W Liang~1
,
2)
,
Q. Li~2) and D.ZYang~2)(Centre of Measuring and Testing Taiyuan University of Technology
,
Taiyuan 030024
,
China Institute of Materials Science and Engineering
,
Harbin Institute of Technology
,
Harbin 150001 China Manuscript received 13 November 1995)
金属学报(英文版)
An in situ study of twinning at crack tip in a TiAl-base alloy has been performed.The result shows that twinning with long shear vector(2/6) [112] can generate on(111) plane, even though usually it is very difficult to occur because of the high energy barrier. It was further shown that (1/6) [112](111) twinning is considerably easier to generate. Furthermore,(1/2)<110) ordinary dislocations were very active and dominated nearly the whole plastic zone, in spite of low Schmid factors. On the other hand, however <101) and (1/2) <112] superdislocations with higher Schmid factors can hardly be observed.
关键词:
:TiAl-base alloy
,
null
,
null
Pramana-Journal of Physics
By calculating the optical spectrum band positions and EPR parameters (g factors, g(parallel to), g(perpendicular to) and zero-field splitting D) by diagonalizing the complete energy matrix of 3d(8) ions in trigonal symmetry, the defect structure of Ni2+ centre in alpha-LiIO3 crystal is studied. It is found that to reach the good fits of optical and EPR data between calculation and experiment, the Ni2+ ion should shift by Delta z approximate to 0.298 angstrom along C-3-axis and the O-2-ions between the Ni2+ ion and Li+ vacancy (V-Li) should be displaced away from the V-Li by Delta x approximate to 0.097 angstrom because of the electrostatic interaction. The results are discussed.
关键词:
Optical spectra;electron paramagnetic resonance;defect structure;Ni2+;alpha-LiIO3.;field;ions;cr3+;temperature;parameters;epr;pressure;model;liio3
Physica Status Solidi B-Basic Research
The perturbation formulae of EPR g-factors g(i) (i = x, y, z) and hyperfine constants Ai for a 3d(7) (Co2+) ion at a rhombic octahedral site in a crystal are established from a cluster approach. In these formulae, the contributions from the covalency effect, the configuration interaction and the rhombic crystal field are considered and the parameters used in the calculation of EPR parameters. except the core polarization constant x in the calculation of Al, can be estimated from the optical spectra and the structure data of the studied system. From these formulae, the EPR parameters g(i) and A(i) for the rhombic Co2+-V-Ag centre in AgCl are reasonably explained by considering suitable rhombic distortion and so the microstructure of this rhombic centre is obtained.
关键词:
superposition model;crystals
Physica Status Solidi B-Basic Research
The EPR g-factors g(\\), g(perpendicular to) and hyperfine structure constants A(\\), A(perpendicular to) for a tetragonal Co2+ centre, i.e.. Co(H2O)(2)Cl-4 centre, in NH4Cl crystal are calculated from the perturbation formulas based on a cluster approach. In these formulas, the parameters related to the contributions from the configuration interaction. the covalency effect and the low-symmetry crystal field can be obtained from the optical spectra and the structural model and data of the studied system. The core polarization constant it in the calculation formulas of hyperfine constants is used as an adjustable parameter. The calculated results are in good agreement with the observed values.
关键词:
superposition model;centers;resonance;ions;cr3+
Xiujian Chou
材料科学技术（英文）
Ba1-xSrxTiO3 ceramics, doped with B2O3-Li2O glasses have been fabricated via a traditional ceramic process at a low sintering temperature of 900 °C using liquid-phase sintering aids. The microstructures and dielectric properties of B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have been investigated systematically. The temperature dependence dielectric constant and loss reveals that B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have diffusion phase transformation characteristics. For 5 wt% B2O3-Li2O glasses doped Ba0:55Sr0:45TiO3 composites, the tunability is 15.4% under a dcpplied electric field of 30 kV/cm at 10 kHz; the dielectric loss can be controlled about 0.0025; and the Q value is 286. These composite ceramics sintered at low temperature with suitable dielectric constant, low dielectric loss, relatively high tunability and high Q value are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential microwave tunable devices applications.
