The direct determination of the vacancy concentration andP-T phase diagram of Hg0.8Cd0.2Te and Hg0.6Cd0.4Te by dynamic mass-loss measurements

A modified mass-loss measurement technique is employed, for the direct,in- situ determination of the metal vacancy formation in (Hg_1x2212;itxCd _x )_1−y Te _y (s) withx = 0.2 and 0.4. Forx = 0.2, the metal vacancy concentrations are determined between 336 and 660° C for three different compositions(y) within the homogeneity region and range from 2.4 to6.8 x 10¹⁹cm₋₃. The enthalpy of formation of a singly-ionized metal vacancy is derived to be between 0.17 and 0.45 eV depending upon the deviation from stoichiometry (compositiony). Forx= 0.4, three samples of different y-values give the metal vacancy concentrations from 1.9 to 5.5 x 10¹⁹cm⁻³ between 316 and 649° C, and the enthalpy of vacancy formation between 0.25 and 0.40 eV. Compared to the recent data on HgTe(s), these experimental results show a slight but significant decrease in the enthalpy of vacancy formation from HgTe to Hg_0.8Cd_0.2Te, which supports theoretical predictions of the bond weakening effect of Cd for the latter alloy system. Based on the simultaneously determined equilibrium Hg partial pressures within the homogeneity range, the vacancy concentration-partial pressure isotherms are constructed. The Hg partial pressures are also measured along the three-phase boundaries of the solid solutions of bothx = 0.2 and 0.4, and these are in close agreement with published data obtained by optical absorption measurements.     

纳米管钛酸的ESR特性及其可见光照的影响

本报道了纳米管钛酸在真空-0．1MPa、温度100℃的条件下，经过不同时间处理后的ESR特性及其可见光照的影响．发现纳米管钛酸经一定处理后，不经光照即出现g=2．003 ESR信号，该信号是由捕获一个电子的氧空位(Vo)产生的，此信号随着处理时间的延长而增强；在532nm的可见光照射下，随着光照时间的延长信号强度随之增加，达到一定强度值后，不再随光照时间的延长而增加；光源关闭后，信号强度又逐渐减小，但不能恢复到原来信号强度的水平．     

Mechanisms of cavity growth in a fine-grained 7475 Al superplastic alloy

Under creep conditions, cavity growth may be controlled by vacancy diffusion or power-law creep. The two growth mechanisms are examined with reference to a superplastic 7475 Al alloy as a function of test temperature, superimposed strain rate and starting grain size. It is found that power-law cavity growth by plastic deformation of the matrix surrounding the cavities dominates at all test conditions. In addition, growth and interlinkage of cavities is an important parameter in controlling the ease and type of fracture and is enhanced by the ease of superplastic deformation.     

Nitrogen vacancy scattering in GaN grown by metal–organic vapor phase epitaxy

Electron mobility limited by nitrogen vacancy scattering was taken into account to evaluate the quality of n-type GaN grown by metal–organic vapor phase epitaxy. Two assumptions were made for this potential for the nitrogen vacancy (1) it acts in a short range, and (2) does not diverge at the vacancy core. According to the above assumptions, a general expression to describe the scattering potential U(r)=−U₀exp[−(r/β)ⁿ], (n=1,2,…,∞) was constructed, where β is the potential well width. The mobilities for n=1,2, and ∞ were calculated based on this equation, corresponding to the simple exponential, Gaussian and square well scattering potentials, respectively. In the limiting case of kβ1 (where k is the wave vector), all of the mobilities calculated for n=1,2, and ∞ showed a same result but different prefactor. Such difference was discussed in terms of the potential tail and was found that all of the calculated mobilities have T^−1/2 temperature and β⁻⁶ well width dependences. A mobility taking account of a spatially complicate scattering potential was studied and the same temperature dependence was also found. A best fit between the calculated results and experimental data was obtained by taking account of the nitrogen vacancy scattering.     

XPS Studies on Rare Earth Oxide LSCO／YSZ Electrodes

The X-ray diffraction spectra and X-my photoelectron spectroscopy were measured for Sr-doped Lal-xSrx CoO3 materials with perovskite structure prepared by the solid-state reaction method. The influence of heat-treatment tempera-ture on the average crystal size of Lal-xSrx CoO3 was studied. The surface chemical states of Lal-xSrxCoO3 cathodes with different Sr-doped content were discussed. The experimental results show that average crystal size of Lal-xSrxCoO3 under the condition of heat-treatment in the range of 900- 1200℃ is larger than that at other temperatures, which is of benefit to forming porous electrodes. When La is replaced by Sr gradually, the oxygen vacancy concentration increases. It is of benefit to enhancing the transport property of oxygen ion.     

