Journal of Physics and Chemistry of Solids
The tetragonal distortion for the tetragonal V2+-V-M center in KBr:V2+ crystal is estimated by analyzing its EPR data from two theoretical models, one is the two spin-orbit (S.O.) parameter model where the contributions to EPR parameters from both the S.O. coupling of the central metal ion and that of the ligands are considered and another is the conventional one-S.O.-parameter model where only the contribution from the S.O. coupling of the central metal ion is included. The result from the two-S.O.-parameter model is more than ten times that of the one-S.O.-parameter model. The reasonableness of the former is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.
关键词:
inorganic compounds;crystal fields;defects;electron paramagnetic;resonance (EPR);epr parameters;transition;ions
Journal of Physics-Condensed Matter
We investigated the stable (0001) surfaces of M(2)AlC (M = Ti, V and Cr) using the first-principles plane-wave pseudopotential total energy method. Four possible (0001) terminations were considered by breaking the M-Al and M-C bonds. The corresponding surface energies were calculated and compared. The Al-and M(C)-terminated (0001) surfaces demonstrated better stability than the C- and M(Al)-terminated surfaces by their much lower surface energies. In addition, the stability of surfaces was predicted under various chemical environments as a function of chemical potentials. We further investigated the character of surface relaxations. The electronic structures of the stable Al- and M(C)-terminated surfaces were analyzed.
关键词:
ab-initio calculations;ti3sic2 thin-films;electronic-structure;elastic stiffness;al;deposition;cr2alc;simulation;adhesion;solids
Journal of Physics and Chemistry of Solids
In this paper, the high-order perturbation formulae of zero-field splitting D, E and g factors g(x), g(y), and g(z) for d(3) ions in rhombic symmetry are established by using a two spin-orbit (S.O.) parameter model in which the contributions due to both the S.O. coupling of the central d(3) ions and that of the ligands are considered. Based on these formulae, the local structural parameters of the rhombic defect centers V2+-V-M (i.e, the V2+ ion and a host metal ion vacancy V-M) in MCl:V2+ (M = Li, Na) crystals are estimated by calculating their EPR parameters. The results are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.
关键词:
inorganic compounds;crystal fields;defects;electron paramagnetic;resonance (EPR);ions
Physica Status Solidi B-Basic Research
The high-order perturbation formulas of zero-field splitting D and gyromagnetic factors g(parallel to) and g(perpendicular to) for 3d(3) ions in tetragonal symmetry are established by using a two-spin-orbit(SO)-parameter model where the contributions to these EPR parameters from both the SO coupling of the central 3d(3) ions and that of the ligands are considered. From these formulas, the local structural parameters for the tetragonal V2+-V-M centers in MCl:V2+ (M = Na, K, Rb) crystals are estimated from the EPR data. The results are compared with those obtained from the conventional one-SO-parameter model where only the contribution of the SO coupling of central 3d(3) ions is included. The reasonableness of the results based on the two-SO-parameter model is discussed.
关键词:
ions
葛红卫
,
王新华
,
张琰
,
李慧
,
陈立新
,
李寿权
,
严密
,
陈长聘
功能材料
为改善Ti(Cr-Mn)2 AB2型合金的储氢性能,采用A侧过化学计量和过渡金属部分替代Mn进行多元合金化,系统研究了Tix(Cr-Mn-M)2(x=1.0,1.1;M=V、Fe、Ni、Cu)合金的储氢性能.研究结果表明,V、Fe、Ni、Cu部分替代Mn进行多元合金化后,合金主相仍保持C14(MgZn2)型Laves相,合金晶胞体积增大.合金化元素部分替代Mn后合金的活化性能得到明显改善,合金吸放氢量增大,吸放氢压力滞后减小.除Fe使合金放氢平台压力有所升高外,其余合金化元素均使合金的吸放氢平衡压力有不同程度的降低,这是由于合金的晶胞体积增大所致.在所形成的合金中,以Ti1.1Cr1.2Mn0.5CuO0.3的综合性能最好,其室温下吸放氢量分别达到1.95%和1.72 9,6(质量分数).采用该合金与自制的轻质高压储氢容器(工作压力为40MPa)复合组成金属氢化物复合式高压储氢器,对其储氢密度的计算结果表明,当储氢合金的填充量(体积分数)达到0.20时,该复合式储氢器总的体积储氢密度将提高57%.
