3 surface by a hydrolysis-condensation process. Structural characterizations reveal that TiO2 comprises of two phases: anatase film at the bottom and single-crystal rutile nanorods grown along the [110] direction on top. The TiO2-SrTiO3 composite film is investigated as photoanode material for dye-sensitized solar cells. In comparison with pure TiO2 and SrTiO3, the composite photoanode shows a much better performance in photoelectric conversion efficiency (1.35 %), which is about 2 and 100 times as efficient as pure TiO2 and SrTiO3, respectively. This indicates that the composite structure can facilitate charge carrier transfer and reduce electron-hole recombination to enhance photoelectrical properties of TiO2-based photoanode materials.

  1. 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

    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...... to the enhanced electronic conductivity and despite the reduced ionic conductivity....

  2. Thickness Effect of Nb-Doped TiO2 Transparent Conductive Oxide Grown on Glass Substrates Fabricated by RF Sputtering

    Science.gov (United States)

    Tseng, Zong-Liang; Chen, Lung-Chien; Tang, Jian-Fu; Shih, Meng-Fu; Chu, Sheng-Yuan

    2017-03-01

    Transparent conducting Nb-doped titanium oxide (NTO) films were deposited on a non-alkali glass substrate using an RF magnetron sputtering method with post-annealing. Structural, electrical and optical properties of the NTO films were found to be strongly dependent on film thickness. A resistivity of 4.2 × 10-3 Ω cm and an average visible transmittance of ˜70% were obtained at the film thickness of 360 nm, indicating that the polycrystalline NTO fabricated by the sputtering method has sufficient potential as a transparent conducting oxide (TCO) candidate for practical applications.

  3. Influence of Cr Doping on the Critical Behavior of Amorphous Alloy Ribbons Fe78–xCrxSi4Nb5B12Cu1

    DEFF Research Database (Denmark)

    Phan, The-Long; Thanh, P. Q.; Chau, N.

    2014-01-01

    Though many previous works focused on studying Cr-doped Fe–Si–Nb–B–Cu amorphous alloys, magnetic-interaction mechanismsin these materials have not been carefully investigated yet. Dealing with these issues, we have prepared the amorphous alloy ribbonsFe78−xCrx Si4Nb5B12Cu1 with x = 1, 3, and 6...... = 0.367–0.376 and γ = 1.315–1.338. These values are close to those expected forthe 3-D Heisenberg model with β = 0.365 and γ = 1.336, proving the existence of short-range FM order in the amorphous alloyribbons....

  4. Optical Waveguide Property of Nd-doped Laser Materials Ndx Y1-x A13(BO3) 4 and Nd∶MgO∶LiNbO3

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Lanthanide has attracted much attention in the field of optical communications in recent years. Some property analyses on optical waveguide of Nd-doped crystal NdxY1-xA13(BO3)4 and Nd∶MgO∶LiNbO3 are made in this paper, followed by introduction of the methods of experimentation and theoretical calculation for the planar optical waveguides. The refractive index profiles of the optical waveguides are analyzed. The above work offers useful information for study on new type materials for optical communications.

  5. Thickness Effect of Nb-Doped TiO2 Transparent Conductive Oxide Grown on Glass Substrates Fabricated by RF Sputtering

    Science.gov (United States)

    Tseng, Zong-Liang; Chen, Lung-Chien; Tang, Jian-Fu; Shih, Meng-Fu; Chu, Sheng-Yuan

    2016-12-01

    Transparent conducting Nb-doped titanium oxide (NTO) films were deposited on a non-alkali glass substrate using an RF magnetron sputtering method with post-annealing. Structural, electrical and optical properties of the NTO films were found to be strongly dependent on film thickness. A resistivity of 4.2 × 10-3 Ω cm and an average visible transmittance of ˜70% were obtained at the film thickness of 360 nm, indicating that the polycrystalline NTO fabricated by the sputtering method has sufficient potential as a transparent conducting oxide (TCO) candidate for practical applications.

  6. Sandwich-Type NbS2@S@I-Doped Graphene for High-Sulfur-Loaded, Ultrahigh-Rate, and Long-Life Lithium-Sulfur Batteries.

    Science.gov (United States)

    Xiao, Zhubing; Yang, Zhi; Zhang, Linjie; Pan, Hui; Wang, Ruihu

    2017-08-22

    Lithium-sulfur batteries practically suffer from short cycling life, low sulfur utilization, and safety concerns, particularly at ultrahigh rates and high sulfur loading. To address these problems, we have designed and synthesized a ternary NbS2@S@IG composite consisting of sandwich-type NbS2@S enveloped by iodine-doped graphene (IG). The sandwich-type structure provides an interconnected conductive network and plane-to-point intimate contact between layered NbS2 (or IG) and sulfur particles, enabling sulfur species to be efficiently entrapped and utilized at ultrahigh rates, while the structural integrity is well maintained. NbS2@S@IG exhibits prominent high-power charge/discharge performances. Reversible capacities of 195, 107, and 74 mA h g(-1) (1.05 mg cm(-2)) have been achieved after 2000 cycles at ultrahigh rates of 20, 30, and 40 C, respectively, and the corresponding average decay rates per cycle are 0.022%, 0.031% and 0.033%, respectively. When the area sulfur loading is increased to 3.25 mg cm(-2), the electrode still maintains a high discharge capacity of 405 mAh g(-1) after 600 cycles at 1 C. Three half-cells in series assembled with NbS2@S@IG can drive 60 indicators of LED modules after only 18 s of charging. The instantaneous current and power of the device reach 196.9 A g(-1) and 1369.7 W g(-1), respectively.

  7. Epitaxial strain and its relaxation at the LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Liu, Guozhen; Lei, Qingyu; Wolak, Matthäus A.; Li, Qun; Chen, Long-Qing; Winkler, Christopher; Sloppy, Jennifer; Taheri, Mitra L.; Xi, Xiaoxing

    2016-08-01

    A series of LaAlO3 thin films with different thicknesses were deposited by pulsed laser deposition at temperatures from 720 °C to 800 °C. The results from grazing incidence x-ray diffraction and reciprocal space mapping indicate that a thin layer of LaAlO3 adjacent to the SrTiO3 substrate remains almost coherently strained to the substrate, while the top layer starts to relax quickly above a certain critical thickness, followed by a gradual relaxation at larger film thickness when they are grown at lower temperatures. The atomic force microscopy results show that the fast relaxation is accompanied by the formation of cracks on the film surface. This can be ascribed to the larger energy release rate when compared with the resistance of LaAlO3 to cracking, according to calculations from the Griffith fracture theory. For films grown at 720 °C, a drop in sheet resistance by two orders of magnitude is observed when the top layer starts to relax, indicating a relationship between the strain and the conductivity of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. The strain engineered by growth temperature provides a useful tool for the manipulation of the electronic properties of oxide heterointerfaces.

  8. Electronic and magnetic properties of SrTiO(3)/LaAlO(3) interfaces from first principles.

    Science.gov (United States)

    Chen, Hanghui; Kolpak, Alexie M; Ismail-Beigi, Sohrab

    2010-07-20

    A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO(3) and SrTiO(3). These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO(3)/LaAlO(3) interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies.

  9. Epitaxial Fe3Pt/FePt nanocomposites on MgO and SrTiO3

    Science.gov (United States)

    Casoli, F.; Lupo, P.; Nasi, L.; Cabassi, R.; Fabbrici, S.; Bolzoni, F.; Ranzieri, P.; Albertini, F.

    2015-02-01

    We have exploited the pseudomorphic growth of the magnetically soft Fe3Pt phase on top of L10-FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO3(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchange-coupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreases down to 21% of the hard layer value for Fe3Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO3; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%.

  10. Aharanov-Bohm quantum interference in LaAlO3/SrTiO3 Hall bar structures

    Science.gov (United States)

    Irvin, Patrick; Lu, Shicheng; Annadi, Anil; Cheng, Guanglei; Tomczyk, Michelle; Huang, Mengchen; Levy, Jeremy; Lee, Hyungwoo; Eom, Chang-Beom

    Aharanov-Bohm (AB) interference can arise in transport experiments when magnetic flux threads through two or more transport channels. The existence of this behavior requires long-range ballistic transport and is typically observed only in exceptionally clean materials. We observe AB interference in wide (w ~ 100 nm) channels created at the LaAlO3/SrTiO3 interface using conductive AFM lithography. Interference occurs above a critical field B ~ 4 T and increases in magnitude with increasing magnetic field. The period of oscillation implies a ballistic length that greatly exceeds the micron-scale length of the channel, consistent with Fabry-Perot interference in 1D channels. The conditions under which AB oscillations are observed will be discussed in the context of the electron pairing mechanism in LaAlO3/SrTiO3. We gratefully acknowledge financial support from AFOSR (FA9550-10-1-0524 (JL), FA9550-12-1-0268 (JL), and FA9550-12-1-0342 (CBE)) and NSF (DMR-1124131 (JL), DMR-1104191 (JL), and DMR-1234096 (CBE)).

  11. On the origin of metallic conductivity at the interface of LaAlO3/SrTiO3

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Christensen, Dennis; Trier, Felix

    2012-01-01

    To determine the origin of the quasi-two-dimensional electron gas formed at the interface between the two complex oxides of LaAlO3 (LAO) and SrTiO3 (STO), various amorphous films of LAO, La2O3, Al2O3, and La7/8Sr1/8MnO3 (LSMO), were deposited on TiO2-terminated (0 0 1) STO substrates by pulsed...... laser deposition at room temperature. Metallic interfaces are observed when the over-layers are amorphous LAO, La2O3, or Al2O3, while insulating interfaces are observed when the over-layer is LSMO. The interfacial conductivity of these SrTiO3-based hetero-structures shows strong dependence on both film...... thickness and oxygen pressure during film growth. The possible origin for the occurrence of metallic interfaces in these complex oxide hetero-structures due to redox reactions at the STO substrate surface is discussed. A thermodynamic criterion for designing either metallic or insulating interfaces between...

  12. Anisotropic electrical resistance in mesoscopic LaAlO3/SrTiO3 devices with individual domain walls.

    Science.gov (United States)

    Goble, Nicholas J; Akrobetu, Richard; Zaid, Hicham; Sucharitakul, Sukrit; Berger, Marie-Hélène; Sehirlioglu, Alp; Gao, Xuan P A

    2017-03-15

    The crystal structure of bulk SrTiO3(STO) transitions from cubic to tetragonal at around 105 K. Recent local scanning probe measurements of LaAlO3/SrTiO3 (LAO/STO) interfaces indicated the existence of spatially inhomogeneous electrical current paths and electrostatic potential associated with the structural domain formation in the tetragonal phase of STO. Here we report a study of temperature dependent electronic transport in combination with the polarized light microscopy of structural domains in mesoscopic LAO/STO devices. By reducing the size of the conductive interface to be comparable to that of a single tetragonal domain of STO, the anisotropy of interfacial electron conduction in relationship to the domain wall and its direction was characterized between T = 10-300 K. It was found that the four-point resistance measured with current parallel to the domain wall is larger than the resistance measured perpendicular to the domain wall. This observation is qualitatively consistent with the current diverting effect from a more conductive domain wall within the sample. Among all the samples studied, the maximum resistance ratio found is at least 10 and could be as large as 10(5) at T = 10 K. This electronic anisotropy may have implications on other oxide hetero-interfaces and the further understanding of electronic/magnetic phenomena found in LAO/STO.

  13. Anisotropic electrical resistance in mesoscopic LaAlO3/SrTiO3 devices with individual domain walls

    Science.gov (United States)

    Goble, Nicholas J.; Akrobetu, Richard; Zaid, Hicham; Sucharitakul, Sukrit; Berger, Marie-Hélène; Sehirlioglu, Alp; Gao, Xuan P. A.

    2017-01-01

    The crystal structure of bulk SrTiO3(STO) transitions from cubic to tetragonal at around 105 K. Recent local scanning probe measurements of LaAlO3/SrTiO3 (LAO/STO) interfaces indicated the existence of spatially inhomogeneous electrical current paths and electrostatic potential associated with the structural domain formation in the tetragonal phase of STO. Here we report a study of temperature dependent electronic transport in combination with the polarized light microscopy of structural domains in mesoscopic LAO/STO devices. By reducing the size of the conductive interface to be comparable to that of a single tetragonal domain of STO, the anisotropy of interfacial electron conduction in relationship to the domain wall and its direction was characterized between T = 10–300 K. It was found that the four-point resistance measured with current parallel to the domain wall is larger than the resistance measured perpendicular to the domain wall. This observation is qualitatively consistent with the current diverting effect from a more conductive domain wall within the sample. Among all the samples studied, the maximum resistance ratio found is at least 10 and could be as large as 105 at T = 10 K. This electronic anisotropy may have implications on other oxide hetero-interfaces and the further understanding of electronic/magnetic phenomena found in LAO/STO. PMID:28295058

  14. Structural Behaviour of Solid Solutions in the NdAlO3-SrTiO3 System

    Science.gov (United States)

    Ohon, Natalia; Stepchuk, Roman; Blazhivskyi, Kostiantyn; Vasylechko, Leonid

    2017-02-01

    Single-phase mixed aluminates-titanates Nd1- x Sr x Al1- x Ti x O3 ( x = 0.3 ÷ 0.9) were prepared from stoichiometric amounts of constituent oxides Nd2O3, Al2O3, TiO2 and strontium carbonate SrCO3 by solid-state reaction technique in air at 1773 K. Crystal structure parameters of Nd1- x Sr x Al1- x Ti x O3 were refined by full-profile Rietveld refinement in space groups R overline{3} c ( x = 0.3, 0.5, 0.7 and 0.8) and Pm overline{3} m ( x = 0.9). Comparison of the obtained structural parameters with the literature data for the end members of the system NdAlO3 and SrTiO3 revealed formation of two kinds of solid solutions Nd1-xSrxAl1-xTixO3 with the cubic and rhombohedral perovskite structure. Morphotropic rhombohedral-to-cubic phase transition in Nd1-xSrxAl1-xTixO3 series occurs at x = 0.84. Based on the results obtained as well as the literature data for the parent compounds, the tentative phase diagram of the NdAlO3-SrTiO3 pseudo-binary system have been constructed.

