Littérature scientifique sur le sujet « Defects - Polycrystalline Oxides »

Abstract This review encompasses properties and applications of polycrystalline or amorphous, Transparent Conducting Oxides (TCO) semiconductors. Coexistence of electrical conductivity and optical transparency in TCO depends on the nature, number and atomic arrangements of metal cations in oxides, on the resident morphology and presence of intrinsic or introduced defects. Therefore, TCO semiconductors that are impurity-doped as well as the ternary compounds and multi-component oxides consisting of combinations are discussed. Expanding use of TCO is endangered by scarcity, cost of In, fragility of glass, limited transparency to visible light, instability above >200 °C, non-flexible for application of flexible solar cell; thus driving search for alternatives such as graphene or CNT, that are more stable under acidic, alkaline, oxidizing, reducing and elevated temperature. There are reasons to conclude that there is need to develop large area deposition techniques to produce TCO films with high deposition rate. TCOs are mostly n-type semiconductors, but p-type are also being researched

ZnO varistors are multicomponent polycrystalline ceramics with highly nonlinear current-voltage characteristics and surge energy absorption capabilities. The voltage gradient of the ZnO varistor is inversely proportional to its average grain size. Recently, the rare-earth oxides have been reported as growth inhibitor of ZnO grains to obtain high voltage gradient. Although the dopant of rare-earth oxides can remarkably enhance the voltage gradients of varistor samples, their leakage currents and nonlinear coefficients deteriorate at the same time. In this paper, the sintering effects on electrical characteristics and admittance spectroscopies of ZnO varistor samples doped with yttrium oxides were investigated. Samples were fabricated under different sintering temperatures, including 1000 °C, 1100 °C, 1200 °C and 1300 °C. Then, the electrical characteristics and admittance spectroscopies of these varistor samples were measured. The measured current-voltage results behave special U-type curves related to sintering temperature. Furthermore, the admittance spectroscopy of these samples revealed the sintering effects on the intrinsic defects of ZnO varistors.

The thermal expansion coefficient (TEC) of binary glasses SiO2-TiO2 decreases as the TiO2 concentration grows. At concentration of TiO2 in the range of 4-6 mol% (in dependence of the applied synthesis method) TEC becomes negative; at concentration of 8-11 mol% devitrification occurs. A combination of photoluminescence (PL) and IR reflection techniques were applied for studying the evolution of point and structural defects in the range of TiO2 concentration from zero to phase separation. The precision measurements of density showed its drop at TiO2 content of 7.9 mol% thus evidencing the conversion of glass into a polycrystalline substance consisting of SiO2 and TiO2 crystallites. In the TiO2 concentration range of compatibility of oxides, an ensemble of point defects comprises =SiO-Si= and =Ti-O- centers as well as =Si-Si= and =Si-Ti= neutral oxygen-vacancies. At the dopant concentration specific for phase separation (TiO2 7.9 mol%), the PL-active groups of =Si-Ti= go away, while the IR-detectable Si-O-Ti bridges remain stable. Keywords: SiO2-TiO2 glass, point defects, structural defects, photoluminescence, IR spectroscopy.

It is known from many published data on amorphous or polycrystalline silicon and on metal oxides based Thin Film Transistors (TFTs) that their electrical parameters improve when decreasing the thickness of the channel layer. The origin of this improvement is discussed here through electrostatic arguments only. In particular, it is shown that the behavior of the subthreshold swing with the thickness does not depend on the type of materials. The material and its electrical defects determine only the importance of the improvement but not the trend towards better electrical parameters. Meanwhile, in general, the electrical stability under gate stress enhances too. The improved stability is explained by the reduced electronic charge inside the channel layer, leading to a lower injection of electrons in the gate insulator.

The electrical characteristics of TiO2films grown on III-V semiconductors (e.g., p-type InP and GaAs) by metal-organic chemical vapor deposition were studied. With (NH4)2S treatment, the electrical characteristics of MOS capacitors are improved due to the reduction of native oxides. The electrical characteristics can be further improved by the postmetallization annealing, which causes hydrogen atomic ion to passivate defects and the grain boundary of polycrystalline TiO2films. For postmetallization annealed TiO2on (NH4)2S treated InP MOS, the leakage current densities can reach2.7×10−7and2.3×10−7 A/cm2at±1 MV/cm, respectively. The dielectric constant and effective oxide charges are 46 and1.96×1012 C/cm2, respectively. The interface state density is7.13×1011 cm−2eV−1at the energy of 0.67 eV from the edge of valence band. For postmetallization annealed TiO2on (NH4)2S treated GaAs MOS, The leakage current densities can reach9.7×10−8and1.4×10−7at±1 MV/cm, respectively. The dielectric constant and effective oxide charges are 66 and1.86×1012 C/cm2, respectively. The interface state density is5.96×1011 cm−2eV−1at the energy of 0.7 eV from the edge of valence band.

