Home About us Contact
|
Home About us Contact | ||
|
|
||
Oxygen Vacancies (oxygen + vacancy)
Terms modified by Oxygen Vacancies Selected AbstractsIncreasing the Number of Oxygen Vacancies on TiO2 by Doping with Iron Increases the Activity of Supported Gold for CO OxidationCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2007Silvio Carrettin Dr. Abstract The addition of iron to high-area TiO2 (Degussa P25, a mixture of anatase and rutile) increases the number of oxygen defect sites that react with O2 to form peroxide and superoxide species. In the presence of gold nanoclusters on the TiO2 surface, the superoxide species become highly reactive, and the activity of the supported gold catalyst for CO oxidation is approximately twice that of the most active comparable catalysts described in the literature. Images of the catalyst obtained by scanning transmission electron microscopy combined with spectra of the catalyst measured in the working state (Raman, extended X-ray absorption fine structure, and X-ray absorption near-edge structure) indicate strong interactions of gold with the support and the presence of iron near the interfaces between the gold clusters and the TiO2 support. The high activity of the catalysts is attributed to the presence of defects in these sites that activate oxygen. [source] Optical properties of ZnO nanotubesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2010Hongju Zhai Abstract Tubular ZnO nanostructures have been obtained via a hydrothermal method at low temperature (90 °C) without any catalysts or templates. The XRD measurement reveals that the tubes are single crystals with hexagonal wurtzite structure. SEM shows that the diameters of ZnO nanotubes ranged from 400 to 550 nm. The Raman and PL spectra indicate that oxygen vacancies or Zn interstitials are responsible for the green emission in the ZnO nanotubes. A possible growth mechanism on the formation of crystalline ZnO nanotubes has been presented. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Role of oxygen vacancies in the coloration of 0.65Pb(Mg1/3Nb2/3)O3 -0.35PbTiO3 single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007Zhiguo Xia Abstract The coloration and oxygen vacancies in 0.65Pb(Mg1/3Nb2/3)O3 -0.35PbTiO3 (PMN-PT(65/35)) (starting composition) single crystals grown by a so-called modified Bridgman technique were investigated in this paper. Light yellow and dark brown colored crystals were generally observed for the typical as-grown PMN-PT(65/35) single crystals. X-ray diffraction results demonstrated that they were both of pure perovskite structure, but good electric properties were only obtained for the light yellow crystal. X-ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of its components. The O 1s photoelectron spectra of the dark brown colored crystals located at the higher binding energy side, which meant the existence of the more oxygen vacancies. It accordingly led to the formation of the low valence cations associated with the coloration of the crystals, which is also testified by the obtained X-ray photoelectron spectra of Ti and Nb. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Morphological, structural and optical study of quasi-1D SnO2 nanowires and nanobeltsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005D. Calestani Abstract 0.1,0.3 mm thick entanglements of quasi-one-dimensional semiconducting Tin dioxide nanocrystals, in form of nanowires and nanobelts, are successfully grown by low cost Chemical Vapour Deposition directly on large area (100 mm2) Al2O3, SiO2 and Si substrates. Their lateral size ranges from 50 to 700 nm and their length can achieve several hundreds of micrometers. Transmission Electron Microscopy reveals either the nanowires and the nanobelts grow in the tetragonal Rutile structure. Diffraction contrast analyses and selected area diffraction investigations show the nanowires are single crystals without defects while the nanobelts sometimes present twins inside. An almost cylindrical shape and an average diameter of about 30,50 nm for the smallest nanowires is reported. X-ray diffraction investigations exclude the presence of spurious phases. A broad band structured in two emissions peaked at about 450 nm and 560 nm is revealed by large area Cathotoluminescence, while single nanocrystal spectroscopy shows that the reduction of the lateral dimension of the nanobelts from 1000 nm to 50 nm blue-shifts the main emission band at 560 nm of about 40 nm (at room temperature). These preliminary results suggest a possible role of oxygen vacancies and of the surface/volume ratio on the origin and the blue shift of Cathodoluminescence spectra. The near band edge emission, typical of bulk tin dioxide (,320 nm), is not found in nanobelts narrower than 1000 nm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of the Defects in Sintered SnO2 by High-Resolution Transmission Electron Microscopy and CathodoluminescenceEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2007David