  15. Role of interface structure and chemistry in resistive switching of NiO nanocrystals on SrTiO3

    Directory of Open Access Journals (Sweden)

    Xuan Cheng

    2014-03-01

    Full Text Available Nickel oxide (NiO nanocrystals epitaxially grown on (001 strontium titanate (SrTiO3 single crystal substrates were characterized to investigate interface morphology and chemistry. Aberration corrected high angle annular dark field scanning transmission electron microscopy reveals the interface between the NiO nanocrystals and the underlying SrTiO3 substrate to be rough, irregular, and have a lower average atomic number than the substrate or the nanocrystal. Energy dispersive x-ray spectroscopy and electron energy loss spectroscopy confirm both chemical disorder and a shift of the energy of the Ti L2,3 peaks. Analysis of the O K edge profiles in conjunction with this shift, implies the presence of oxygen vacancies at the interface. This sheds light into the origin of the previously postulated minority carriers’ model to explain resistive switching in NiO [J. Sullaphen, K. Bogle, X. Cheng, J. M. Gregg, and N. Valanoor, Appl. Phys. Lett. 100, 203115 (2012].

  16. Effects of Nb doping on the microstructure, ferroelectric and piezoelectric properties of 0.7BiFeO$_3$–0.3BaTiO$_3$ lead-free ceramics

    Indian Academy of Sciences (India)

    XIAOLAN WU; LINGLING LUO; NA JIANG; XIAOCHUN WU; QIAOJI ZHENG

    2016-06-01

    Donor-doped lead-free Bi$_{0.7}$Ba$_{0.3}$(Fe$_{0.7}$Ti$_{0.3}$)$_{1−x}$Nb$_{0.66x}$O$_{3}$ + 1 mol% MnO$_2$ ceramics were prepared by a conventional oxide-mixed method and the effects of Nb-doping on microstructure, piezoelectric and ferroelectricproperties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure with rhombohedral symmetry. The grain growth of the ceramics is inhibited after the addition of Nb doping. High electricinsulation ($R = 10^9–10^{10}$ $\\Omega$·cm) and the poor piezoelectric performance and weak ferroelectricity are observed after the addition of Nb$_2$O$_5$ in the ceramics. Different from the donor effect of Pb-based perovskite ceramics, the introduction of Nb into 0.7BiFeO$_3$–0.3BaTiO$_3$ degrades the piezoelectricity and ferroelectricity of the ceramics. The Bi$_{0.7}$Ba$_{0.3}$(Fe$_{0.7}$Ti$_{0.3}$)$_{1−x}$Nb$_{0.66}$xO$_3$ + 1 mol% MnO2 ceramic with $x = 0$ exhibits the optimum piezoelectric properties with $d_{33} = 133$ pN C$^{−1}$ and $k_p = 0.29$ and high Curie temperature ($T_C = 603^{\\circ}$C).

  17. Observation of a dodecagonal oxide quasicrystal and its complex approximant in the SrTiO3-Pt(1 1 1) system

    Science.gov (United States)

    Schenk, Sebastian; Förster, Stefan; Meinel, Klaus; Hammer, René; Leibundgut, Bettina; Paleschke, Maximilian; Pantzer, Jonas; Dresler, Christoph; Schumann, Florian O.; Widdra, Wolf

    2017-04-01

    We report on the formation of a SrTiO3-derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(1 1 1). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO3-derived OQC exhibits strong similarities to the BaTiO3-derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO3-derived OQC is 1.8% smaller. Coexisting with the OQC a large scale approximant structure with a monoclinic unit cell is identified. It demonstrates the extraordinary level of complexity that oxide approximant structures can reach.

  18. Controlling the conductivity of amorphous LaAlO3/SrTiO3 interfaces by in-situ application of an electric field during fabrication

    DEFF Research Database (Denmark)

    Trier, Felix; Amoruso, S.; Christensen, Dennis Valbjørn

    2013-01-01

    Amorphous-LaAlO3/SrTiO3 interfaces present metallic conductivity similar to those found in their all-crystalline counterparts. Here, the conductivity of amorphous-LaAlO3/SrTiO3 interfaces is modified by an external electric field applied in-situ with a biased truncated cone electrode (−10 V ≤ Vbias...... ≤ 20 V) during film growth. By modulating the charge balance of the arriving plasma species, interfacial conduction of the amorphous-LaAlO3/SrTiO3 heterostructures shifts from metallic to insulating via a semiconducting-like characteristic transport mode. This remarkable behavior is explained...

  19. 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.

  20. Full compensation of oxygen vacancies in EuTiO3 (001) epitaxial thin film stabilized by a SrTiO3 surface protection layer

    Science.gov (United States)

    Shimamoto, K.; Hatabayashi, K.; Hirose, Y.; Nakao, S.; Fukumura, T.; Hasegawa, T.

    2013-01-01

    We fabricated highly insulating EuTiO3 (001) epitaxial thin films capped with SrTiO3 protection layers on SrTiO3 (001) substrates by combining pulsed laser deposition and post-annealing processes. The epitaxial SrTiO3 protection layer played a significant role in compensation of oxygen vacancies in the EuTiO3 thin films by preventing excess oxidation of the films and by "locking" the EuTiO3 perovskite structure in an epitaxial manner from the top during the air-annealing process. The obtained EuTiO3 thin films demonstrated an antiferromagnetic transition at 5.4 K, quantum paraelectricity down to ˜25 K, and a magnetoelectric coupling comparable to that of bulk EuTiO3.

  1. Electric field control of magnetic anisotropy in a Co/Pt bilayer deposited on a high-κ SrTiO3

    Science.gov (United States)

    Nakazawa, S.; Obinata, A.; Chiba, D.; Ueno, K.

    2017-02-01

    The perpendicular magnetic anisotropy (PMA) of a Co (0.5 nm)/Pt (2.4 nm) bilayer film was electrostatically tuned using a high-κ dielectric, SrTiO3, with a back-gating configuration. The Co film was directly deposited onto a SrTiO3 (001) substrate and capped by a Pt layer. The coercivity was enhanced (reduced) by applying a positive (negative) gate bias. The efficiency of the PMA energy modulation by the electric field was determined to be 1300-23 100 fJ/V m, which is 1-3 orders of magnitude higher than the efficiencies obtained in previous studies. The superior efficiency of this system is most likely attributable to the large dielectric constant of the SrTiO3 gate insulator and could be evidence that the PMA energy modulation is induced by charge accumulation.

  2. Predictive Control over Charge Density in the Two-Dimensional Electron Gas at the Polar-Nonpolar NdTiO3/SrTiO3 Interface

    Science.gov (United States)

    Xu, Peng; Ayino, Yilikal; Cheng, Christopher; Pribiag, Vlad S.; Comes, Ryan B.; Sushko, Peter V.; Chambers, Scott A.; Jalan, Bharat

    2016-09-01

    Through systematic control of the Nd concentration, we show that the carrier density of the two-dimensional electron gas (2DEG) in SrTiO3/NdTiO3/SrTiO3(001 ) can be modulated over a wide range. We also demonstrate that the NdTiO3 in heterojunctions without a SrTiO3 cap is degraded by oxygen absorption from air, resulting in the immobilization of donor electrons that could otherwise contribute to the 2DEG. This system is, thus, an ideal model to understand and control the insulator-to-metal transition in a 2DEG based on both environmental conditions and film-growth processing parameters.

  3. Effect of the out-of-plane stress on the properties of epitaxial SrTiO3 films with nano-pillar array on Si-substrate

    Science.gov (United States)

    Bai, Gang; Xie, Qiyun; Liu, Zhiguo; Wu, Dongmei

    2015-08-01

    A nonlinear thermodynamic formalism has been proposed to calculate the physical properties of the epitaxial SrTiO3 films containing vertical nano-pillar array on Si-substrate. The out-of-plane stress induced by the mismatch between film and nano-pillars provides an effective way to tune the physical properties of ferroelectric SrTiO3 films. Tensile out-of-plane stress raises the phase transition temperature and increases the out-of-plane polarization, but decreases the out-of-plane dielectric constant below Curie temperature, pyroelectric coefficient, and piezoelectric coefficient. These results showed that by properly controlling the out-of-plane stress, the out-of-plane stress induced paraelectric-ferroelectric phase transformation will appear near room temperature. Excellent dielectric, pyroelectric, piezoelectric properties of these SrTiO3 films similar to PZT and other lead-based ferroelectrics can be expected.

  4. Dielectric, Ferroelectric, and Piezoelectric Properties of Mn-Doped K0.5Na0.5NbO3 Lead-Free Ceramics

    Science.gov (United States)

    Lopez-Juarez, Rigoberto; Gomez-Vidales, Virginia; Cruz, M. P.; Villafuerte-Castrejon, M. E.

    2015-08-01

    In this work, study of manganese-doped potassium-sodium niobate ceramics was performed. It was found that, with increasing Mn2+ content from 1 mol.% to 1.5 mol.%, the Q m changed from 60 to near 500 with no appreciable detriment in piezoelectric properties. These properties first increased with 0.5 mol.%, and remained almost constant with 1 mol.% of manganese. Maximum values for d 33, d 31, and k p were 120 pC N-1, 33 pC N-1, and 36%, respectively. Thus, manganese-doped K0.5Na0.5NbO3 ceramics represent an option for high-power applications.

  5. 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.

  6. Magneto-transport properties of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction

    Indian Academy of Sciences (India)

    P Raychaudhuri; C Mitra; K Dorr; K H Muller; G Kobernik; R Pinto

    2002-05-01

    Hole-doped rare-earth manganite La0.7Ca0.3MnO3 and the electron-doped manganite La0.7Ce0.3MnO3 both show a metal–insulator transition around 250 K associated with a ferromagnetic transition and colossal magnetoresistance. In an earlier publication we have reported the rectifying characteristic of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction at room temperature, showing that it is possible to fabricate a diode out of the polaronic insulator regime of doped manganites. Here we report the magneto-transport properties of such a tunnel junction above and below the metal–insulator transition. We show, from the large positive magnetoresistance of the tunnel junction at low temperature, that La0.7Ce0.3MnO3 could be a minority spin carrier ferromagnet. The implication of this observation is discussed.

  7. Energy Spectra,g Factors and Their Pressure-Induced and/or Thermal Shifts of SrTiO3:Cr3+ and SrTiO3:Mn4+ IV:R-Line Thermal Shifts of SrTiO3:Cr3+

    Institute of Scientific and Technical Information of China (English)

    MA Dong-Ping; ZHANG Ji-Ping

    2001-01-01

    The local impurity-vibration modes (especially,the Iow-frequency one) of SrTiO3 :Cr3+ cause a very large R-line blue-shift;while the Raman term,neighbor-level term and optical-branch term relevant to the lattice vibration cause smallred shifts.The algebraic sum of them gives rise to the observed unusual and large R-line thermal shift (blue-shift) of SrTiOa:Cr3+.By taking into account all the irreducible representations and their components in the electron-phonon interaction (BPI) as well as all the levels and the admixtures of basic wavefunctions within d3 electronic configuration,the values of the parameters in the expressions of thermal shift (TS) from EPI for the ground level,R level and R line of SrTiO3:Cr3+ have been evaluated;the R-line TS and various contributions to it have been calculated in two temperature ranges (30 K ≤ T ≤ 80 K and 130 K ≤ T ≤ 300 K).The contribution to R-line TS from thermal expansion has been approximately neglected in this work.Furthermore,the improvement on simplified approximation of adopting a single low-frequency impurity-mode and neglecting its hardening in Iow-temperature region has been made.``

  8. Origin of the two-dimensional electron gas at LaAlO3/SrTiO3 interfaces: The role of oxygen vacancies and electronic reconstruction

    OpenAIRE

    COEY, JOHN; Venkatesan, Munuswamy

    2013-01-01

    PUBLISHED The relative importance of atomic defects and electron transfer in explaining conductivity at the crystalline LaAlO3=SrTiO3 interface has been a topic of debate. Metallic interfaces with similar electronic properties produced by amorphous oxide overlayers on SrTiO3 [Y. Chen et al., Nano Lett. 11, 3774 (2011); S.W. Lee et al., Nano Lett. 12, 4775 (2012)] have called in question the original polarization catastrophe model [N. Nakagawa et al., Nature Mater. 5, 204 (2006)]. We resolv...

  9. Grain boundary defect compensation in Ti-doped BaFe0.5Nb0.5O3 ceramics

    Science.gov (United States)

    Sun, Xiaojun; Deng, Jianming; Liu, Saisai; Yan, Tianxiang; Peng, Biaolin; Jia, Wenhao; Mei, Zaoming; Su, Hongbo; Fang, Liang; Liu, Laijun

    2016-09-01

    Giant dielectric ceramics Ba(Nb0.5Fe0.5- x Ti x )O3 (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 ( ɛ') 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 ( ɛ') 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 Ti4+-doped Ba(Nb0.5Fe0.5)O3 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(Nb0.5Fe0.5)O3 ceramics.

  10. Reversible ion exchange and structural stability of garnet-type Nb-doped Li7La3Zr2O12 in water for applications in lithium batteries

    Science.gov (United States)

    Liu, Cai; Rui, Kun; Shen, Chen; Badding, Michael E.; Zhang, Gaoxiao; Wen, Zhaoyin

    2015-05-01

    H+/Li+ ion exchange and structural stability of the high ionic conductivity Nb-doped Zr-garnet Li6.75La3Nb0.25Zr1.75O12 (LLNZO) are investigated in this study. Relationships between ion exchange and Li-population per unit cell, which are necessary to establish the practical framework of garnet electrolytes, are deduced for garnet oxides within ion-exchange process. H+/Li+ ion exchange of cubic LLNZO powder is performed continuously in distilled water and products with various exchange levels are obtained via this simple method. FTIR spectra show the evolution of H-O bonding through the ion-exchange process. A maximum of 74.8% exchange of Li+ by H+ was found, consistent with a preferential replacement of octahedrally coordinated Li. The cubic garnet phase is maintained throughout all levels of proton exchange observed. The formation of garnet-type solid solution of Li6.75-xHxLa3Nb0.25Zr1.75O12 is indicated by well-resolved lattice fringes as well as the linear evolution of crystal lattice parameters with the ion exchange level. The reverse ion exchange of H+ by Li+ is successfully achieved in Li+ containing aqueous solutions, demonstrating its high structural stability and good compatibility for promising applications in lithium batteries.

  11. Optical spectra and local structure of Eu3+ ions doped in Nb2O5-La2O3-B2O3-BaO glasses

    Institute of Scientific and Technical Information of China (English)

    Haiping Xia; Jianli Zhang; Jinhao Wang; Yuepin Zhang

    2006-01-01

    @@ The xNb2O5-(15-x)La2O3-40B2O3-45BaO (x = 5, 7.5, 12.5 mol%) glasses doped with Eu3+ ions in 1mol% are fabricated by the melting method. The Fourier transform infrared (FTIR) spectra, phonon sideband spectra, emission and excitation spectra of the glasses are measured. The crystal field parameter and coordination number of Eu3+ ions in the glasses are obtained according to the splitting of their 5D0 - 7F1levels. The intensity parameters Ω2 and Ω4 of Eu3+ ions for optical transition are calculated from their emission spectra in terms of reduced matrix U(t) (λ= 2,4,6) character for optical transitions. The results indicate that the intensity parameters Ω2 and Ω4 increase with the increase of Nb2O5 content, suggesting that the symmetry becomes lower, the band of Eu and O atoms becomes stronger and the covalence increases with the increase of Nb2O5 content.