We demonstrated the possibility of using the mathematical form of Darken's theory, applied to the description of the Kirkendall effect in binary systems, to the description of reactive interdiffusion in non-stoichiometric polycrystalline film oxide systems with limited solubility. The aim of the study was the simulation of reactive interdiffusion under vacuum annealing of a thin film system consisting of two non-stoichiometric polycrystalline titanium and cobalt oxides. The nonstoichiometric nature of the system assumes the presence of mobile components, free interstitial cobalt and titanium cations in it. Phase formation occurs as a result of reactive interdiffusion and trapping of mobile components of the systemon inter-grain traps. The proposed mechanism describes the formation of complex oxide phases distributed over the depth of the system.A complex empirical research technique was used, involving Rutherford backscattering spectrometry, X-ray phase analysis and modelling methods. The values of the characteristic parameters of the process were determined by numerical analysis of the experimentally obtained distributions of the concentrations of the components within the developed model. During vacuum annealing of a thin film two-layer system of non-stoichiometric TiO2–x–Co1–уO oxides in temperature range T = 773 – 1073 К, the values of the individual diffusion coefficients of cobalt DCo = 5.1·10–8·exp(–1.0 eV/(kT) cm2/s and titaniumDTi = 1.38·10–13·exp(–0.31 eV/(kT) cm2/s were determined.It was shown that for T = 1073 K, the phase formation of CoTiO3 with a rhombohedral structure occurs. The extension of the phase formation region of complex cobalt and titanium oxides increases with an increase in the vacuum annealing temperature and at 1073 K it is comparable with the total thickness of the film system.The model allows predicting the distribution of the concentrations of the components over the depth of multilayer nonstoichiometric systems in which reactive interdiffusion is possible. References1. Chebotin V. N. Fizicheskaya khimiya tverdogo tela[Physical chemistry of a solid state]. Moscow: KhimiyaPubl.; 1982. 320 p. (in Russ.)2. Tretyakov Yu. D. Tverdofaznye reaktsii [Solidphase reactions]. Moscow: Khimiya Publ.; 1978. 360 p.(in Russ.)3. Afonin N. N., Logacheva V. A. Interdiffusion andphase formation in the Fe–TiO2 thin-film system.Semiconductors. 2017;51(10): 1300–1305. DOI: https://doi.org/10.1134/S10637826171000254. Afonin N. N., Logacheva V. A. Cobalt modificationof thin rutile films magnetron-sputtered in vacuumtechnical. 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The thermal expansion coefficient (TEC) of binary glasses SiO 2 -TiO 2 decreases as the TiO 2 concentration grows. At concentration of TiO 2 in the range of 4–6 mol% (in dependence of the applied synthesis method) TEC becomes negative; at concentration of 8–11 mol% devitrification occurs. A combination of photoluminescence (PL) and IR reflection techniques were applied for studying the evolution of point and structural defects in the range of TiO 2 concentration from zero to phase separation. The precision measurements of density showed its drop at TiO 2 content of 7.9 mol% thus evidencing the conversion of glass into a polycrystalline substance consisting of SiO 2 and TiO 2 crystallites. In the TiO 2 concentration range of compatibility of oxides, an ensemble of point defects comprises ≡Si–O – and ≡Ti–O – centers as well as ≡Si–Si≡ and ≡Ti–Ti≡ neutral oxygen-vacancies. At the dopant concentration specific for phase separation (7.9 mol%), the PL-active groups of Si–Ti go away, while the IR-detectable Si–O–Ti bridges remain stable.

Polycrystalline stoichiometric Co-substituted ZnO oxides have been synthesized by solid state reaction via sintering ZnO and Co powders in air. The precise nature of magnetic coupling is determined by studying carefully structural and magnetic properties. The magnetization as a function of temperature for Zn1-xCoxO (x = 0.02, 0.05, 0.0625 and 0.10) can be fitted well to a model with a paramagnetic Curie term, an antiferromagnetic Curie-Weiss term and a diamagnetic constant, which could arise from spins of isolated Co ions, grouped Co ions that are in nearest neighbor positions and a diamagnetic background, respectively. The substitution of Co at the Zn sites does not occur in a completely random manner but the Co ions appear to have a tendency for grouping. It is interesting to note in Raman measurements that host lattice defects with 2 distinct impurity modes may be induced by isolated and grouped Co spins.