Quenched-in vacancies in B2-structured intermetallic compound FeAl

The concentrations of quenched-in vacancies retained in B2 intermetallic compound Fe_1-cAl_c were obtained as functions of composition (0.39 < c < 0.51) and quenching temperature (773–1273 K) from lattice constant and density measurements. Obtained vacancy concentration indicates rather gradual increase with composition in lower Al content region, while it increased rapidly as the composition approaches to stoichiometric composition. Further, the data for slow-cooled (1 K min⁻¹) samples showed that retained vacancy concentration is higher than that for samples annealed at and quenched from 773 K. Observed lattice constant for each composition decreases linearly with vacancy concentration, which is interpreted in terms of atomic size effect. From changes in vacancy concentration with quenching temperature, apparent vacancy formation energies were estimated. The relation between vacancy concentration and microhardness was also examined. Present results of dependency of lattice constant on heat treatment condition confirm the hardening effect due to retained vacancy. Further, the proposed linear relation of hardness to the square root of vacancy concentration is supported by the present study.     

Bi掺杂BaTiO3陶瓷缺陷性质的第一性原理研究

采用第一性原理计算了Bi掺杂BaTiO3陶瓷3种不同的晶格缺陷结构,分别为单独的BiBa掺杂缺陷模式(BTB模型),1个BiBa掺杂缺陷与1个VBa钡空位同时存在(BTB1模型),符合化学计量比的BiBa掺杂缺陷与VBa钡空位缺陷模式(BTB2模型)。BTB模型显示缺陷结构是由施主掺杂机制控制的,Bi与周围的O原子形成典型的离子键,Ti 4+被还原成Ti 3+。在BTB1模型中钡空位的存在则影响了Bi在晶格中与O的相互作用,Bi偏离初始的中心位置,与邻近的3个氧原子形成了弱的共价键,而正是由于这些弱的共价键导致缺陷附近的[TiO6]八面体产生较大畸变,削弱了Ti 4+的极化能力,使缺陷附近的[TiO6]八面体极化能力减弱,此时缺陷结构是由Ba2+离子空位补偿机制控制的。而BTB2模型可以看成是BTB模型与BTB1模型的叠加,因此缺陷结构是由施主掺杂机制与Ba2+离子空位补偿机制共同控制的。     

Electrical conductivity of cobalt doped La0.8Sr0.2Ga0.8Mg0.2O3−δ

La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM8282), La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O_3−δ (LSGMC5) and La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O_3−δ (LSGMC8.5) were prepared using a conventional solid-state reaction. Electrical conductivities and electronic conductivities of the samples were measured using four-probe impedance spectrometry, four-probe dc polarization and Hebb–Wagner polarization within the temperature range of 973–1173 K. The electrical conductivities in LSGMC5 and LSGMC8.5 increased with decreasing oxygen partial pressures especially in the high (>10⁻⁵ atm) and low oxygen partial pressure regions (<10⁻¹⁵ atm). However, the electrical conductivity in LSGM8282 had no dependency on the oxygen partial pressure. At temperatures higher than 1073 K, PO₂$P_{{\text{O}}_2}$ dependencies of the free electron conductivities in LSGM8282, LSGMC5 and LSGMC8.5 were about −1/4, and PO₂$P_{{\text{O}}_2}$ dependencies of the electron hole conductivities were about 0.25, 0.12 and 0.07, respectively. Oxygen ion conductivities in LSGMC5 and LSGMC8.5 increased with decreasing oxygen partial pressures especially in the high and low oxygen partial pressure regions, which was due to the increase in the concentration of oxygen vacancies. The change in the concentration of oxygen vacancies and the valence of cobalt with oxygen partial pressure were determined using a thermo-gravimetric technique. Both the electronic conductivity and oxygen ion conductivity in cobalt doped lanthanum gallate samples increased with increasing concentration of cobalt, suggesting that the concentration of cobalt should be optimized carefully to maintain a high electrical conductivity and close to 1 oxygen ion transference number.