  12. 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.)

  13. Sorption properties and reversibility of Ti(IV) and Nb(V)-fluoride doped-Ca(BH{sub 4}){sub 2}-MgH{sub 2} system

    Energy Technology Data Exchange (ETDEWEB)

    Bonatto Minella, Christian, E-mail: christian.minella@kit.edu [Institute for Metallic Materials, IFW Dresden, Helmholtzstrasse 20, D-01069 Dresden (Germany); Technische Universität Dresden, D-01062 Dresden (Germany); Garroni, Sebastiano [Dipartimento di Chimica e Farmacia, Universitá di Sassari and INSTM, Via Vienna 2, I-07100 Sassari (Italy); Pistidda, Claudio [Institute of Materials Research, Materials Technology, Helmholtz-Zentrum Geesthacht, Zentrum für Material- und Küstenforschung GmbH, Max Planck Str. 1, D-21502 Geesthacht (Germany); Baró, Maria Dolors [Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Gutfleisch, Oliver [Materials Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 16, 64287 Darmstadt (Germany); Klassen, Thomas; Dornheim, Martin [Institute of Materials Research, Materials Technology, Helmholtz-Zentrum Geesthacht, Zentrum für Material- und Küstenforschung GmbH, Max Planck Str. 1, D-21502 Geesthacht (Germany)

    2015-02-15

    Highlights: • Faster desorption reaction for doped materials vs. the pure composite system. • Kinetic improvement concerning re-hydrogenation reaction showed by the addition of NbF{sub 5}. • Full characterization of the de-hydrogenation reaction pathway by means of both SR-PXD and {sup 11}B{"1H} MAS-NMR. • Study of the evolution of the chemical state of the additives upon both milling and sorption reactions. - Abstract: In the last decade, alkaline and alkaline earth metal tetrahydroborates have been the focuses of the research due to their high gravimetric and volumetric hydrogen densities. Among them, Ca(BH{sub 4}){sub 2} and the Ca(BH{sub 4}){sub 2} + MgH{sub 2} reactive hydride composites (RHC), were calculated to have the ideal thermodynamic properties which fall within the optimal range for mobile applications. In this study, the addition of NbF{sub 5} or TiF{sub 4} to the Ca(BH{sub 4}){sub 2} + MgH{sub 2} reactive hydride composite system was attempted aiming to obtain a full reversible system with the simultaneous suppression of CaB{sub 12}H{sub 12}. Structural characterization of the specimens was performed by means of in-situ Synchrotron Radiation Powder X-ray diffraction (SR-PXD) and {sup 11}B{"1H} Solid State Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR). The evolution of the chemical state of the Nb- and Ti-based additives was monitored by X-ray Absorption Near Edge Structure (XANES). The addition of NbF{sub 5} or TiF{sub 4} to the Ca(BH{sub 4}){sub 2} + MgH{sub 2} system have not suppressed completely the formation of CaB{sub 12}H{sub 12} and only a slight improvement concerning the reversible reaction was displayed just in the case of Nb-doped composite material.

  14. 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.

  15. Surface energy effects on the stability of anatase and rutile nanocrystals: A predictive diagram for Nb2O5-doped-TiO2

    Science.gov (United States)

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

    2017-01-01

    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. Nb2O5 is commonly added to TiO2 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 Nb2O5-doped TiO2. 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.

  16. Effect of hot-filament annealing in a hydrogen atmosphere on the electrical and structural properties of Nb-doped TiO{sub 2} sputtered thin films

    Energy Technology Data Exchange (ETDEWEB)

    Tavares, C.J., E-mail: ctavares@fisica.uminho.pt [Centre of Physics, University of Minho, 4710-057 Braga (Portugal); Castro, M.V.; Marins, E.S.; Samantilleke, A.P.; Ferdov, S.; Rebouta, L.; Benelmekki, M.; Cerqueira, M.F.; Alpuim, P. [Centre of Physics, University of Minho, 4710-057 Braga (Portugal); Xuriguera, E. [Dept. Ciencia dels Materials, Universitat de Barcelona, Barcelona (Spain); Riviere, J.-P.; Eyidi, D.; Beaufort, M.-F. [Institut P' , University of Poitiers, Bat. SP2MI, Bd. Pierre et Marie Curie, BP 30179, 86962 Futuroscope (France); Mendes, A. [Laboratory of Process, Environment and Energy Engineering (LEPAE), Chemical Engineering Department, Faculty of Engineering, University of Porto, 4200-465 Porto (Portugal)

    2012-01-31

    In this work Nb-doped TiO2 thin films were deposited by d.c.-pulsed reactive magnetron sputtering at 500 Degree-Sign C from a composite target with weight fractions of 96% Ti and 4% Nb, using oxygen as reactive gas. In order to enhance the conductive properties, the as-deposited samples were treated in vacuum with atomic hydrogen at a substrate temperature of 500 Degree-Sign C. The atomic hydrogen flow was generated by a hot filament, inside a high-vacuum chemical vapour deposition reactor, at a temperature of 1750 Degree-Sign C. In order to optimise the hydrogen hot-wire treatments, the H{sub 2} pressure was varied between 1.3 and 67 Pa, the treatment time was monitored between 1 and 5 min and the hot-filament current was changed between 12 and 17 A. Dark conductivity was measured as a function of temperature and its value at room temperature was extrapolated and used to assess the effect of the hydrogen annealing on the charge transport properties. A two-order of magnitude increase in dark conductivity was typically observed for optimised hydrogen treatments (10 Pa), when varying the hydrogen pressure, resulting in a minimum resistivity of {approx} 3 Multiplication-Sign 10{sup -3} {Omega} cm at room temperature. The maximum amount of atomic H incorporation in oxygen vacancies was determined to be {approx} 5.7 at.%. Carrier mobility and resistivity were also investigated using Hall effect measurements. Correlations between structural and electrical properties and the hydrogen treatment conditions are discussed. The purpose of these films is to provide a transparent and conductive front contact layer for a-Si based photovoltaics, with a refractive index that better matches that of single and tandem solar cell structures. This can be achieved by an appropriate incorporation of a very small amount of cationic doping (Nb{sup 5+}) into the titanium dioxide lattice.

  17. Computational Study of Nb-Doped-SnO2/Pt Interfaces: Dopant Segregation, Electronic Transport, and Catalytic Properties

    DEFF Research Database (Denmark)

    Fu, Qiang; Halck, Niels Bendtsen; Hansen, Heine Anton

    2017-01-01

    in the subsurface layers of the NTO substrate, whereas their transport across the Pt/NTO interface is hindered by a high thermodynamic barrier under the operating condition of PEMFCs. The interfacial transport of Sn is, however, more facile, indicating possible formations of Sn Pt alloys and tin oxides...... functional theory and non equilibrium Green's function study, we investigate the Nb segregation at Pt/NTO interfaces under operational electrochemical conditions, and reveal the resulting effects on the electronic transport, as well as the catalytic properties. We find that the Nb dopants tend to aggregate....... The electronic conductivities of the Pt/NTO systems are not particularly sensitive to the distance of the Nb dopants relative to the interface, but depend explicitly on the Nb concentration and configuration. Through a dopant induced ligand effect, the NTO substrates can improve the catalytic activity of the Pt...

  18. Adsorption and Reaction of CO on (100) Surface of SrTiO3 by Density Function Theory Calculation

    Institute of Scientific and Technical Information of China (English)

    YUN Jiang-Ni; ZHANG Zhi-Yong; ZHANG Fu-Chun

    2008-01-01

    Adsorption and reaction of CO on two possible terminations of SrTi03 (100) surface are investigated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory. The adsorption energy, Mulliken population analysis, density of states (DOS) and electronic density difference of CO on SrTi03 (100) surface, which have never been investigated before as far as we know are performed. The calculated results reveal that the Ti-CO orientation is the most stable configuration and the adsorption energy (0.449eV) is quite small. CO molecules adsorb weakly on the SrTiO3 (100) surface, there is predominantly electrostatic attraction between CO and the surface rather than a chemical bonding mechanism.

  19. Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Bi, Feng; Huang, Mengchen; Ryu, Sangwoo; Lee, Hyungwoo; Bark, Chung-Wung; Eom, Chang-Beom; Irvin, Patrick; Levy, Jeremy

    2014-09-01

    Reports of emergent conductivity, superconductivity and magnetism have helped to fuel intense interest in the rich physics and technological potential of complex-oxide interfaces. Here we employ magnetic force microscopy to search for room-temperature magnetism in the well-studied LaAlO3/SrTiO3 system. Using electrical top gating to control the electron density at the oxide interface, we directly observe the emergence of an in-plane ferromagnetic phase as electrons are depleted from the interface. Itinerant electrons that are reintroduced into the interface align antiferromagnetically with the magnetization at first screening and then destabilizing it as the conductive regime is approached. Repeated cycling of the gate voltage results in new, uncorrelated magnetic patterns. This newfound control over emergent magnetism at the interface between two non-magnetic oxides portends a number of important technological applications.

  20. High charge carrier density at the NaTaO3/SrTiO3 hetero-interface

    KAUST Repository

    Nazir, Safdar

    2011-08-05

    The formation of a (quasi) two-dimensional electron gas between the band insulators NaTaO3 and SrTiO3 is studied by means of the full-potential linearized augmented plane-wave method of density functional theory. Optimization of the atomic positions points to only small changes in the chemical bonding at the interface. Both the p-type (NaO)−/(TiO2)0 and n-type (TaO2)+/(SrO)0 interfaces are found to be metallic with high charge carrier densities. The effects of O vacancies are discussed. Spin-polarized calculations point to the formation of isolated O 2pmagnetic moments, located in the metallic region of the p-type interface.

  1. Structural conditions that leads to photoluminescence emission in SrTiO3: An experimental and theoretical approach

    Science.gov (United States)

    Longo, V. M.; de Figueiredo, A. T.; de Lázaro, S.; Gurgel, M. F.; Costa, M. G. S.; Paiva-Santos, C. O.; Varela, J. A.; Longo, E.; Mastelaro, V. R.; DE Vicente, F. S.; Hernandes, A. C.; Franco, R. W. A.

    2008-07-01

    Complex cluster [TiO5ṡVOz] and [SrO11ṡVOz] (where VOz=VOX, VO•, VO••) vacancies were identified in disordered SrTiO3 powders prepared by the polymeric precursor method, based on experimental measurements by x-ray absorption near edge structure spectroscopy. The paramagnetic complex states of [TiO5ṡVO•] and [SrO11ṡVO•] with unpaired electrons were confirmed by electron paramagnetic resonance spectroscopy. The disordered powders showed strong photoluminescence at room temperature. Structural defects of disordered powders, in terms of band diagram, density of states, and electronic charges, were interpreted using high-level quantum mechanical calculations in the density functional framework. The four periodic models used here were consistent with the experimental data and explained the presence of photoluminescence.

  2. Formation of Sr adatom chains on SrTiO3 (1 1 0) surface determined by strain

    Science.gov (United States)

    Liang, Yan; Li, Fengmiao; Wang, Weihua; Yang, Hao; Guo, Jiandong

    2016-09-01

    The adsorption behavior of Sr adatoms on the SrTiO3 (1 1 0)-(4  ×  1) reconstructed surface with Ti2O3 vacancies distributed in a superstructure is studied by scanning tunneling microscopy and density functional theory calculations. With the adsorption amount increasing, all the Sr adatoms between adjacent Ti2O3 vacancies are closely packed along the quasi-1D stripes on the surface with a uniform separation from each other. The formation of such adatom chains is determined by the surface strain relief—the local lattice relaxations in response to Sr adatoms and Ti2O3 vacancies are incompatible, leading to the strong repulsive interaction between them. Consequently the distribution of Sr chains follows the long-range order of the growth template with their length tunable in a certain range by evaporation amount.

  3. High mobility of the strongly confined hole gas in AgTaO3/SrTiO3

    KAUST Repository

    Nazir, Safdar

    2012-05-18

    A theoretical study of the two-dimensional hole gas at the (AgO)−/(TiO2)0 p-type interface in the AgTaO3/SrTiO3 (001) heterostructure is presented. The Ag 4d states strongly hybridize with the O 2p states and contribute to the hole gas. It is demonstrated that the holes are confined to an ultra thin layer (∼4.9Å) with a considerable carrier density of ∼1014cm−2. We estimate a hole mobility of 18.6 cm2 V−1 s−1, which is high enough to enable device applications.

  4. Role of O defects at the BiMnO3/SrTiO3 interface

    Science.gov (United States)

    Jilili, J.; Cossu, F.; Schwingenschlögl, U.

    2016-08-01

    We use first principles calculations to study ideal and O deficient BiMnO3/SrTiO3 superlattices. The ideal superlattice is characterized by parallel alignment of the Mn and Ti magnetic moments at the n-interface, while an antiparallel alignment has been reported experimentally. O defects at the n-interface are found to favor the MnO2 and BiO layers over the TiO2 layer. The band gap of the superlattice is strongly reduced when the MnO2 layer is O deficient and {d}3{z2-{r}2} states are observed at the Fermi energy when the BiO layer is O deficient. Only in the latter case the Mn and Ti magnetic moments at the n-interface align antiparallel. Therefore, O defects in the BiO layer turn out to be essential for reproducing the experimental interface magnetism and for understanding its mechanism.

  5. Glass and glass-ceramics along the SrTiO3-NaPO3 line

    Directory of Open Access Journals (Sweden)

    Sinouh H.

    2013-09-01

    Full Text Available The xSrTiO3-(1−xNaPO3 (x = 0−0.20 mol% glasses were prepared by the conventional melt-quenching method. The amorphous state of the samples was verified by X-ray diffraction. The glass-ceramic materials were obtained by the well known thermal controlled crystallization process. It is found that several physical properties such as the density, molar volume, and the glass transition temperature depend strongly on the chemical composition. Vickers test on the glasses showed that the micro-hardness increases with the SrTiO3 content. The structural approach of the glasses was realized by IR spectroscopy. This technique has highlighted the co-existence of different phosphate and titanium structural units in the glassy-matrix. Crystallization of the glasses was enhanced by heat treatments and followed by X-ray diffraction. A mechanism for this glass crystallization was proposed.