Maestre Abstract The defect structure of sintered SnO2 was investigated by high-resolution transmission electron microscopy (HRTEM), cathodoluminescence (CL), and electrical measurements. HRTEM shows the presence of the SnO phase in the sintered samples as well as twinning, stacking faults, and disordered intergrowths. The sintered samples annealed under an oxygen atmosphere show changes in the defect structure and in the CL spectra. In particular, the intensity of a CL band at 1.94 eV, related to oxygen vacancies, decreased as the electrical resistivity increased. The results are discussed by considering the presence of stoichiometric defects such as oxygen vacancies and Sn interstitials in the final structure and their evolution during the annealing process under an oxygen atmosphere. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Defect-Related Emissions and Magnetization Properties of ZnO NanorodsADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Bharati Panigrahy Abstract A clear correlation between defect-related emissions and the magnetization of ZnO nanorods synthesized by a one-step aqueous chemical method is demonstrated. The relative contribution of the emission bands arising from various types of defects is determined and found to be linked with the size of the nanorods and annealing conditions. When the size of the nanorods and the annealing temperature are increased, the magnetization of pure ZnO nanorods decreases with the reduction of a defect-related band originating from singly charged oxygen vacancies (). With a sufficient increase of annealing temperature (at 900,°C), the nanorods show diamagnetic behavior. Combining with the electron paramagnetic resonance results, a direct link between the magnetization and the relative occupancy of the singly charged oxygen vacancies present on the surface of ZnO nanorods is established. [source] Blue Luminescence of ZnO Nanoparticles Based on Non-Equilibrium Processes: Defect Origins and Emission ControlsADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Haibo Zeng Abstract High concentrations of defects are introduced into nanoscale ZnO through non-equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420,nm (2.95,eV,<,Eg,=,3.26,eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488,nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial-zinc-related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as-prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co-emission of blue and green emissions and peak adjustment from blue to yellow. [source] Flame-Synthesized Copper Dimers: Flame-Synthesized Ceria-Supported Copper Dimers for Preferential Oxidation of CO (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Mater. On page 369, R. Kydd et al. describe the creation of highly dispersed copper dimers (violet areas) on Ceria nanoparticles (green areas) via rapid flame-spray pyrolysis. These as-prepared copper dimers, in synergism with the oxygen vacancies in ceria, exhibit favourable electronic and catalytic interactions with incident CO molecules. Consequently, CO can be preferentially oxidised in H2 streams at low temperatures. [source] Nanostructured Titanium Oxynitride Porous Thin Films as Efficient Visible-Active Photocatalysts,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007E. Martínez-Ferrero Abstract Nanocrystalline mesoporous N-doped titania films have been prepared for the first time. The introduction of nitrogen into the anatase structure starts at 500,°C, with N bonding to titanium via oxygen substitution. Increasing the treatment temperature leads to the formation of TiN (TiN1,xOx) and N-doped rutile showing mixed-valence Ti states. Microstructural characterization shows that the ordered mesoporosity is maintained until 700,°C, where TiN (TiN1,xOx) begins to form. Optical characterization shows that the discrete introduction of N is able to shift the titania absorption edge. The photocatalytic tests give the best results under visible light excitation for the film nitrided at 500,°C. At this temperature the concentration of nitrogen in the structure is optimal since oxygen vacancies are still not important enough to promote the recombination of the photogenerated electrons and holes. [source] A Family of Electronically Reconfigurable NanodevicesADVANCED MATERIALS, Issue 37 2009J. Joshua Yang AFM image of 17 nanodevices with a zoom-in cartoon schematically shows an individual crosspoint device consisting of two Pt metal electrodes separated by a TiO2 bi-layer memristive material. By applying an electric field across the memristive material, oxygen vacancies can drift up and down, leading to four current-transport end-states. The switching between these end-states results in a family of nanodevices. [source] A One-Step Method for the Growth of Ga2O3 -Nanorod-Based White-Light-Emitting PhosphorsADVANCED MATERIALS, Issue 35 2009Sampathkumar Chrisolite Vanithakumari A one-step synthesis