关键词:
储氢合金
,
金属氢化物
,
储氢容器
,
高压氢
胡标
,
尹明
,
王庆平
,
闵凡飞
,
杜勇
兵器材料科学与工程
基于文献报道的实验数据,采用相图计算(CALPHAD:CALculation of PHAse Diagrams)方法对V-M(M=Li,Na,K,Sc,Ag)5个二元系进行相图热力学研究.通过热力学优化计算获得了一套描述液相、(V)、(Li)、(Na)、(K)、(αSc)、(βSc)和(Ag)相的热力学参数.V-Li、V-Na和V-K体系中的气相视为由组元V、Li、Li2、Na、Na2、K和K2混合的理想气体.与实验相图数据对比表明,获得的热力学参数能够准确地描述实验相平衡数据.
关键词:
V-M(M=Li,Na,K,Sc,Ag)
,
CALPHAD方法
,
相图
,
热力学模型
Spectrochimica Acta Part a-Molecular and Biomolecular Spectroscopy
The spin Hamiltonian parameters (zero-field splitting D, g factors g(parallel to), g(perpendicular to) and hyperfine structure constants A(parallel to), A(perpendicular to)) for M2+ (M = Co, Mn, V and Ni) ions in CsMgCl3 are studied by using the perturbation formulas of the spin Hamiltonian parameters for 3d(n) (n = 7, 5, 3, 8) ions in trigonal symmetry based on the cluster approach. In these formulas, the contributions to the spin Hamiltonian parameters from the admixture of d orbitals of the central ions with the p orbitals of the ligands and from the trigonal distortion are included and the parameters related to these effects can be obtained from the optical spectra and the local structures of the studied systems. Based on the studies, it is found that the local trigonal distortion angle beta in the M2+ impurity center is unlike that beta(H) (approximate to51.71degrees) in the host CsMgCl3. The spin Hamiltonian parameters for these divalent ions in CsMgCl3 are also satisfactorily explained by using the local angle beta. The validity of the results is discussed. (C) 2003 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance;crystal-field theory and spin;Hamiltonians;local structure;m2+(M = Co, Mn, V and Ni);CSMgCl3;acoustic paramagnetic resonance;atomic screening constants;superposition model;tetragonal symmetry;crystal-structure;epr;parameters;scf functions;sites;absorption;fluoride
Physical Review B
We investigate the elastic stiffness and electronic band structure of nanolaminate M2AlC (M=Ti,V,Nb, and Cr) ceramics by using the ab initio pseudopotential total energy method. The relationship between elastic stiffness and valence electron concentration (VEC) is discussed. The results show that the bulk and shear moduli enhance monotonously as VEC increases in M2AlC. The shear modulus c(44), which by itself represents a pure shear shape change and is directly related to hardness, reaches its maximum when the VEC is in the range of 8.4-8.6. This implies that the bulk modulus, shear modulus, and hardness vary in different trends when the VEC changes in M2AlC. Furthermore, trends in the elastic stiffness are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level of M2AlC. We show that increments of bulk and shear moduli originate from additional valence electrons filling states involving Md-Alp covalent bonding and metal-to-metal t(2g) and e(g) orbitals. For the case of c(44), strengthening the M-Al pd covalent bonds effectively enhances the shear resistance and excessive occupation of dd orbitals gives rise to a negative contribution. The maximum of c(44) is attributed to the complete filling of the Md-Alp bonding states.
关键词:
mechanical-properties;ti;behavior;ti3sic2;phases;solids