  6. Study of Electron Distribution and Magnetism at the Relaxed SrTiO3/LaAlO3 Interface

    Science.gov (United States)

    Ghosh, Soham; Manousakis, Efstratios

    2014-03-01

    The presence of a two-dimensional electron gas (2DEG) at the interface between two insulators SrTiO3 and LaAlO3 makes it an interesting topic of condensed matter research. It exhibits a variety of properties such as high mobility, magnetism and superconductivity. Bandstructure calculations have linked the presence of the electon gas to polar catastrophe and oxygen vacancy, but the value of the carrier density and its distribution is a matter of debate. In the present work, we use Density Functional Theory to study the electron density distribution and the effect of ionic relaxations on the properties of the 2DEG. In order to understand the nature of magnetism, we construct localized Wannier functions from Bloch states given by DFT and use them to calculate hopping matrix elements and exchange integrals, which act as parameters in a model to understand electron-electron correlation at the interface.

  7. Photoinduced modulation and relaxation characteristics in LaAlO3/SrTiO3 heterointerface

    KAUST Repository

    Jin, K. X.

    2015-03-05

    We report the modulation and relaxation characteristics in the two-dimensional electron gas system at LaAlO3/SrTiO3 heterointerface induced by the ultraviolet light illumination (365 nm). The suppression of Kondo effect at the interface illuminated by the light originates from the light irradiation-induced decoherence effect of localized states. It is interesting to note that the persistent and transient photoinduced effects are simultaneously observed and the photoinduced maximum change values in resistance are 80.8% and 51.4% at T = 20 K, respectively. Moreover, the photoinduced relaxation processes after the irradiation are systematically analyzed using the double exponential model. These results provide the deeper understanding of the photoinduced effect and the experimental evidence of tunable Kondo effect in oxides-based two-dimensional electron gas systems.

  8. Dielectric and Structural Properties of SrTiO_3 Thin Films Grown by Laser Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Dielectric and Structural Properties of SrTiO_3 Thin Films Grown by Laser Molecular Beam Epitaxy[1]Hao J H,Gao J,Wang Z,et al.Interface structure and phase of epitaxial SrTi O3(110)thin fil ms grown directly on silicon[J].Appl Phys Lett,2005,87:131908. [2]Hao J H,Gao J,Wang HK.SrTi O3(110)thin fil ms grown directly on different oriented silicon substrates[J].Appl Phys A,2005,81:1233. [3]Aki mov I A,Sirenko A A,Clark A M,et al.Electric-field-induced soft-mode hardening in SrTi O3fil ms[J].Phys Rev Lett...

  9. Tunable Electron-Electron Interactions in LaAlO_{3}/SrTiO_{3} Nanostructures

    Directory of Open Access Journals (Sweden)

    Guanglei Cheng

    2016-12-01

    Full Text Available The interface between the two complex oxides LaAlO_{3} and SrTiO_{3} has remarkable properties that can be locally reconfigured between conducting and insulating states using a conductive atomic force microscope. Prior investigations of “sketched” quantum dot devices revealed a phase in which electrons form pairs, implying a strongly attractive electron-electron interaction. Here, we show that these devices with strong electron-electron interactions can exhibit a gate-tunable transition from a pair-tunneling regime to a single-electron (Andreev bound state tunneling regime where the interactions become repulsive. The electron-electron interaction sign change is associated with a Lifshitz transition where the d_{xz} and d_{yz} bands start to become occupied. This electronically tunable electron-electron interaction, combined with the nanoscale reconfigurability of this system, provides an interesting starting point towards solid-state quantum simulation.

  10. Surface potential distribution of a LaAlO3 film on mixed termination SrTiO3

    Science.gov (United States)

    Jang, Yun Hyeong; Cho, Jin Hyung

    2016-09-01

    Scanning probe microscope (SPM) is used to investigate the morphology and the electric properties of the surface, as well as the interface, of LaAlO3/SrTiO3 (LAO/STO) films. To establish the physical properties of the heteroepitaxial oxide interface, we characterized single- and mixed-termination of the STO substrates by using nanoscopic measurements of the electric and the structural properties, as well as the LAO film grown on the mixed-terminated STO substrates. In the case of the LAO film grown on the low-miscut STO substrate, the surface potential only showed a difference at the step edge while the LAO film on the high-miscut STO substrate showed a considerable change in the surface potential distribution at the region in which step bunching has occurred. In the poling experiment, a significant rise in the surface potential difference is observed after writing of the DC bias.

  11. Tunnel and electrostatic coupling in graphene-LaAlO3/SrTiO3 hybrid systems

    Directory of Open Access Journals (Sweden)

    I. Aliaj

    2016-06-01

    Full Text Available We report on the transport properties of hybrid devices obtained by depositing graphene on a LaAlO3/SrTiO3 oxide junction hosting a 4 nm-deep 2-dimensional electron system. At low graphene-oxide inter-layer bias, the two electron systems are electrically isolated, despite their small spatial separation. A very efficient reciprocal gating of the two neighboring 2-dimensional systems is shown. A pronounced rectifying behavior is observed for larger bias values and ascribed to the interplay between electrostatic field-effects and tunneling across the LaAlO3 barrier. The relevance of these results in the context of strongly coupled bilayer systems is discussed.

  12. Imaging pulsed laser deposition growth of homo-epitaxial SrTiO3 by low-energy electron microscopy

    Science.gov (United States)

    van der Torren, A. J. H.; van der Molen, S. J.; Aarts, J.

    2016-12-01

    By combining low-energy electron microscopy with in situ pulsed laser deposition we have developed a new technique for film growth analysis, making use of both diffraction and real-space information. Working at the growth temperature, we can use: the intensity and profile variations of the specular beam to follow the coverage in a layer-by-layer fashion; real-space microscopy to follow e.g. atomic steps at the surface; and electron reflectivity to probe the unoccupied band structure of the grown material. Here, we demonstrate our methodology for homo-epitaxial growth of SrTiO3. Interestingly, the same combination of techniques will also be applicable to hetero-epitaxial oxide growth, largely extending the scope of research possibilities.

  13. Tunable Electron-Electron Interactions in LaAlO3/SrTiO3 Nanostructures

    Science.gov (United States)

    Cheng, Guanglei; Tomczyk, Michelle; Tacla, Alexandre B.; Lee, Hyungwoo; Lu, Shicheng; Veazey, Josh P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Eom, Chang-Beom; Daley, Andrew; Pekker, David; Levy, Jeremy

    2016-10-01

    The interface between the two complex oxides LaAlO3 and SrTiO3 has remarkable properties that can be locally reconfigured between conducting and insulating states using a conductive atomic force microscope. Prior investigations of "sketched" quantum dot devices revealed a phase in which electrons form pairs, implying a strongly attractive electron-electron interaction. Here, we show that these devices with strong electron-electron interactions can exhibit a gate-tunable transition from a pair-tunneling regime to a single-electron (Andreev bound state) tunneling regime where the interactions become repulsive. The electron-electron interaction sign change is associated with a Lifshitz transition where the dx z and dy z bands start to become occupied. This electronically tunable electron-electron interaction, combined with the nanoscale reconfigurability of this system, provides an interesting starting point towards solid-state quantum simulation.

  14. Structural and magnetic properties of CoTiO3 thin films on SrTiO3 (001)

    Science.gov (United States)

    Schoofs, Frank; Egilmez, Mehmet; Fix, Thomas; MacManus-Driscoll, Judith L.; Blamire, Mark G.

    2013-04-01

    CoTiO3 (CTO) thin films were grown on single crystal SrTiO3 (STO) (001) substrates by pulsed laser deposition, with thicknesses ranging between 2.6 and 25 nm. Two-dimensional growth is observed up to a thickness of 2 unit cells, but then the film partially relaxes with CTO [100] oriented parallel to STO [110] and CTO [001] oriented parallel to the STO [001]. Magnetic characterization of our films revealed an enhancement of the antiferromagnetic Néel temperature (to ˜53 K) when compared to the bulk (38 K). This is attributed to a tensile c-axis strain as evidenced from x-ray diffraction measurements.

  15. Structural and optical properties of low energy nitrogen ion implanted SrTiO3 thin films

    Science.gov (United States)

    Kumar, Vishnu; Asokan, K.; Annapoorni, S.

    2017-05-01

    The effect of 60 keV nitrogen ion implantation on the structural and optical properties of strontium titanate, SrTiO3 (STO) thin films were investigated as a function of ion fluences. These thin films were deposited on quartz substrates using RF magnetron sputtering and annealed at 750 °C for 5 hours. It was observed that the intensity of the X-Ray Diffraction (XRD) peaks increase at lower ion fluence and then decrease at higher ion fluences. The band gap derived from the UV-Visible spectrum of annealed pristine film was estimated to be 3.62 eV. A slight increase in the band gap was observed after N ion implantation.

  16. Spin-orbit coupled superconductivity at the interface of LaAlO3/SrTiO3

    Science.gov (United States)

    Li, Chi-Sheng; Singh, Akhilesh Kr.; Song, Ming-Yuan; Lee, Wei-Li

    2017-03-01

    We have grown few unit cells of epitaxial LaAlO3 (LAO) on TiO2 terminated SrTiO3 (STO) substrates using oxide MBE technique, which shows an interface superconductivity below about 0.3 K. By fabricating a back gate electrode via the STO substrate, the superconductor-to-insulator transition was observed by applying gate voltages on a macroscopic size of the two-dimensional electron liquid (2DEL) at the interface of LAO/STO. From the superconducting critical field anisotropy measurements, a sizable spin-orbit coupling is found to present in the superconducting phase, where the upper limit of the spin-orbit coupling strength can be largely tuned by gate voltages. In addition, magnetotransport anomaly was observed when depleting the electron density and thus driving the 2DEL into insulating phase, suggesting an inhomogeneous density distribution and also a possible multiband conduction in the 2DEL.

  17. Direct observation of the spatial and temporal dynamics of polaron diffusion in SrTiO3

    Science.gov (United States)

    Kohmoto, T.; Ikeda, D.; Liang, X.; Moriyasu, T.

    2013-06-01

    The generation, relaxation, and diffusion dynamics of optically induced lattice distortion in the relaxed excited state of SrTiO3 are studied by using polarization spectroscopy with the pump-probe technique. The relaxed excited state is generated with a rise time on the order of 100 ps. Three kinds of thermal activation processes of the localized lattice distortion are found, and these processes are considered to be caused by photogenerated carriers in trapped states, which play important roles in photoluminescence or photoconductivity. We observed the lattice distortion induced by a separated pump beam from the probe beam to investigate its itineracy. The lattice-distortion signal appears later as the separation along the [100] axis becomes larger. The temperature dependence of the mobility suggests that the observed diffusive lattice distortion is caused by photogenerated electrons accompanied by lattice distortion, or electron polarons. Thus, the spatial and temporal dynamics of polaron diffusion were observed directly in our experiment.

  18. Thermodynamic equilibrium studies of nanocrystallite SrTiO3 grain boundaries by high temperature photoelectron spectroscopy

    Institute of Scientific and Technical Information of China (English)

    刘振祥; 谢侃

    2000-01-01

    Nanostructured strontium titanate (SrTiO3) thin films are studied by high temperature pho-toelectron spectroscopy and thermal gravimetric analysis. The results indicate that ion migration and redistribution as well as transformation between lattice oxygen and gas phase oxygen take place near the grain boundaries during thermodynamic equilibrium process, which lead to obvious variation of the surface composition with temperature. The lattice oxygen ions migrate from bulk to grain surface with temperature rising up; meanwhile Ti ions also migrate to grain surface and combine with oxygen ions forming Ti-O complex. An opposite process takes place during temperature falling down, but the latter process is much slower than the former one. A primary model is proposed to explain this phenomenon.

  19. Thermodynamic equilibrium studies of nanocrystallite SrTiO3 grain boundaries by high temperature photoelectron spectroscopy

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Nanostructured strontium titanate (SrTiO3) thin films are studied by high temperature photoelectron spectroscopy and thermal gravimetric analysis. The results indicate that ion migration and redistribution as well as transformation between lattice oxygen and gas phase oxygen take place near the grain boundaries during thermodynamic equilibrium process, which lead to obvious variation of the surface composition with temperature. The lattice oxygen ions migrate from bulk to grain surface with temperature rising up; meanwhile Ti ions also migrate to grain surface and combine with oxygen ions forming Ti-O complex. An opposite process takes place during temperature falling down, but the latter process is much slower than the former one. A primary model is proposed to explain this phenomenon.

  20. Photocatalytic reduction of CO2 by CuxO nanocluster loaded SrTiO3 nanorod thin film

    Science.gov (United States)

    Shoji, Shusaku; Yin, Ge; Nishikawa, Masami; Atarashi, Daiki; Sakai, Etsuo; Miyauchi, Masahiro

    2016-08-01

    Photocatalytic carbon dioxide (CO2) conversion into carbon monoxide (CO) using H2O as an electron donor was achieved by the strontium titanate (SrTiO3: STO) nanorod thin films loaded with amorphous copper oxide (CuxO) nanoclusters. The loading of the CuxO-cocatalysts onto STO nanorods clearly improved the photocatalytic activity compared to bare STO nanorods. The CuxO-cocatalysts are composed of abundant and non-toxic elements, and can be loaded by using a simple and economical method. Our findings demonstrate that CuxO nanoclusters function as a general cocatalyst and can be used in combination with various semiconductors to construct low-cost and efficient photocatalytic CO2 reduction systems.

  1. Phase segregation of superconductivity and ferromagnetism at the LaAlO3/SrTiO3 interface.

    Science.gov (United States)

    Mohanta, N; Taraphder, A

    2014-01-15

    The highly conductive two-dimensional electron gas formed at the interface between insulating SrTiO3 and LaAlO3 shows low-temperature superconductivity coexisting with inhomogeneous ferromagnetism. The Rashba spin-orbit interaction with the in-plane Zeeman field of the system favors p(x) ± ip(y)-wave superconductivity at finite momentum. Owing to the intrinsic disorder at the interface, the role of spatial inhomogeneity in the superconducting and ferromagnetic states becomes important. We find that, for strong disorder, the system breaks up into mutually excluded regions of superconductivity and ferromagnetism. This inhomogeneity-driven electronic phase separation accounts for the unusual coexistence of superconductivity and ferromagnetism observed at the interface.