Accurate characterization of chemical strain is required to study a broad range of chemical-mechanical coupling phenomena. By combining density functional theory (DFT) calculations and elastic dipole tensor theory, it is readily to predict the long-range chemical strain tensor and the chemical expansion coefficient tensor induced by dilute point defects in a crystal structure. First, we demonstrate that, even in cubic CeO2-δ, both the short-range deformation surrounding an oxygen vacancy and the long-range chemical strain (or the expansion coefficient) are anisotropic. The origin of this anisotropy is the charge disproportionation between the four cerium atoms surrounding each oxygen vacancy (two become Ce3+ and two become Ce4+) when a neutral oxygen vacancy is formed. While the short-range deformation agrees with experimentally determined Ce-O bond lengths, the predicted maximum and average chemical strains successfully bound the variety of CeO2-δ chemical strain behavior previously reported in the literature. Normally, since there are six possible disproportionation configurations, the average chemical strain is isotropic. Only under an external bias, such as an applied electric field, the chemical strain can be oriented to show the anisotropic effect. This successfully explained the giant electrostriction effect reported in doped and un-doped CeO2-δ. Next, we show strains induced by coupled vacancies in layered Li-intercalation compounds for battery applications. Li2MnO3 was investigated as Li-excess intercalation compounds containing Li2MnO3 need to be “activated” to deliver the high capacity. This activation process during the first delithiation cycle at a high voltage is believed to introduce oxygen vacancies into the system. Due to the large amount Li vacancy generated, a large number of defect configurations were sampled and the average chemical strain induced by Li vacancy concentration is obtained by Boltzmann average. Previously, we have demonstrated that it is energetically favorable to create a Li-O-Li vacancy dumbbell structure (VLi - VO - VLi) in Li2MnO3. The chemical strain of the vacancy dumbbell structure is smaller than the sum of the chemical strain of one Vo and two VLis. The chemical expansion coefficient averaged for the polycrystalline samples and the experimentally measured stress change provided a novel method to in situ track the irreversible chemical changes in Li-excess cathode materials.

Tracer self-diffusion of Ba and Y and the diffusion of Dy, Ho, and Gd, which substitute for Y, have been measured in polycrystalline YBa2Cu3Ox over temperature and oxygen partial pressure ranges of 850 to 980 °C and 103 to 105 Pa, respectively. The diffusion of Ba is slower than that of oxygen or copper, with a high activation energy of about 890 ± 80 kJ/mole. Large anisotropy has also been observed, with diffusion along the c-axis being more than three orders of magnitude slower than diffusion in randomly oriented polycrystals. Diffusion coefficients of Ba were, within experimental uncertainty, independent of oxygen partial pressure over the range measured. The diffusion coefficients of the Y-site species were nearly identical and an activation energy of about 1.0 MJ/mole was estimated, in agreement with that for high-temperature deformation. Attempts to speed up the kinetics through creation of point defects on the Y site by doping proved to be unsuccessful. These results are compared to cation diffusion in cubic perovskites and simple oxides.

The structural changes in polycrystalline indium oxide were studied before and after irradiation of samples, Xe+ ions with energy 140 and 300 keV, X-ray methods. Discovery, that irradiation leads to a change in the chemical composition of the oxide, accompanied by phase transformations. The main structure of the cubic oxide after irradiation contain macro and micro stresses, which depend on the energy irradiation. The increase in the relative integral intensity of radiation reflected from the planes of the cell on depth was observed. The maximum value observed at a depth of 1.5 m from the plane (510). The analyses of reflected the radiation found that the flux of photons remains constant - the atomic nuclei of oxide not change, increases the frequency, decreases the wavelength depend from the energy irradiation. In some directions in reflecting from the planes, the atoms are formed with different electron density, that connect whit presence of defects, which leads to appear of the forced oscillation, which increases the relative integral intensity of the reflected radiation. These processes are damped with increasing depth of the sample. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35411

In the process of studying the mechanisms of influence of structural defects on properties in scandium oxide, the thermal and electrical effects in the temperature range 25 – 1800 C in a vacuum, in the struc-ture was of detected a gradual phase transition of the ordered cubic type C in a disordered type C1 in the temperature range of 400 – 1000 C. Phase transformation is accompanied by the difference of the conduc-tivity type of the charge carriers. Anion conductivity of charges in the structure of scandium oxide exist there is to 400 С, with the energy of conductivity charges 2.46 eV. In scandium oxide in the interval tem-peratures 400 – 1000 C in case there is a mixture of two types of conductivity anion and electronic. In the interval of temperatures 1600 – 1800 C in case there is a change of the chemical composition of the oxide on the content of oxygen. With the help of the mathematical model of calculation of the elements of the structure of the change in the size of the radii of oxygen and anionic vacancies, which coincides with the change of parameters of elementary cells in the transition of the structure of C in C1. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35390