M. P. Tosi(International Centre for Theoretical Physics
,
Strada Costiera 11
,
I-34014 Trieste
,
Italy)
材料科学技术（英文）
Solutions of metals in molten salts present a rich phenomenology: localisatlon of electrons in disordered ionic media, activated electron transport increasing with metal concentration towards a nonmetal-metal (NM-M) transition, and liquid-liquid phase separation. A brief review of progress in the study of these systems is given in this article, with main focus on the NM-M transition. After recalling the known NM-M behaviour of the component elements in the case of expanded fluid alkali metals and mercury and of solid halogens under pressure, the article focuses on liquid metal-molten salt solutions and traces the different NM-M behaviours of the alkalis in their halides and of metals added to polyvalent metal halides.
关键词:
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+
Physica Status Solidi B-Basic Research
The spin Hamiltonian parameters, g factors and the hyperfine structure constants for Co4+ (3d(5)) and Ir4+ (5d(5)) in SrTiO3 are theoretically studied from the formulas of these parameters for an nd(5) (n = 3 and 5) ion in a tetragonally distorted octahedron with low spin S = 1/2. According to the theoretical analyses, the impurity-ligand bond lengths R-parallel to' parallel to the C-4 axis are found to be larger than the host values R-parallel to based on the phase transition rotation angles phi of the [TiO6](8-) octahedron by the C-4 axis at 4.2 and 77 K, respectively. The elongation of the ligand octahedra in the host may be enhanced in the impurity centers by the Jahn-Teller effect of the nd(5) ions. The theoretical results based on the above local structures show good agreement with the experimental data.
关键词:
electron-paramagnetic-resonance;atomic screening constants;phase-transition;optical-absorption;scf functions;doped srtio3;degrees k;crystals;ions;spectra
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
Journal of Physics and Chemistry of Solids
A theoretical method for investigating the inter-relation between the molecular structure and electronic structure has been established on the basis of the 252 x 252 complete energy matrices for a 3d(5) configuration ion in a tetragonal ligand field. By means of this method, which is independent of the X-ray diffraction, the local structure of the paramagnetic Mn2+ ion in perovskite fluorides A(2)MF(4) (A = K, Rb; M = Zn, Me. Cd) are determined directly by analyzing the EPR spectrum of octahedral Mn2+ center in A(2)MF(4) crystals and the optical absorption spectrum of the (MnF6)(4-) cluster. It is shown that, comparing with the octahedral cubic structure, the local microstructure in the vicinity of Mn2+ displays an elongated distortion when b(2)(0) > 0 and a compressed distortion when b(2)(0) < 0, and Delta R vs. 10(4)b(2)(0) as well as Delta R vs. 10(4)b(4)(0) in the distortion region is, respectively, approximately linear. Simultaneously, the theoretical zero-field-splitting parameters b(2)(0), b(4)(0) and b(4)(4) are in good agreement with the experimental values. (c) 2006 Elsevier Ltd. All rights reserved.
关键词:
crystal fields;crystal structure;electronic structure;zero-field splittings;crystals;ions;spectroscopy;luminescence;resonance;epr
Chemical Physics Letters
A theoretical method for investigating the inter-relation between the electronic and the molecular structures of a d(5) ion in a tetragonal ligand-field has been established on the basis of a 252 x 252 complete energy matrix. Using this method, the local structure parameters of the Fe3+-V-M system in AMF(3):Fe3+ crystals are determined by the experimental EPR spectra at T = 300 K. It is shown that, the local lattice structure around an octahedral Fe3+ center has a compression distortion along the crystalline axis in AMF(3):Fe3+ crystal. From our analysis, we also conclude that Delta R vs. 10(4)b(2)(0) is approximately linear for the Fe3+-V-M system in AMF(3):Fe3+ crystals. (c) 2006 Elsevier B.V. All rights reserved.
关键词:
electron-paramagnetic-resonance;spin-hamiltonian parameters;epr-spectra;ions;kznf3;phase;exafs;laser;field;site
齐召庆
,
汪宏涛
,
薛明
功能材料
doi:10.3969/j.issn.1001-9731.2016.02.010
采用改进的非接触式混凝土收缩测定仪及标靶,研究了m(M)/m(P)比值(MgO与KH2PO4的质量比)对磷酸镁水泥石自收缩行为的影响,运用八通道微量量热仪、压汞仪、X射线衍射仪、扫描电子显微镜及能谱仪等分析手段,分析了m(M)/m(P)比值对磷酸镁水泥石自收缩的作用机理.结果表明,磷酸镁水泥石的自收缩呈现出3个阶段的特征,即早期的迅速收缩阶段、微膨胀阶段、收缩缓慢发展阶段.随着m(M)/m(P)比值的增大,由于磷酸镁水泥石的水化放热量降低,水泥石内部孔隙率增大,水化产物结晶度降低,水泥石结构疏松,所以,自收缩率减小.
关键词:
磷酸镁水泥
,
自收缩
,
m(M)/m(P)比值