  2. Effect of Nb5+doping on high rate performance of LiFePO4%掺Nb5+对LiFePO4高倍率性能的影响

    Institute of Scientific and Technical Information of China (English)

    唐红; 郭孝东; 刘恒; 唐艳; 钟本和

    2011-01-01

    以三价铁(Fe2O3)为铁源,采用半固相-碳热还原法制备UFePO4/C正极材料,对LiFePO4的铁位进行高价金属离子(Nb5+)掺杂制得LiFe1-xNbxPO4/C(x=0、0.01、0.03、0.05、0.07)复合正极材料.X射线衍射分析材料的晶型结构发现掺杂一定量的金属离子不会改变材料的晶型结构.对材料进行充放电循环性能测试表明,掺入高价金属离子会改善材料的电化学性能,其放电比容量有显著提高,循环稳定性也得到一定改善,同没有掺杂金属离子的LiFePO4/C相比尤其在大电流方面的优势更加明显.其中掺铌0.03的材料性能最好,在0.1 C放电倍率下.首次放电比容量可以达到160.57 mAh/g,1 C时首次放电比容量仍有136.43 mAh/g,而在大倍率10 C放电时,还保持在95 mAh/g.%LiFePO4/C cathode material was prepared by semi-solid phase-carbon-thermal reduction method, using ferric (Fe2O3) as Fe source, LiFe1-xNbxPO4/C(x=0,0.01,0.03,0.05,0.07) composite cathode materials were obtained with high-priced metal ions (Nb5+) doped in Fe site. X-ray diffraction analysis of the crystalline structure of samples indicates that, doping a certain amount of metal ions does not change the crystalline structure of materials. The charge-discharge cycle performance tests show that, doping high-priced ions can improve the electrochemical properties of materials. The specific discharge capacity of the samples is improved greatly and cycling stability is also improved to some extent. Especially in large current field, the advantages am more obvious compared with no metal ions doped LiPePO4/C. LiFePO4/C sample doped with 3% Nb5+ has the best performance, and the first discharge specific capacity is 160.57 mAh/g at 0.1 C, which is still 136.43 mAh/g at 1 C, while at 10 C, the discharge specific capacity still maintains 95 mAh/g.

  3. Transition metal substituted SrTiO3 perovskite oxides as promising functional materials for oxygen sensor

    Science.gov (United States)

    Misra, Sunasira

    2012-07-01

    Modern industries employ several gases as process fluids. Leakage of these gases in the operating area could lead to undesirable consequences. Even in chemical industries, which use large quantities of inert gases in confined areas, accidental leakage of these process gases would result in the reduction of oxygen partial pressure in atmospheric air. For instance, large amounts of gaseous nitrogen and argon are used in pharmaceutical industries, gas filling/bottling plants, operating area of Fast Breeder reactors, etc. Fall of concentration of oxygen in air below 17% could lead to life risk (Asphyxiation) of the working personnel that has to be checked well in advance. Further, when the leaking gas is of explosive nature, its damage potential would be very high if its concentration level in air increases beyond its lower explosive limit. Surveillance of the ambient within these industries at the critical areas and also in the environment around them for oxygen therefore becomes highly essential. Sensitive and selective gas sensors made of advanced materials are required to meet this demand of monitoring environmental pollution. The perovskite class of oxides (ABO3) is chemically stable even at high temperatures and can tolerate large levels of dopants without phase transformations. The electronic properties of this parent functional material can be tailored by adding appropriate dopants that exhibit different valence states. Aliovalent transition metal substituted SrTiO3 perovskites are good mixed ionic and electronic conductors and potential candidates for sensing oxygen at percentage level exploiting their oxygen pressure dependent electrical conductivity. This paper presents the preparation, study of electrical conductivity and oxygen-sensing characteristics of iron and cobalt substituted SrTiO3.

  4. Band bending and alignment at the spinel/perovskite γ−Al2O3/SrTiO3 heterointerface

    DEFF Research Database (Denmark)

    Schütz, P.; Pfaff, F.; Scheiderer, P.;

    2015-01-01

    We present a comprehensive study of the band bending and alignment at the interface of γ -Al2O3/SrTiO3 heterostructures by hard x-ray photoelectron spectroscopy. Ourmeasurements find no signs for a potential gradient within the polar γ -Al2O3 film as predicted by the basic electronic reconstruction...

  5. A nano-grid structure made of perovskite SrTiO3 nanowires for efficient electron transport layers in inverted polymer solar cells

    Science.gov (United States)

    Kim, Jeong Won; Suh, Yo-Han; Lee, Chang-Lyoul; Kim, Yong Seok; Kim, Won Bae

    2015-02-01

    A nano-grid structure of perovskite SrTiO3 NWs is developed for a novel electron transport layer in inverted polymer solar cells. Due to the excellent charge transporting properties of the SrTiO3 nano-grid structure, the device employing this nanostructure showed ~32% enhanced photovoltaic performance, compared to the solar cell using a TiO2 thin film.A nano-grid structure of perovskite SrTiO3 NWs is developed for a novel electron transport layer in inverted polymer solar cells. Due to the excellent charge transporting properties of the SrTiO3 nano-grid structure, the device employing this nanostructure showed ~32% enhanced photovoltaic performance, compared to the solar cell using a TiO2 thin film. Electronic supplementary information (ESI) available: Experimental details, HR-TEM images with EDX atomic ratio analysis, FE-SEM images, transmittance spectra and light absorbance spectra. See DOI: 10.1039/c4nr06720g

  6. Hard x-ray photoemission and density functional theory study of the internal electric field in SrTiO3/LaAlO3 oxide heterostructures

    NARCIS (Netherlands)

    Slooten, E.; Zhong, Z.C.; Molegraaf, H.J.A.; Eerkes, P.D.; Jong, de S.; Massee, F.; Heumen, E.; Kruize, M.K.; Wenderich, S.; Kleibeuker, J.E.; Gorgoi, M.; Hilgenkamp, J.W.M.; Brinkman, A.; Huijben, M.; Rijnders, A.J.H.M.; Blank, D.H.A.; Koster, G.; Kelly, P.J.; Golden, M.S.

    2013-01-01

    A combined experimental and theoretical investigation of the electronic structure of the archetypal oxide heterointerface system LaAlO3 on SrTiO3 is presented. High-resolution, hard x-ray photoemission is used to uncover the occupation of Ti 3d states and the relative energetic alignment—and hence i

  7. Laser molecular-beam epitaxy and second-order optical nonlinearity of BaTiO3/SrTiO3 superlattices

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3 (100) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface. The relationship between the second-order nonlinear optical susceptibilities and the superlattice structure was systematically studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk BaTiO3 crystal. The mechanism of the enhancement of the second-order optical nonlinearity was discussed by taking into account the stress-induced lattice distortion and polarization enhancement.

  8. Magnetic anisotropy and magnetization reversal of La 0.67 Sr 0.33 MnO 3 thin films on SrTiO 3 (110)

    NARCIS (Netherlands)

    Boschker, Hans; Kautz, Jaap; Houwman, Evert P.; Koster, Gertjan; Blank, Dave H.A.; Rijnders, Guus

    2010-01-01

    The magnetic behavior of La 0.67 Sr 0.33 MnO 3 (LSMO) filmsgrown on SrTiO 3 (110) substrates was studied. In-plane uniaxial magnetic anisotropy with the easy axis aligned with the [001] lattice direction was observed, together with an out-of-plane component. This is explained by the crystal stru

  9. Controlling interfacial states in amorphous/crystalline LaAlO3/SrTiO3 heterostructures by electric fields

    DEFF Research Database (Denmark)

    Christensen, Dennis; Trier, Felix; Chen, Yunzhong;

    2013-01-01

    amorphous LaAlO3 films on SrTiO3. Here, we present a non-volatile and reversible tuning of the interface conductivity by more than 3 orders of magnitude at room temperature by applying an electric field to such amorphous/crystalline heterostructures with amorphous LaAlO3 film thicknesses of 2 nm. We show...

  10. Interface structure of SrTiO3-LaAlO3 at elevated temperatures studied in-situ by synchroton x-rays

    NARCIS (Netherlands)

    Vonk, V.; Huijben, Mark; Driessen, K.J.I.; Tinnemans, P.; Brinkman, Alexander; Harkema, Sybolt; Graafsma, H; Graafsma, H.

    2007-01-01

    The atomic interface structure between SrTiO3 and LaAlO3 was studied at elevated temperatures employing in situ surface x-ray diffraction. The results at 473 K indicate that the lattice distorts significantly in two ways. First, the interatomic distances between the cations across the interface

  11. Strain-induced structural changes in thin YBa2Cu3O7-x films on SrTiO3 substrates

    NARCIS (Netherlands)

    Vonk, V.; van Reeuwijk, S.J.; Dekkers, Jan M.; Harkema, Sybolt; Rijnders, Augustinus J.H.M.; Graafsma, H.; Graafsma, H

    2004-01-01

    High-energy synchrotron radiation is used to obtain reciprocal space maps of thin YBa2Cu3O7−x films grown by pulsed laser deposition on (001) SrTiO3 substrates. The films show a transition from a tetragonal to an orthorhombic structure with increasing film thickness. The critical thickness is found

  12. Infrared ellipsometry study of the confined electrons in a high-mobility γ-Al2O3/SrTiO3 heterostructure

    DEFF Research Database (Denmark)

    Yazdi-Rizi, M.; Marsik, P.; Mallett, B. P. P.

    2016-01-01

    With infrared ellipsometry we studied the response of the confined electrons in γ-Al2O3/SrTiO3 (GAO/STO) heterostructures in which they originate predominantly from oxygen vacancies. From the analysis of a so-called Berreman mode, that develops near the highest longitudinal optical phonon mode of...

  13. Imposed quasi-layer-by-layer homoepitaxial growth of SrTiO3 films by large area pulsed laser deposition

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Pryds, Nini

    2011-01-01

    The homoepitaxial growth of SrTiO3 (STO) films was investigated by a large-area pulsed laser deposition (PLD), which was in-situ monitored by a high pressure reflective high energy electron diffraction. By combining a conventionally continuous film deposition with a followed interval relaxation, ...

  14. Propriedades dielétricas de cerâmicas (Sr,BaNb2O6 dopadas com terras raras Dielectric properties of (Sr,BaNb2O6 ceramics doped with rare earths

    Directory of Open Access Journals (Sweden)

    I. A. Santos

    1999-12-01

    Full Text Available Cerâmicas de Sr1-xBaxNb2O6, "puras" e dopadas com óxidos de terras raras, foram preparadas com o objetivo de estudar o seu comportamento dielétrico em função da adição desses dopantes. As amostras foram caracterizadas através de medidas dielétricas efetuadas em função da temperatura (30 K a 500 K e da freqüência (1 kHz a 1 MHz. Em todas as amostras estudadas verifica-se a presença de dois processos distintos de relaxação dielétrica. O primeiro processo é observado a temperaturas inferiores a 100 K. O segundo processo é observado próximo a temperatura ambiente, onde a constante dielétrica apresenta seu maior valor. Observou-se que a adição de dopantes causa efeitos distintos nas temperaturas de máximo das constantes dielétricas nas duas regiões de relaxação dielétrica.Ceramics of SBN, undoped and doped with rare earth oxides, were prepared to the study of the influence of the doping on the dielectric properties. The samples were characterised through dielectric measurements as a function of temperature (30 K to 500 K and frequency (1 kHz to 1 MHz. In all samples two distinct dielectric relaxation processes were observed. The first one at temperatures below 100 K; the second one is near room temperature, where the dielectric constant is maximum. The doping causes distinct effects in the maximum temperatures of the dielectric constants in the two dielectric relaxation regions.

  15. Bleaching effect and nonvola-tile holographic storage in doubly doped LiNbO3:Fe:Cu crystals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The bleaching effect, i. e. the crystal shows that decoloration after it is illuminated by ultraviolet light, has been observed in congruent LiNbO3:Fe :Cu crystals. Based on this bleaching effect, a new technique including the reco rding phase by two interfering red beams and fixing phase by both UV light and a coherent red beam has been experimentally investigated to realize nonvolatile holographic storage in LiNbO3:Fe:Cu. The results of proof-of-concept experiments confirm that bleaching effect becomes an alternative physical mechanism for nonv olatile holographic storage with high recording sensitivity and weak light-induced scattering noise.

  16. Study and control of the conductivity of Nb-doped Bi4Ti3O12 for high temperature piezoelectric applications

    Directory of Open Access Journals (Sweden)

    Damjanovic, D.

    1999-12-01

    Full Text Available Bismuth-based layered compounds have been considered during the last years as interesting materials for high temperature piezoelectric applications, due to their stability and wide thermal range of the ferroelectric activity. The high electrical conductivity present at high temperatures has been a disadvantage for the potential applications of these compounds. On Bi4Ti3O12 (BIT, different doping, such as Nb5+ and W6+ were used to increase resistivity. It has been shown that Nb5+ doping modifies piezoelectric response, passing from relatively high hysteretic to linear and almost completely non-hysteretic. In the present work, the effect of Nb5+ doping related to the conduction response is investigated. Studies of the I-V curves as a function of the temperature allows us, for the first time, to measure the conductivity of these compounds at room temperature (RT and to discuss which are the microstructural elements that control the conductivity of the material using a serial electrical model. It is shown that at temperatures between RT and 125ºC the grain boundary conductivity limits the total conductivity. At higher temperatures, the material conducts mainly through the bulk of grains. Conduction type, conductivity thermal regimes and chemical composition may explain the change in the piezoelectric behaviour.Compuestos laminares de bismuto han sido considerados en los últimos años materiales interesantes como piezoeléctricos en aplicaciones de alta temperatura, debido a su estabilidad y amplio rango térmico de existencia de actividad ferroeléctrica. Sin embargo, la elevada conductividad presente a altas temperaturas ha sido una desventaja para las potenciales aplicaciones de estos compuestos. En el caso de Bi4Ti3O12 (BIT, diferentes dopantes como Nb5+ o W6+ han sido empleados para aumentar la resistencia eléctrica del material. Es conocido que el dopado con Nb5+ modifica la respuesta piezoeléctrica del material pasando de presentar una

  17. Resistive switching phenomena of extended defects in Nb-doped SrTiO{sub 3} under influence of external gradients

    Energy Technology Data Exchange (ETDEWEB)