关键词:
Sintering
雷强华
,
陈长安
,
黄理
,
张永彬
稀有金属材料与工程
基于量子力学第一性原理,采用赝势平面波函数与密度泛函结合的方法,计算并研究V、VH_2、VD_2、VT_2体系的晶格动力学特征及热力学函数,采用热力学方法分析钒吸氢生成VQ_2(Q=H,D,T)的热力学同位素效应.晶格动力学性质研究表明,VQ_2的热力学同位素效应主要是氢同位素在钒晶格中的振动频率不同导致的.VQ_2生成反应在10~1000 K的温度范围内标准吉布斯自由能变由-50 kJ·mol~(-1)近似线性上升至140 kJ·mol~(-1).平衡压力与温度关系表明,在高于常温的条件下,平衡压力随温度急剧升高;钒吸附氢同位素生成二氢化钒在整个温度范围内均表现为负同位素效应.
关键词:
钒
,
氢
,
同位素效应
,
热力学
Physica Scripta
The g factors g (parallel to) and g (vertical bar) of the isolated tetragonal Cu(II)O-5 cluster in YBa2Cu3O7-delta superconductors induced and suppressed by mechanical processing are calculated from the complete diagonalization (of the energy matrix) method (CDM) and the perturbation theory method (PTM). Both methods are based on the cluster approach where in addition to the contribution of the spin-orbit parameter of the central metal ion, the contribution of ligand ion via the covalence effect is taken into account. In the calculations, the structural data of the Cu(II)O-5 cluster gained from x-ray diffraction are applied. The results from both the CDM and the PTM are similar and show reasonable agreement with the experimental values. It appears that both methods can be used to explain the EPR g factors for d(9) ions in crystals.
关键词:
electron-paramagnetic-resonance;spin-hamiltonian parameters;atomic;screening constants;temperature-dependence;crystal-field;single-crystals;gyromagnetic factor;scf functions;ions;yba2cu3o6+x
XU Ji-fang
,
ZHANG Jie-yu
,
JIE Chang
,
TANG Lei
,
CHOU Kuo-chih
钢铁研究学报(英文版)
The densities of the selected quaternary CaO-MgO-Al2O3-SiO2 slag with low silica were measured by the Archimedean method in a wide temperature range from 1773 to 1873 K. Nine different slag compositions were chosen based on three different levels of CaO content and three different levels of SiO2 content. wMgO was equal to 7.0%. wCaO were varied from 40.04% to 50.64%, for wSiO2=10.25%-20.70%. The effects of temperature, SiO2 content and optical basicity were studied. It is shown that density decreases approximately linearly with an increase in temperature. Under the same CaO content, the density decreases with increasing of SiO2 content, and increases with optical basicity increasing. Based on the experimental data as the boundary of the homogenous phase region predicated by FACTSAGE software, the mass triangle model is used to calculate the density of selected limited homogenous phase region. The results showed that the mass triangle model works well.
关键词:
density
,
slag
,
low silica
,
optical basicity
,
model
Solid State Ionics
A method for oxygen leak rate testing was presented based on oxygen pump technique. In this method, using the theory of oxygen pump and oxygen sensor, a formula for the calculation of leak rate was derived from Nernst equation, Faraday law and ideal gas law. In the gas leakage testing, a glass sealant based on SiO2-B2O3-Al2O3-BaO-PbO2-ZnO (named AF8) was used to seal two yttria stabilized zirconia (YSZ) plates together to form a small gas chamber, one plate worked as oxygen pump and the other worked as oxygen sensor. Constant current was applied on the oxygen pump to take out/into oxygen from the gas chamber resulting in its oxygen partial pressure change, the corresponding concentration voltage data were collected continuously for the calculation of the oxygen leak rate. With this method, the calculated leak rate of AF8 was 8.2 x 10(-8) mbar 1 s(-1) cm(-1) at 800 degrees C which was smaller than the required value of 10(-7) mbar 1 s(-1) cm(-1). (C) 2008 Elsevier B.V All rights reserved.
关键词:
oxygen pump;oxygen sensor;glass sealant;leak rate;compressive mica seals;oxide fuel-cells;chemical diffusion;surface;exchange;zirconia