of Ga2O3 nanorods by heating molten gallium in ambient air at high temperatures is presented. The high-temperature synthesis creates oxygen vacancies and incorporates nitrogen from the environment. The oxygen vacancy in Ga2O3 is responsible for the emission in the blue,green region, while nitrogen in Ga2O3 is responsible for red emission. [source] Structure,Property Relation of SrTiO3/LaAlO3 InterfacesADVANCED MATERIALS, Issue 17 2009Mark Huijben Abstract A large variety of transport properties have been observed at the interface between the insulating oxides SrTiO3 and LaAlO3 such as insulation, 2D interface metallicity, 3D bulk metallicity, magnetic scattering, and superconductivity. The relation between the structure and the properties of the SrTiO3/LaAlO3 interface can be explained in a meaningful way by taking into account the relative contribution of three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. The emerging phase diagram is much richer than for related bulk oxides due to the occurrence of interface electronic reconstruction. The observation of this interface phenomenon is a display of recent advances in thin film deposition and characterization techniques, and provides an extension to the range of exceptional electronic properties of complex oxides. [source] Lanthanum Chromite-Based Interconnects as Key Materials for SOFC Stack DevelopmentINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2004Natsuko Sakai The historical investigations on the physicochemical and transport properties of lanthanum chromite-based perovskite oxides are reviewed to evaluate the compatibility as interconnects in solid oxide fuel cells. These materials improve sinterability in air. This has led to investigations on other physicochemical properties of these materials, such as thermal expansion, mechanical strength, and chemical stability. Lanthanum and chromium ion can be substituted by alkaline earths or transition metals, and this translates into a large flexibility in physicochemical properties. However, the formation of oxygen vacancies in a reducing atmosphere can result in an undesirable isothermal expansion or oxygen permeation. The chemical stability of these materials is governed by the fast cation diffusion at the grain boundary of the polycrystals. [source] Periodic models in quantum chemical simulations of F centers in crystalline metal oxidesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2007Yuri F. Zhukovskii Abstract We present a survey of recent first principles simulations of the neutral oxygen vacancies (F centers) existing as native or radiation-induced point defects in various crystalline metal oxides in different forms (bulk, bare substrate surface, and on the interface with metal adsorbates). We mainly consider periodic models in calculations of point defects using the metal oxide supercell or cyclic clusters. We compare different formalisms of first principles calculations, mostly the Density Functional Theory (DFT) as implemented in the framework of either localized basis set of atomic orbitals or delocalized basis sets of plane waves. We analyze in detail the structural and electronic properties of F centers in binary oxides of light metals (MgO and Al2O3), and ternary metal oxides (SrTiO3, BaTiO3, PbTiO3, KNbO3, and PbZrO3 perovskites). When available, we compare results of ab initio periodic defect calculations with experimental data, results of the first principles cluster calculations (both embedded and molecular) as well as with semi-empirical calculations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] X, -DVM modelling of oxygen transport in YBa2Cu3O7-, and SrFeO3INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2006Elmira I. YuryevaArticle first published online: 4 APR 200 Abstract The reasons for oxygen transport in YBa2Cu3O7-, and SrFeO3 were investigated, using the X, -discrete variation method. Reduced binding energy and other parameters of the electronic energy structure were calculated for a number of crystal fragments within the T and O phases of YBa2Cu3O7-, and the cubic phase of SrFeO3. The following results were obtained: (i) test calculations of reduced binding energy confirmed that high temperature should be a condition of existence of the T phase, as compared with the O phase of YBa2Cu3O7-,; (ii) an increase in temperature up to ,400°C points to the beginning of the Jahn,Teller dynamic effect in SrFeO3; and (iii) transport of neutral and charged oxygen atoms results in distributions of stable and unstable oxygen vacancies, respectively. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Intragranular Voids and dc Degradation in (CaO+MgO) Codoped BaTiO3 Multilayer Ceramic CapacitorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009Hwan-Wen Lee The microstructure of multilayer ceramic capacitors (MLCC) based on BaTiO3 and nickel electrode, have been analyzed using the scanning and the transmission electron microscopy. In order to investigate how MgO improves MLCC against dc degradation, both CaO doped and (CaO+MgO) codoped chips, pristine as well as highly accelerated life-tested, are studied. BaTiO3 grains are characterized by both the types I and II core shell structure, which is typical of MLCC exhibiting the X7R dielectric behavior. Intragranular voids are found in BaTiO3 grains in the vicinity of the electrode,dielectric interface. Void-containing grains are more frequently observed and voids are more abundant in (CaO+MgO) codoped chips than in CaO doped ones. Higher concentration of oxygen vacanciesis induced extrinsically from both MgO codoping and Ni diffusion into BaTiO3 grains along the electrode,dielectric interface during sintering. Such oxygen vacancies have reacted with both cation vacanciesandby an inverse Schottky defect reaction and condensed to form voids. This reaction requiring cation and oxygen vacancies in the stoichiometric BaTiO3 composition of 1:1:3 has significantly decreased the randomly distributed mobile oxygen vacancies, and contributes to improve against dc degradation. [source] Electrode,Ceramic Inter-Diffusion of Ba(Ti,Zr)O3 -Based Y5V MLCCs with Ni ElectrodesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Lei Chen The Ba(Ti,Zr)O3 -based multilayer ceramic capacitors (MLCCs) with Ni electrodes, which meet the Electronic Industry Association Y5V standard (from ,30° to 85°C, at a temperature capacitance coefficient between ,82% and 22%), have been studied in view of the electrode-ceramic inter-diffusion by several microstructual techniques (scanning electron microscopy/transmission electron microscopy/high-resolution transmission electron microscopy (HRTEM)) with an energy-dispersive X-ray spectrometer (EDS). The EDS analysis shows that the elements' inter-diffusion took place along the metal,dielectric interface and the migration of Ni toward the dielectric layers dominated this process. The incorporation of Ni did not transform the crystal structure but introduced lattice distortions, which were characterized by HRTEM, X-ray diffraction, and EDS. The degree of Ni diffusion in the sample with the thinner dielectric layer was more severe. It was concluded from the results that the Ni diffusion is related to the formation of oxygen vacancies after the annealing process, which should be a noticeable factor in the degradation behavior and reliability of base metal electrode MLCCs. The factors influencing the inter-diffusion are also discussed. [source] Dislocation Loops in Pressureless-Sintered Undoped BaTiO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006Yu-Chuan Wu Dislocation loops in pressureless-sintered undoped BaTiO3 ceramics have been analyzed by transmission electron microscopy. The Burgers vector of the loops and its sense b=+1/2[010] were determined using the g·b=0 invisibility criteria, combined with the inside,outside contrast technique using (g·b)sg>0 or<0, keeping the deviation parameter sg>0. The edge-vacancy nature was further ascertained by determining the loop habit plane normal n=[010]. Weak-beam dark-field imaging reveals that loops contained no stacking fault fringes; they are edge-vacancy partial dislocation loops lying in {020} or {010} where parts of the TiO2 or BaO layer are vacant. It is suggested that the extrinsic defects of both cations and oxygen vacancies generated by non-stoichiometry have condensed during sintering in air and are responsible for the formation of such vacancy loops. [source] Phase Transition and Failure at High Temperature of Bismuth-Layered Piezoelectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Liaoying Zheng High-temperature bismuth-layered piezoelectric ceramics (CaxSr1,x)Bi4Ti4O15 have been prepared by the conventional solid reaction method. Our results reveal that there is a "phase transition induced by the composition" taking place in the solid solution at around x=0.4. During transition, the crystal structure changes from orthorhombic to pseudo-tetragonal and then back to orthorhombic. Although all (CaxSr1,x)Bi4Ti4O15 (with any x value) undergo a second-order ferroelectric-to-ferroelectric phase transition at about 200°C below their Curie temperature, only the ceramic with x=0.4 exhibits a failure in piezoelectric properties during the transition. It is suggested that, on the basis of the X-ray photoelectron spectroscopy results, this material failure is induced by the high concentration of oxygen vacancies in the material during the phase transition. [source] Fabrication of Optically Transparent Lead Lanthanum Zirconate Titanate ((Pb,La)(Zr,Ti)O3) Ceramics by a Three-Stage-Atmosphere-Sintering TechniqueJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Yoshiyuki Abe An easy technique has been developed to fabricate optically transparent lanthanum-modified lead zirconate titanate (PLZT) ceramics. This technique consists of three stages: (1) sintering in an oxygen atmosphere, (2) elimination of pores in a carbon dioxide atmosphere, and (3) elimination of oxygen vacancies in an oxygen atmosphere. The carbon dioxide atmosphere enhances the diffusion of oxygen from the pores to outside the sintered body. The experimental results reveal that use of a carbon dioxide atmosphere effectively decreases residual pores and improves optical transmittance. From commercially available raw powders, an optical transmittance of 51% (wavelength of 550 nm) can be achieved for 0.7 mm thick polished PLZT9/65/35 ceramics using a carbon dioxide atmosphere, whereas the value is only 34% without a carbon dioxide atmosphere. The advantage of this technique is that PLZT ceramics having high optical quality can be obtained using conventional sintering tools. [source] Role of Defects on the Aging Behavior of Manganese-Doped Lead Iron Tungstate Relaxor CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Liqin Zhou The effect of oxygen annealing on the dielectric aging of manganese-doped Pb(Fe2/3W1/3)O3 (PFW) ceramics is investigated in an attempt to clarify the role of defects on aging. Evident relaxor-type aging is observed in as-sintered manganese-doped PFW samples. The degree of aging gradually decreases as the annealing time increases, and no aging is observed for 100 h of annealing, which supports the correlation between oxygen vacancies and aging. [source] First-principles study on the concentrations of native point defects in high-dielectric-constant binary oxide materialsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2008J. X. Zheng Abstract The intrinsic concentrations of point defects in high- k binary oxide materials of HfO2, ZrO2, Y2O3 and La2O3 are evaluated on the basis of first-principles calculations. Oxygen defects are found to dominate over a wide range of the oxygen chemical potential. Neutral oxygen vacancies are likely to be responsible for electron trapping in the investigated materials. In HfO2 and ZrO2, oxygen Frenkel pairs are likely to form. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vacancy-mediated room-temperature ferromagnetism in Zn1,xMnxO thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010N. Gopalakrishnan Abstract The effect of oxygen vacancies on ferromagnetism (FM) in Zn1,xMnxO thin films grown by radio frequency (RF) sputtering has been investigated. The grown films at different oxygen pressures have been characterized by X-ray diffraction (XRD), Hall effect, photoluminescence (PL) and vibrating sample magnetometry (VSM). The observed ferromagnetism/diamagnetism by the VSM measurement due to the variation of oxygen vacancies has been confirmed by XRD, PL, and Hall results. The vacancy-mediated FM has been explained by the formation of magnetic polarons. [source] Effects of oxygen ion implantation in spray-pyrolyzed ZnO thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2006K. P. Vijayakumar Abstract ZnO thin films, prepared using the chemical spray pyrolysis technique, were implanted using 100 keV O+ ions. Both pristine and ion-implanted samples were characterized using X-ray diffraction, optical absorption, electrical resistivity measurements, thermally stimulated current measurements and photoluminescence. Samples retained their crystallinity even after irradiation at a fluence of ,1015 ions/cm2. However, at a still higher fluence of 2 × 1016 ions/cm2, the films became totally amorphous. The optical absorption edge remained unaffected by implantation and optical absorption spectra indicated two levels at 460 and 510 nm. These were attributed to defect levels corresponding to zinc vacancies (VZn) and oxygen antisites (OZn), respectively. Pristine samples had a broad photoluminescence emission centred at 517 nm, which was depleted on implantation. In the case of implanted samples, two additional emissions appeared at 425 and 590 nm. These levels were identified as due to zinc vacancies (VZn) and oxygen vacancies (VO), respectively. The electrical resistivity of implanted samples was much higher than that of pristine, while photosensitivity decreased to a very low value on implantation. This can be utilized in semiconductor device technology for interdevice isolation. Hall measurements showed a marked decrease in mobility due to ion implantation, while carrier concentration slightly increased. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dependence of structural and optical properties of Zn1,xCdxO films on the Cd compositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 13 2004D. W. Ma Abstract Zn1,xCdxO alloy semiconductors have great latent applications in short wavelength optoelectronic devices. By the dc reactive magnetron sputtering technique, ternary single-phased Zn1,xCdxO (0 , x , 0.53) alloy crystalline films were prepared on glass and sapphire substrates. For x = 0, 0.20, 0.36, 0.53, the band-gaps of the Zn1,xCdxO alloy films were estimated as 3.28, 3.21, 3.11 and 2.65 eV, respectively. Photoluminescence spectrum shows that the near-band-edge energy of the Zn0.8Cd0.2O film has a red-shift of 0.14 eV from that of pure ZnO reported previously. The green-yellow emission in the photoluminescence spectrum is assumed to mainly related to electron transitions from the single ionized oxygen vacancies (Vo+) to Zn, Cd vacancies (VZn,, VC,d), or oxygen interstice (Oi,). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanical relaxation in tetragonal and orthorhombic phases of (Ba,Sr)TiO3 ceramicsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009H. Y. Wang Abstract Two broad relaxation peaks in the tetragonal and orthorhombic phases, respectively, of BaxSr1,xTiO3 (x,=,0.8 and 1) ceramics were investigated via internal friction and modulus measurements. The activation energy calculated from the Arrhenius relation shows that the relaxation process depends on the thermal history. A possible explanation is proposed that the relaxation during heating is associated with the motion of domain walls, the migration of oxygen vacancies and the interaction between oxygen vacancies and domain walls. In addition, the activation energies of Ba0.8Sr0.2TiO3 are smaller than those of BaTiO3, possibly resulting from the larger interspaces of the two neighbouring Ba2+ and Sr2+ along the c -axis. [source] Ionic and electronic defects in a-BaTiO3 thin films studied by transient and steady state conductivity measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007F. El Kamel Abstract Conduction mechanisms in BaTiO3 films deposited at low temperatures on Cu-electrodes have been investigated in transient and steady regimes as a function of temperatures and electric field. This work aims to identify possible defects which govern the leakage current. Electrical measurements reveal that Space Charge Limited Current (SCLC) constitutes the main leakage mechanism in both the transient and the steady regimes. Based on the theory of SCLC, two types of defects can be detected. At higher temperatures, oxygen vacancies constitute the main defects which migrate across the film to generate an ionic leakage current. Diffusion of these defects is thermally activated with an activation energy around 1 eV. Moreover, at lower temperatures the J - E measurements reveals the presence of a discrete set of shallow traps at 0.45 eV below the conduction band with an effective density of 4 × 1022 m,3. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence of Ho3+:YVO4 crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007S. Polosan Abstract Emission spectra of Ho3+ -doped YVO4 crystals are studied in the visible and infrared spectral regions. Besides the emission bands at 544 nm and at about 1950 and 2017 nm due to Ho3+, we observed a broad emission band at 610 nm at low temperatures like 15 K in the highly doped crystals with the Ho3+ concentrations of more than 0.5 mol%. The excitation band for this broad emission is located at 390 nm which is near the edge of band gap of the crystal. It is suggested that the 610 nm band is attributed to defects related to oxygen vacancies around V4+ ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Laser-induced oxygen vacancy formation and diffusion on TiO2 (110) surfaces probed by photoemission electron microscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006Gang Xiong Abstract Photoemission electron microscopy is used to probe photon-induced oxygen vacancies generated on TiO2 (110)-(1×2) surfaces. An increased oxygen vacancy concentration within the irradiated region leads to an increase of local photoelectron emission. The local oxygen deficient region can be compensated by exposing the surface to molecular oxygen at 1×10,5 Torr, or via surface diffusion at 450 K in vacuum. The surface diffusion coefficient is estimated to be on the order of 10,12 m2/s. Photoemission electron microscopy allows in situ studies of surface electronic defect formation and removal. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation on visible emission control of ZnO thin filmPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004Hong Seong Kang Abstract ZnO thin films were deposited on various substrates and ZnO-Si-ZnO multi-layer thin films were fabricated by pulsed laser deposition (PLD). ZnO thin films showed the three photoluminescence bands centered at around ultraviolet (380 nm), green (490,530 nm) and orange (570,640 nm) region. The region and intensity of visible emission of ZnO thin films were controlled as substrate and annealing treatment. As-grown ZnO thin film showed strong ultraviolet (UV) emission. ZnO thin films on (001) Al2O3 showed the increase of green emission caused by oxygen vacancies in the range of 490 nm to 530 nm, those on (100) InP showed the increase of orange emission caused by oxygen interstitials in the range of 610 nm to 640 nm. The increase of orange emission caused by oxygen interstitials was also observed from ZnO-Si-ZnO multi-layer thin films. The visible emission mechanism of ZnO was investigated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||