    Rodenbuecher, Christian

    2014-07-01

    Redox-based memristive materials have attracted much attention in the last decade owing to their ability to change the resistance upon application of an electric field making them promising candidates for future non-volatile memories. However, a fundamental understanding of the nature of the resistive switching effect, which is indispensable for designing future technological applications,is still lacking. As a prototype material of a memristive oxide, strontium titanate (SrTiO{sub 3}) has been investigated intensively and it was revealed that the valence change of a Ti ''d'' electron plays an important role during resistive switching related to insulator-to-metal transition. Such a transition can be induced by electrical gradients, by chemical gradients, by a combination of these gradients or by donor doping. Hence, SrTiO{sub 3} doped with the donor Nb should have metallic properties and is used commonly as a conducting substrate for the growth of functional oxide thin films. Nevertheless,the resistive switching effect has also be observed in Nb-doped SrTiO{sub 3}. This paradoxical situation offers a unique opportunity to gain an insight into the processes during the insulator-to metal transition. In this thesis, a comprehensive study of the influence of external gradients on SrTiO{sub 3}:Nb single crystals is presented. The focus is especially set on the investigation of the crystallographic structure, the chemical composition, the electronic structure, the lattice dynamics and the electronic transport phenomena using surface-sensitive methods on the macro- and nanoscale. On the as-received epi-polished single crystals, the evolution of a surface layer having a slight excess of strontium and - in contrast to the bulk of the material - semiconducting properties are observed. Hence, the key for understanding of the resistive switching effect is the knowledge of the nature of the surface layer. On the basis of systematic studies of the influence

  18. Influence of oxygen pressure on the structural, electrical and optical properties of Nb-doped ZnO thin films prepared by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Muying, E-mail: wumy@dgut.edu.cn [School of Electronic Engineering, Dongguan University of Technology, Guangdong Dongguan 523808 (China); Yu, Shihui [School of Electronic and Information Engineering, Tianjin University, Tianjin 300072 (China); He, Lin; Zhang, Geng; Ling, Dongxiong [School of Electronic Engineering, Dongguan University of Technology, Guangdong Dongguan 523808 (China); Zhang, Weifeng [Key Laboratory of Photovoltaic Materials of Henan Province and School of Physics and Electronics, Henan University, Kaifeng 475004 (China)

    2014-02-15

    Nb-doped zinc oxide (NZO) transparent conductive thin films with highly (0 0 2)-preferred orientation were deposited on glass substrates by pulsed laser deposition method in oxygen ambience under different oxygen pressures. The as-deposited films were characterized by X-ray diffraction (XRD), Field emission-scanning electron microscopy (FE-SEM), electrical and optical characterization techniques. It was found that a desirable amount of oxygen can reduce the related defect scattering and enhance the carrier mobility. The resistivity and average optical transmittance of the NZO thin films are of 10{sup −4} Ω cm and over 88%, respectively. The lowest electrical resistivity of the film is found to be about 4.37 × 10{sup −4} Ω cm. In addition, the influence of oxygen pressure on optical properties in NZO thin films was systematically studied as well.

  19. Good Quality Factor in GdMnO3-Doped (K0.5Na0.5)NbO3 Piezoelectric Ceramics

    Science.gov (United States)

    Bucur, Raul Alin; Badea, Iuliana; Bucur, Alexandra Ioana; Novaconi, Stefan

    2016-06-01

    (1 - x)(K0.5Na0.5)NbO3 - xGdMnO3 (KNN- xGM) ferroelectric ceramics (0 ≤ x ≤ 5 mol.%) were obtained through a solid state technique. For all the studied compositions, orthorhombic perovskite crystalline structures were obtained at room temperature. GdMnO3 suppresses the grain growth and gives rather homogenous microstructures as the concentration increases. The doped ceramics exhibita good dielectric response, a "hard" ferroelectric behavior and good piezoelectric properties. An improved mechanical quality factor of 1180 and a high Curie temperature T C = 400°C, coupled with k p = 0.426, makes the composition x = 1 mol.% GdMnO3 suitable for lead-free piezoelectric materials for high-power and high-temperature applications.

  20. Half-joule output optical-parametric oscillation by using 10-mm-thick periodically poled Mg-doped congruent LiNbO3.

    Science.gov (United States)

    Ishizuki, Hideki; Taira, Takunori

    2012-08-27

    We present a next generation of large-aperture periodically poled Mg-doped LiNbO3 (PPMgLN) device with 10-mm thickness. Efficient optical parametric oscillation with 540 mJ output energy at 709 mJ pumping by 1.064 µm laser in 10 nanoseconds operation could be demonstrated using the 10-mm-thick PPMgLN with an inversion period of 32.2 µm at total conversion efficiency > 76%. We also confirmed that degradation effect of conversion-efficiency distribution by wedged-inversion structures, which is inevitable in current poling condition of the large-aperture PPMgLN, can be ignored in high-intensity operation.

  1. Broadband 1.5-μm emission of erbium-doped TeO2-WO3-Nb2O5 glass for potential WDM amplifier

    Institute of Scientific and Technical Information of China (English)

    Shiqing Xu(徐时清); Shixun Dai(戴世勋); Junjie Zhang(张军杰); Lili Hu(胡丽丽); Zhonghong Jiang(姜中宏)

    2004-01-01

    @@ Erbium-doped glass showing the wider 1.5-/μm emission band is reported in a novel oxide system TeO2-WO3-Nb2O5 and their thermal stability and optical properties such as absorption,emission spectra,cross-sections and fluorescence lifetime were investigated.Compared with other glass hosts,the gain bandwidthproperties of Er3+ in TWN glass is close to that of bismuth glasses,and larger than those of tellurite,germanatc,silicate and phosphate glasses.The broad and flat 4I13/2 → 4I15/2 emission and the largestimulated emission cross-section of Er3+ ions around 1.5 μm can be used as host material for potentialbroadband optical amplifier in the wavelength-division-multiplexing(WDM)network system.

  2. 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.

  3. Striking Doping Effects on Thermal Methane Activation Mediated by the Heteronuclear Metal Oxides [XAlO4 ](.+) (X=V, Nb, and Ta).

    Science.gov (United States)

    Wu, Xiao-Nan; Li, Jilai; Schlangen, Maria; Zhou, Shaodong; González-Navarrete, Patricio; Schwarz, Helmut

    2017-01-18

    The thermal reactivity of the heteronuclear metal-oxide cluster cations [XAlO4 ](.+) (X=V, Nb, and Ta) towards methane has been studied by using mass spectrometry in conjunction with quantum mechanical calculations. Experimentally, a hydrogen-atom transfer (HAT) from methane is mediated by all the three oxide clusters at ambient conditions. However, [VAlO4 ](.+) is unique in that this cluster directly transforms methane into formaldehyde. The absence of this reaction for the Nb and Ta analogues demonstrates a striking doping effect on the chemoselectivity in the conversion of methane. Mechanistic aspects of the two reactions have been elucidated by quantum-chemical calculations. The HAT reactivity can be attributed to the significant spin density localized at the terminal oxygen atom (Ot(.-) ) of the cluster ions, while the ionic/covalent character of the Lewis acid-base unit [X-Ob ] plays a crucial role for the generation of formaldehyde. The mechanistic insight derived from this combined experimental/computational investigation may provide guidance for a more rational design of catalysts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Phase transition and piezoelectric properties of Nd3+ doped nonstoichiometric (K,Na)NbO3-based lead free ceramics

    Science.gov (United States)

    Xing, Jie; Tan, Zhi; Jiang, Laiming; Wu, Yangjie; Yue, Yang; Chen, Qiang; Wu, Jiagang; Zhang, Wen; Xiao, Dingquan; Zhu, Jianguo

    2017-01-01

    0.968[(K0.48Na0.52)]1-3xNdxNb0.95+ySb0.05O3-0.032(Bi0.5Na0.5)ZrO3[KNNdxNb0.95+yS-BNZ] lead-free piezoelectric ceramics were prepared via conventional solid state technique for improving the piezoelectric properties. The influences of Nd3+ with excess Nb5+ on the phase structure, electrical properties, and temperature stability were investigated systematically. The rhombohedral-tetragonal phase boundary was observed in the ceramics with 0.001 ≤ x ≤ 0.004, y ≥ 0.01 at room temperature. Rietveld refinement is performed to explore the phase evolution in ceramics. There is a piezoelectric property enhancement in the ceramic with x = 0.001 y = 0.01: d33 = 414 pC/N, kp ˜ 48%, and TC ˜ 227 °C. All results suggest that KNNdxNb0.95+yS-BNZ ceramics developed in this study are expected to be suitable substitutes for lead-based ceramics.

  5. The local structure and ferromagnetism in Fe-implanted SrTiO3 single crystals

    Science.gov (United States)

    Lobacheva, O.; Chavarha, M.; Yiu, Y. M.; Sham, T. K.; Goncharova, L. V.

    2014-07-01

    We report a connection between the local structure of low-level Fe impurities and vacancies as the cause of ferromagnetic behavior observed in strontium titanate single crystals (STO), which were implanted with Fe and Si ions at different doses then annealed in oxygen. The effects of Fe doping and post-implantation annealing of STO were studied by X-ray Absorption Near Edge Structure (XANES) spectroscopy and Superconducting Quantum Interference Device magnetometry. XANES spectra for Fe and Ti K- and L-edge reveal the changes in the local environment of Fe and Ti following the implantation and annealing steps. The annealing in oxygen atmosphere partially healed implantation damages and changed the oxidation state of the implanted iron from metallic Fe0 to Fe2+/Fe3+ oxide. The STO single crystals were weak ferromagnets prior to implantation. The maximum saturation moment was obtained after our highest implantation dose of 2 × 1016 Fe atom/cm2, which could be correlated with the metallic Fe0 phases in addition to the presence of O/Ti vacancies. After recrystallization annealing, the ferromagnetic response disappears. Iron oxide phases with Fe2+ and Fe3+ corresponding to this regime were identified and confirmed by calculations using Real Space Multiple Scattering program (FEFF9).

  6. 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....... During the deposition, the LaAlO3 ablation plume is also studied, in situ, by fast photography and space-resolved optical emission spectroscopy. An interesting correlation between interfacial conductivity and kinetic energy of the Al atoms in the plume is observed: to assure conducting interfaces...

  7. Crystal Structure, Piezoelectric and Dielectric Properties of (Li, Ce)4+, Nb5+ and Mn2+ Co-doped CaBi4Ti4O15 High-Temperature Ceramics

    Science.gov (United States)

    Xin, Deqiong; Chen, Qiang; Wu, Jiagang; Bao, Shaoming; Zhang, Wen; Xiao, Dingquan; Zhu, Jianguo

    2016-07-01

    Bismuth-layered structured ceramics Ca0.85(Li,Ce)0.075Bi4Ti4- x Nb x O15-0.01MnCO3 were prepared by the conventional solid-state reaction method. The evolution of microstructure and corresponding electrical properties were studied. All the samples presented a single bismuth layered-structural phase with m = 4, indicating that (Li, Ce)4+, Nb5+ and Mn2+ adequately enter into the pseudo-perovskite structure and form solid solutions. It was found that Ca0.85(Li,Ce)0.075Bi4Ti3.98Nb0.02O15-0.01MnCO3 (CBTLCM-0.02Nb) ceramics possess the optimum electrical properties. The piezoelectric coefficient d 33, dielectric constant ɛ r, loss tan δ, planar electromechanical coupling factor k p and Curie-temperature T C of CBTLCM-0.02Nb ceramics were found to be ˜19.6 pC/N, 160, 0.16%, 8.1% and 767°C, respectively. Furthermore, the thermal depoling behavior demonstrates that the d 33 value of x = 0.02 content remains at 16.8 pC/N after annealing at 500°C. These results suggest that the (Li, Ce)4+-, Nb5+- and Mn2+-doped CBT-based ceramics are promising candidates for high-temperature piezoelectric applications.

  8. Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

    Science.gov (United States)

    Diao, Shuyan; Yao, Jianquan; Zheng, Yi; Geng, Youfu; Tan, Xiaoling; Liu, Qiang; Xu, Longhao

    2006-09-01

    A widely and continuously tunable optical parametric generator (OPG) pumped by a 1064-nm acousto-optically Q-switched diode-end-pumped Nd:YAG laser based on MgO-doped periodically poled LiNbO3 crystal with a multigrating structure (29.2-30.4 micron) is reported. A broad continuous signal spectrum of 1513-1700 nm is obtained by changing the crystal grating periods from 29.2 to 30.4 micron and by tuning the crystal temperature from 30 to 180 Celsius degrees simultaneously. When the average pump power is 1.82 W with pulse duration of about 70 ns operating at a repetition rate of 10 kHz, the maximum signal output power of the periodically poled MgO-doped lithium niobate (PPMgLN) OPG is about 210 mW corresponding to the idler and total powers of 118.4 and 328.4 mW respectively.

  9. Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

    Institute of Scientific and Technical Information of China (English)

    Shuyan Diao; Jianquan Yao; Yi Zheng; Youfu Geng; Xiaoling Tan; Qiang Liu; Longhao Xu

    2006-01-01

    @@ A widely and continuously tunable optical parametric generator (OPG) pumped by a 1064-nm acoustooptically Q-switched diode-end-pumped Nd:YAG laser based on MgO-doped periodically poled LiNbO3 crystal with a multigrating structure (29.2-30.4 μm) is reported.A broad continuous signal spectrum of 1513-1700 nm is obtained by changing the crystal grating periods from 29.2 to 30.4μm and by tuning the crystal temperature from 30 to 180 ℃ simultaneously.When the average pump power is 1.82 W with pulse duration of about 70 ns operating at a repetition rate of 10 kHz,the maximum signal output power of the periodically poled MgO-doped lithium niobate (PPMgLN) OPG is about 210 mW corresponding to the idler and total powers of 118.4 and 328.4 mW respectively.

  10. Monte Carlo simulations of backscattering process in dislocation-containing SrTiO3 single crystal

    Science.gov (United States)

    Jozwik, P.; Sathish, N.; Nowicki, L.; Jagielski, J.; Turos, A.; Kovarik, L.; Arey, B.

    2014-05-01

    Studies of defects formation in crystals are of obvious importance in electronics, nuclear engineering and other disciplines where materials are exposed to different forms of irradiation. Rutherford Backscattering/Channeling (RBS/C) and Monte Carlo (MC) simulations are the most convenient tool for this purpose, as they allow one to determine several features of lattice defects: their type, concentration and damage accumulation kinetic. On the other hand various irradiation conditions can be efficiently modeled by ion irradiation method without leading to the radioactivity of the sample. Combination of ion irradiation with channeling experiment and MC simulations appears thus as a most versatile method in studies of radiation damage in materials. The paper presents the results on such a study performed on SrTiO3 (STO) single crystals irradiated with 320 keV Ar ions. The samples were analyzed also by using HRTEM as a complementary method which enables the measurement of geometrical parameters of crystal lattice deformation in the vicinity of dislocations. Once the parameters and their variations within the distance of several lattice constants from the dislocation core are known, they may be used in MC simulations for the quantitative determination of dislocation depth distribution profiles. The final outcome of the deconvolution procedure are cross-sections values calculated for two types of defects observed (RDA and dislocations).

  11. Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

    Science.gov (United States)

    Santander-Syro, A. F.; Fortuna, F.; Bareille, C.; Rödel, T. C.; Landolt, G.; Plumb, N. C.; Dil, J. H.; Radović, M.

    2014-12-01

    Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides exhibit a range of properties, including tunable insulator-superconductor-metal transitions, large magnetoresistance, coexisting ferromagnetism and superconductivity, and a spin splitting of a few meV (refs , ). Strontium titanate (SrTiO3), the cornerstone of such oxide-based electronics, is a transparent, non-magnetic, wide-bandgap insulator in the bulk, and has recently been found to host a surface 2DEG (refs , , , ). The most strongly confined carriers within this 2DEG comprise two subbands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces. Using spin- and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these subbands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated. Moreover, in contrast to a simple Rashba system, the spin-polarized subbands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.

  12. Interplay between Superconductivity and Ferromagnetism at the LaAlO3/SrTiO3 Interface

    Science.gov (United States)

    Mehta, Manan

    As we approach the limit of minimum feature size in silicon based technology, there. is a need to move to novel, low-dimensional, multi-functional materials which can power. the future generations of computers. Many complex oxide materials show a rich variety. of multi-functional properties and are thought to be viable candidates for future comput-. ing devices. We study here one such complex oxide heterostructure, the LaAlO3 /SrTiO3. (LAO/STO) interface, which has been shown to host a two dimensional electron gas. (2DEG). Physical phenomena that have been observed at the interface include super-. conductivity, magnetism, a metal-to-insulator transition, and a gate voltage tuned two. dimensional superconductor-to-insulator transition (SIT). This thesis presents evidence. for the coexistence of the two conventionally competing phenomena of superconductivity. and ferromagnetism at the interface. It further explores the interplay between the two. orders through electrical transport measurements, which results in a novel manifestation. of charge-vortex duality between the superconducting and insulating states as the system. is tuned through the gate voltage tuned SIT. A phenomenological model of the system. is presented which helps explain the observed transport behaviour. Finally, the magnetic. field tuned SIT at this interface is also presented along with a scaling analysis of the. magnetoresistance.

  13. Accurate Modeling of the Cubic and Antiferrodistortive Phases of SrTiO3 with Screened Hybrid Density Functional Theory

    CERN Document Server

    El-Mellouhi, Fadwa; Lucero, Melissa J; Scuseria, Gustavo E

    2011-01-01

    We have calculated the properties of SrTiO3 (STO) using a wide array of density functionals ranging from standard semi-local functionals to modern range-separated hybrids, combined with several basis sets of varying size/quality. We show how these combination's predictive ability varies signi?cantly, both for STO's cubic and antiferrodistortive (AFD) phases, with the greatest variation in functional/basis set e?cacy seen in modeling the AFD phase. The screened hybrid functionals we utilized predict the structural properties of both phases in very good agreement with experiment, especially if used with large (but still computationally tractable) basis sets. The most accurate results presented in this study, namely those from HSE06/modi?ed-def2-TZVP, stand as the most accurate modeling of STO to date when compared to the literature; these results agree well with experimental structural and electronic properties as well as providing insight into the band structure alteration during the phase transition.

  14. Giant conductivity switching of LaAlO3/SrTiO3 heterointerfaces governed by surface protonation

    Science.gov (United States)

    Brown, Keith A.; He, Shu; Eichelsdoerfer, Daniel J.; Huang, Mengchen; Levy, Ishan; Lee, Hyungwoo; Ryu, Sangwoo; Irvin, Patrick; Mendez-Arroyo, Jose; Eom, Chang-Beom; Mirkin, Chad A.; Levy, Jeremy

    2016-02-01

    Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. Despite intense interest, many basic questions remain about the mechanisms that give rise to interfacial conductivity and the role of surface chemistry in dictating these properties. Here we demonstrate a fully reversible >4 order of magnitude conductance change at LaAlO3/SrTiO3 (LAO/STO) interfaces, regulated by LAO surface protonation. Nominally conductive interfaces are rendered insulating by solvent immersion, which deprotonates the hydroxylated LAO surface; interface conductivity is restored by exposure to light, which induces reprotonation via photocatalytic oxidation of adsorbed water. The proposed mechanisms are supported by a coordinated series of electrical measurements, optical/solvent exposures, and X-ray photoelectron spectroscopy. This intimate connection between LAO surface chemistry and LAO/STO interface physics bears far-reaching implications for reconfigurable oxide nanoelectronics and raises the possibility of novel applications in which electronic properties of these materials can be locally tuned using synthetic chemistry.

  15. Depth dependence of strain, mosaicity and sharp component in the critical scattering of SrTiO3

    Science.gov (United States)

    Rütt, U.; Diederichs, A.; Schneider, J. R.; Shirane, G.

    1997-08-01

    The sharp component observed in the critical scattering above the cubic-to-tetragonal phase transition in SrTiO3 is now generally considered as a surface-related phenomenon. In the present paper, for the first time, the structural difference between the bulk and a skin layer of a highly perfect crystal has been shown quantitatively by diffraction methods. High-resolution measurements have been performed with highly penetrating 121 keV synchrotron radiation X-rays. The lattice parameter d, its fluctuations Δd/d, the crystal mosaicity and the critical scattering were found to be depth dependent. The two-length-scale behaviour in the critical fluctuations is confined to a skin layer approximately 100 μm thick and related to an increase in strain. Approaching the crystal surface the lattice parameter decreases by 6.2·10-5 Å, Δd/d increases from the bulk value of 5.2·10-5 to 13·10-5, the mosaicity increases from 1.0 to 8.2 seconds of arc. In addition the critical temperature determined from the temperature dependence of the 1/2(511) reflection at the surface and 150 μm below, is smaller than the bulk value by 1.7 and 2.4 K, respectively.

  16. Two-Dimensional Electron Gas at SrTiO3-Based Oxide Heterostructures via Atomic Layer Deposition

    Directory of Open Access Journals (Sweden)

    Sang Woon Lee

    2016-01-01

    Full Text Available Two-dimensional electron gas (2DEG at an oxide interface has been attracting considerable attention for physics research and nanoelectronic applications. Early studies reported the formation of 2DEG at semiconductor interfaces (e.g., AlGaAs/GaAs heterostructures with interesting electrical properties such as high electron mobility. Besides 2DEG formation at semiconductor junctions, 2DEG was realized at the interface of an oxide heterostructure such as the LaAlO3/SrTiO3 (LAO/STO heterojunction. The origin of 2DEG was attributed to the well-known “polar catastrophe” mechanism in oxide heterostructures, which consist of an epitaxial LAO layer on a single crystalline STO substrate among proposed mechanisms. Recently, it was reported that the creation of 2DEG was achieved using the atomic layer deposition (ALD technique, which opens new functionality of ALD in emerging nanoelectronics. This review is focused on the origin of 2DEG at oxide heterostructures using the ALD process. In particular, it addresses the origin of 2DEG at oxide interfaces based on an alternative mechanism (i.e., oxygen vacancies.

  17. Tailoring the Two Dimensional Electron Gas at Polar ABO3/SrTiO3 Interfaces for Oxide Electronics

    Science.gov (United States)

    Li, Changjian; Liu, Zhiqi; Lü, Weiming; Wang, Xiao Renshaw; Annadi, Anil; Huang, Zhen; Zeng, Shengwei; Ariando; Venkatesan, T.

    2015-08-01

    The 2D electron gas at the polar/non-polar oxide interface has become an important platform for several novel oxide electronic devices. In this paper, the transport properties of a wide range of polar perovskite oxide ABO3/SrTiO3 (STO) interfaces, where ABO3 includes LaAlO3, PrAlO3, NdAlO3, NdGaO3 and LaGaO3 in both crystalline and amorphous forms, were investigated. A robust 4 unit cell (uc) critical thickness for metal insulator transition was observed for crystalline polar layer/STO interface while the critical thickness for amorphous ones was strongly dependent on the B site atom and its oxygen affinity. For the crystalline interfaces, a sharp transition to the metallic state (i.e. polarization catastrophe induced 2D electron gas only) occurs at a growth temperature of 515 °C which corresponds to a critical relative crystallinity of ~70 ± 10% of the LaAlO3 overlayer. This temperature is generally lower than the metal silicide formation temperature and thus offers a route to integrate oxide heterojunction based devices on silicon.

  18. Anomalous enhancement of the sheet carrier density beyond the classic limit on a SrTiO3 surface

    Science.gov (United States)

    Kumar, Neeraj; Kitoh, Ai; Inoue, Isao H.

    2016-05-01

    Electrostatic carrier accumulation on an insulating (100) surface of SrTiO3 by fabricating a field effect transistor with Parylene-C (6 nm)/HfO2 (20 nm) bilayer gate insulator has revealed a mystifying phenomenon: sheet carrier density is about 10 times as large as ( is the sheet capacitance of the gate insulator, VG is the gate voltage, and e is the elementary charge). The channel is so clean to exhibit small subthreshod swing of 170 mV/decade and large mobility of 11 cm2/Vs for of 1 × 1014 cm‑2 at room temperature. Since does not depend on either VG nor time duration, beyond is solely ascribed to negative charge compressibility of the carriers, which was in general considered as due to exchange interactions among electrons in the small limit. However, the observed is too large to be naively understood by the framework. Alternative ideas are proposed in this work.

  19. Oxygenation Dependence of the Resistance Upturn in LaAlO3 /SrTiO3 Heterostructures

    Science.gov (United States)

    Zhang, H.; Majlan, K. A.; Ngai, J. H.; McMahon, C.; Hawthorn, D. G.; Wei, J. Y. T.

    Among the phenomena exhibited by LaAlO3/SrTiO3 (LAO/STO) heterostructures, the appearance of a low-temperature resistance upturn has attracted much recent debate. This phenomenon has been observed to co-occur with both nonlinear Hall effect and anisotropic magnetoresistance, and attributed to either Kondo effect, multiband conduction, or localization. It is primarily seen in samples grown by pulsed laser deposition, and is sensitive to film thickness, growth condition and electrostatic gating, all of which could affect the oxygen content. In this work, we study the effect of post-growth oxygenation on the resistance upturn in samples grown by molecular beam epitaxy, and how the Hall conductance and magnetoresistance are related to the occurrence of the upturn. X-ray photoelectron spectroscopy is used to monitor the valence states of Ti ions, in an effort to correlate them with the conduction and magnetic properties. Our results are analyzed in terms of oxygen vacancies in the presence of polar charge transfer, and the effect of these vacancies on the resistance upturn in LAO/STO heterostructures Work supported by NSERC, CFI/OIT, and the Canadian Institute for Advanced Research.

  20. Perovskite oxide SrTiO3 as an efficient electron transporter for hybrid perovskite solar cells

    KAUST Repository

    Bera, Ashok

    2014-12-11

    In this work, we explored perovskite oxide SrTiO3 (STO) for the first time as the electron-transporting layer in organolead trihalide perovskite solar cells. The steady-state photoluminescence (PL) quenching and transient absorption experiments revealed efficient photoelectron transfer from CH3NH3PbI3-xClx to STO. Perovskite solar cells with meso-STO exhibit an open circuit voltage of 1.01 V, which is 25% higher than the value of 0.81 V achieved in the control device with the conventional meso-TiO2. In addition, an increase of 17% in the fill factor was achieved by tailoring the thickness of the meso-STO layer. We found that the application of STO leads to uniform perovskite layers with large grains and complete surface coverage, leading to a high shunt resistance and improved performance. These findings suggest STO as a competitive candidate as electron transport material in organometal perovskite solar cells.

  1. Conductivity of the two-dimensional electron gas at LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Kirichenko, E. V.; Stephanovich, V. A.; Dugaev, V. K.

    2017-02-01

    We propose an analytical theory of metallic conductivity in the two-dimensional (2D) LaAlO3/SrTiO3 (LAO/STO) interface. For that we consider the electron-phonon interaction at the interface. The electronic part is taken from our previous work [Phys. Chem. Chem. Phys. 18, 2104 (2016), 10.1039/C5CP06627A], considering the conditions for the interfacial charge carrier (electron or hole) to become itinerant. The second ingredient deals with the atomic oscillations localized near the interface and decaying rapidly at its both sides, which can be regarded as 2D acoustic phonons. The dispersion of such phonons depends on the characteristics of phonon spectra of LAO and STO. Calculating the corresponding scattering rate by Fermi's golden rule, we show that the resulting resistivity (i.e., inverse conductivity) has typical metallic character, growing linearly with temperature and tending to zero (without defects forming so-called residual resistivity) at T →0 . The results of our calculations are in agreement with available experimental data.

  2. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum.

    Science.gov (United States)

    Lee, Ho Nyung; Ambrose Seo, Sung S; Choi, Woo Seok; Rouleau, Christopher M

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well.

  3. Temperature-dependent dielectric function of bulk SrTiO3: Urbach tail, band edges, and excitonic effects

    Science.gov (United States)

    Gogoi, Pranjal Kumar; Schmidt, Daniel

    2016-02-01

    We report the temperature-dependent complex dielectric function of pristine bulk SrTiO3 between 4.2 and 300 K within the energy range of 0.6-6.5 eV determined by spectroscopic ellipsometry. Fundamental indirect and direct band-gap energies have been extracted and are discussed with regard to existing state-of-the-art theoretical calculations. Furthermore, the dielectric function around the fundamental direct gap is analyzed by considering excitonic states. The excitonic effects, including the Coulomb enhancement of the continuum, are characterized using an extension of the Elliott's formula considering both the real and imaginary parts of the dielectric function. The Urbach tail below the indirect edge shows an unconventional temperature-dependent behavior correlated to the microstructural changes near the structural phase transition around 105 K from the low-temperature tetragonal phase to the cubic phase. The temperature-dependent characterization reveals that the fundamental indirect edge as well as the Urbach tail are affected conspicuously by the structural phase transition while the fundamental direct edge is not. Moreover, the indirect edge follows Varshni's rule only in the cubic phase and the direct edge exhibits an anomalous linear increase with increasing temperature.

  4. Contributions to the dielectric losses of textured SrTiO3 thin films with Pt electrodes

    Science.gov (United States)

    Lu, Jiwei; Schmidt, Steffen; Ok, Young-Woo; Keane, Sean P.; Stemmer, Susanne

    2005-09-01

    The factors controlling low-frequency (1 MHz) dielectric losses of textured SrTiO3 thin films deposited by radio-frequency magnetron sputtering on platinized sapphire substrates were investigated. In particular, the influence of film texture, phase transformations, applied bias field, temperature, and annealing atmospheres was studied. Films that were (111) textured showed a phase transformation at ~150 K, whereas films that were predominantly (110) oriented did not exhibit a phase transformation in the measured temperature range (100-300 K). Two major contributions to the dielectric losses were identified: a low-temperature loss increase for the (111) oriented film, which could be suppressed by an applied bias field, and a loss peak at ~250 K (at 1 MHz), which was strongly frequency-dependent and likely associated with a relaxing defect. The low-temperature loss mode was related to the appearance of a phase transformation and contributed to the dielectric losses even at temperatures that were more than 100 K above the phase transformation. In contrast to the leakage properties of the films, which were strongly dependent on annealing atmospheres, annealing under reducing conditions had no significant influence on any of the observed loss modes. Possible origins of the different loss contributions were discussed.

  5. Anisotropic multicarrier transport at the (111) LaAlO3/SrTiO3 interface

    Science.gov (United States)

    Davis, S.; Chandrasekhar, V.; Huang, Z.; Han, K.; Ariando, Venkatesan, T.

    2017-01-01

    The conducting gas that forms at the interface between LaAlO3 and SrTiO3 has proven to be a fertile playground for a wide variety of physical phenomena. The bulk of previous research has focused on the (001) and (110) crystal orientations. Here we report detailed measurements of the low-temperature electrical properties of (111) LAO/STO interface samples. We find that the low-temperature electrical transport properties are highly anisotropic in that they differ significantly along two mutually orthogonal crystal orientations at the interface. While anisotropy in the resistivity has been reported in some (001) samples and in (110) samples, the anisotropy in the (111) samples reported here is much stronger and also manifests itself in the Hall coefficient as well as the capacitance. In addition, the anisotropy is not present at room temperature and at liquid nitrogen temperatures, but only at liquid helium temperatures and below. The anisotropy is accentuated by exposure to ultraviolet light, which disproportionately affects transport along one surface crystal direction. Furthermore, analysis of the low-temperature Hall coefficient and the capacitance as a function of back gate voltage indicates that in addition to electrons, holes contribute to the electrical transport.

  6. High-sensitivity photovoltage based on the interfacial photoelectric effect in the SrTiO3-δ/Si heterojunction

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A high sensitivity photovoltaic effect has been observed in a heterojunction composed of n-type wide bandgap oxide SrTiO 3-δ and p-type Si fabricated by laser molecular beam epitaxy.The responsivity of open-circuit photovoltage can reach 10 4 V/W without any amplification under zero bias for the wavelength range from visible to near infrared light in nW-μW order.We attribute the high performance of the photovoltage responsivity to the interfacial photoelectric effects in the SrTiO 3-δ /Si heterojunction.From the experimental results,some ideas can be generalized to improve photovoltaic efficiency and develop high sensitivity photodetectors with wide bandgap oxide materials and Si.

  7. Strain effects on the spin polarized electron gas in ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures

    KAUST Repository

    Nazir, Safdar

    2013-04-11

    The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.

  8. High resistance modulation by the electric field based on La0.9Sr0.1MnO3/SrTiO3/Si structure

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    A field-effect configuration based on La0.9Sr0.1MnO3/SrTiO3/Si structure is fabricated on Si substrate by laser molecular-beam epitaxy. The resistance modulation by electric field of the La0.9Sr0.1MnO3/SrTiO3/Si structure is investigated in detail. An evident resistance modulation effect is observed at 80 K. The channel resistance modulation by field effect reaches 1.4×107% and 2.6×106% when VDS are -2 and -6.5 V, respectively. The ON/OFF ratio of approximately 4000 is obtained. The present results are worthy of further investigations for potential applications of resistance modulation by electrostatic field in the heterostructures consisting of perovskite oxides and Si.

  9. 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.

  10. Magneto-Optical Study of Defect Induced Sharp Photoluminescence in LaAlO3 and SrTiO3

    Science.gov (United States)

    Sarkar, Soumya; Saha, Surajit; Motapothula, M. R.; Patra, Abhijeet; Cao, Bing-Chen; Prakash, Saurav; Cong, Chun Xiao; Mathew, Sinu; Ghosh, Siddhartha; Yu, Ting; Venkatesan, T.

    2016-01-01

    Strongly correlated electronic systems such as Transition Metal Oxides often possess various mid-gap states originating from intrinsic defects in these materials. In this paper, we investigate an extremely sharp Photoluminescence (PL) transition originating from such defect states in two widely used perovskites, LaAlO3 and SrTiO3. A detailed study of the PL as a function of temperature and magnetic field has been conducted to understand the behavior and origin of the transition involved. The temperature dependence of the PL peak position for SrTiO3 is observed to be opposite to that in LaAlO3. Our results reveal the presence of a spin/orbital character in these transitions which is evident from the splitting of these defect energy levels under a high magnetic field. These PL transitions have the potential for enabling non-contact thermal and field sensors. PMID:27619076

  11. Unit-Cell by Unit-Cell Homoepitaxial Growth Using Atomically Flat SrTiO3(001) Substrates and Pulsed Laser Deposition

    Institute of Scientific and Technical Information of China (English)

    FEI Yi-Yan; WANG Xu; LU Hui-Bin; YANG Guo-Zhen; ZHU Xiang-Dong

    2005-01-01

    @@ Using a combination of chemical etching and thermal annealing methods, we have obtained atomically flat TiO2-terminated SrTiO3 (001) with large terraces.The average width of the terrace is only determined by miscut angles.When we continuously grow tens of SrTiO3 monolayers on such a surface under pulsed laser ablation deposition condition at 621℃, the growth proceeds in a layer-by-layer mode characterized by un-damped oscillations of the specular RHEED intensity.After the growth of 180 monolayers, the surface morphology is restored to the pre-growth condition with similarly large terraces after annealing in vacuum for only 30 min, indicating efficient mass transfer on TiO2-terminated terraces.

  12. Effect of the change in the interface structure of Pd(100)/SrTiO3 for quantum-well induced ferromagnetism

    Science.gov (United States)

    Sakuragi, Shunsuke; Ogawa, Tomoyuki; Sato, Tetsuya

    2017-02-01

    Measurements of temperature dependent magnetization of Pd(100) ultrathin films on SrTiO3(100) substrates which shows quantum-well induced ferromagnetism were performed. We observed the jump in magnetization of Pd(100) due to the structural phase transition of SrTiO3, and then, the disappearance of ferromagnetism after temperature-cycle repetition. X-ray reflectivity measurement revealed that the density of a few layers in the Pd film decreased near the Pd/SrTiO3 interface after temperature cycles. This suggests that the structural change affects the quantum-well induced ferromagnetism, and lowering of the crystallinity of Pd at the interface has a negative effect on quantum-well induced ferromagnetism of Pd(100) ultrathin films.

  13. Lattice dynamical analogies and differences between SrTiO3 and EuTiO3 revealed by phonon-dispersion relations and double-well potentials

    Science.gov (United States)

    Bettis, Jerry L.; Whangbo, Myung-Hwan; Köhler, Jürgen; Bussmann-Holder, Annette; Bishop, A. R.

    2011-11-01

    A comparative analysis of the structural phase transitions of EuTiO3 and SrTiO3 (at TS = 282 and 105 K, respectively) is made on the basis of phonon-dispersion and density functional calculations. The phase transition of EuTiO3 is predicted to arise from the softening of a transverse acoustic zone boundary mode caused by the rotations of the TiO6 octahedra, as also found for the phase transition of SrTiO3. Although the temperature dependence of the soft mode is similar in both compounds, their elastic properties differ drastically because of a large difference in the double-well potentials associated with the soft zone boundary acoustic mode.

  14. Revisiting the fascinating properties of EuTiO3 and its mixed crystals with SrTiO3: Possible candidates for novel functionalities

    Science.gov (United States)

    Bussmann-Holder, Annette; Köhler, Jürgen

    2015-09-01

    The research in perovskite oxides is ever increasing since their discovery in 1945. The number of compounds with this rather simple structure is growing continuously since then and fascinating properties ranging from magnetic via dielectric and superconducting have been reported for them. While an extreme research activity has been devoted to SrTiO3 from its discovery on, its analog EuTiO3 has attracted rather little interest until recently. In this review we concentrate on the recent results from studies of this perovskite and its mixed crystals with SrTiO3 and demonstrate that novel interesting properties are related to it. Specifically we provide evidence for the existence of hybrid-paramagnon-phonon coupling at elevated temperatures and its manifestations in bulk sensitive experiments. In addition, the phase diagram of the mixed crystal series is presented where pressure and temperature effects are included.

  15. Effects of BaTiO3 and SrTiO3 as the buffer layers of epitaxial BiFeO3 thin films

    Science.gov (United States)

    Feng, Yu; Wang, Can; Tian, ShiLu; Zhou, Yong; Ge, Chen; Guo, HaiZhong; He, Meng; Jin, KuiJuan; Yang, GuoZhen

    2017-06-01

    BiFeO3 (BFO) thin films with BaTiO3 (BTO) or SrTiO3 (STO) as buffer layer were epitaxially grown on SrRuO3-covered SrTiO3 substrates. X-ray diffraction measurements show that the BTO buffer causes tensile strain in the BFO films, whereas the STO buffer causes compressive strain. Different ferroelectric domain structures caused by these two strain statuses are revealed by piezoelectric force microscopy. Electrical and magnetical measurements show that the tensile-strained BFO/BTO samples have reduced leakage current and large ferroelectric polarization and magnetization, compared with compressively strained BFO/STO. These results demonstrate that the electrical and magnetical properties of BFO thin films can be artificially modified by using a buffer layer.

  16. Influence of oxygen pressure and aging on LaAlO3 films grown by pulsed laser deposition on SrTiO3 substrates

    KAUST Repository

    Park, Jihwey

    2014-02-24

    The crystal structures of LaAlO3 films grown by pulsed laser deposition on SrTiO3 substrates at oxygen pressure of 10−3 millibars or 10−5 millibars, where kinetics of ablated species hardly depend on oxygen background pressure, are compared. Our results show that the interface between LaAlO3 and SrTiO3 is sharper when the oxygen pressure is lower. Over time, the formation of various crystalline phases is observed while the crystalline thickness of the LaAlO3 layer remains unchanged. X-ray scattering as well as atomic force microscopy measurements indicate three-dimensional growth of such phases, which appear to be fed from an amorphous capping layer present in as-grown samples.

  17. An Investigation into W or Nb or ZnFe2O4 Doped Titania Nanocomposites Deposited from Blended Powder Targets for UV/Visible Photocatalysis

    Directory of Open Access Journals (Sweden)

    Vladimir Vishnyakov

    2013-08-01

    Full Text Available The photocatalytic behavior of titania coatings is largely determined by their crystalline structure. Depending on deposition conditions, though, titania may form amorphous, brookite, anatase or rutile structures, with anatase or anatase/rutile mixed phase structures showing the highest levels of activity. Anatase is activated by UV light and, consequently, there is a great deal of interest in doping titania films to both increase activity and extend it into the visible range. In this study, titania and doped titania coatings have been deposited from blended oxide powder targets. This highly versatile and economical technique allows dopant levels to be readily varied. Using this technique, titania coatings doped with W, Nb and ZnFe2O4 have been deposited onto glass substrates by pulsed magnetron sputtering. The as-deposited coatings were analyzed by scanning electron microscopy (SEM, energy dispersive X-ray spectroscopy (EDX and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analyzed. Structural transformation of the titania coatings was initiated in the 500–600 °C range, with the coatings annealed at 700 °C having predominantly anatase structures. The photocatalytic activity of the coatings was assessed through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. It was found that, after annealing, coatings with photo-active surfaces were produced and that activity varied with dopant content. Activity levels under fluorescent light irradiation were up to 60% of the activity measured under UV irradiation.

  18. A Universal Critical Density Underlying the Physics of Electrons at the LaAlO3/SrTiO3 Interface

    OpenAIRE

    Joshua, Arjun; Pecker, S.; Ruhman, J.; Altman, E; Ilani, S.

    2011-01-01

    The two-dimensional electron system formed at the interface between the insulating oxides LaAlO3 and SrTiO3 exhibits ferromagnetism, superconductivity, and a wide range of unique magnetotransport properties. A key challenge is to find a unified microscopic mechanism that underlies these emergent phenomena. Here we show that a universal Lifshitz transition between d-orbitals lies at the core of the observed transport phenomena in this system. Our measurements find a critical electronic density...

  19. Very High Surface Area Mesoporous Thin Films of SrTiO3 Grown by Pulsed Laser Deposition and Application to Efficient Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Sangle, Abhijeet L; Singh, Simrjit; Jian, Jie; Bajpe, Sneha R; Wang, Haiyan; Khare, Neeraj; MacManus-Driscoll, Judith L

    2016-12-14

    Very high surface area, self-assembled, highly crystalline mesoporous SrTiO3 (STO) thin films were developed for photoelectrochemical water splitting. Much improved performance of these mesoporous films compared to planar STO thin films and any other form of STO such as single crystal samples and nanostructures was demonstrated. The high performance resulted from very large surface area films and optimization of carrier concentration.

  20. Insight into synergistically enhanced adsorption and visible light photocatalytic performance of Z-scheme heterojunction of SrTiO3(La,Cr)-decorated WO3 nanosheets

    Science.gov (United States)

    Liu, Xin; Jiang, Junzhe; Jia, Yushuai; Qiu, Jinmin; Xia, Tonglin; Zhang, Yuhong; Li, Yuqin; Chen, Xiangshu

    2017-08-01

    The efficient treatment of dye wastewater has been a hot topic of environment field. The integration of adsorption and photocatalytic degradation via fabrication of bi-component heterojunction photocatalyst is considered as a facile and effective strategy to enhance the dye elimination efficiency. In this report, a Z-scheme heterojunction material, SrTiO3(La,Cr)/WO3 with bifunction of adsorption and photocatalysis was successfully synthesized for efficient removal of methylene blue (MB) under visible light irradiation. The morphology and microstructure characterization demonstrates that the SrTiO3(La,Cr) nanoparticles are uniformly decorated on the WO3 nanosheets, forming an intimate heterojunction interface. MB degradation results indicate that the removal efficiency by the synergistic adsorption-photocatalysis process is greatly improved compared to pure WO3 and SrTiO3(La,Cr) with the adsorption and photocatalytic activity closely related to the composition of the material. The possible mechanism for the enhanced photocatalytic activity could be ascribed to the formation of a Z-scheme heterojunction system based on active species trapping experiments. Furthermore, the investigations of adsorption kinetics and isotherm show that the adsorption process follows pseudo-second-order kinetic model and Langmuir isotherm, respectively. Due to the synergistic advantages of negative zeta potential, large surface area and accelerated separation of photogenerated carriers driven by Z-scheme heterojunction, SrTiO3(La,Cr)/WO3 exhibits excellent adsorption-photocatalytic performance and stability on MB removal, which could be potentially used for practical wastewater treatment.