Papers by Keyword: Coherent Potential Approximation

Abstract: A method for electronic structure calculations of strongly correlated materials based on the coherent potential approximation is formulated and implemented. The evolution of the electronic structure of the LaMnO perovskite system in dependence on oxygen deficiency is studied.

Abstract: X-ray photoelectron spectra of TiO₂:Fe are measured. Electronic structure and magnetic properties of rutile doped by iron are calculated in frames of the coherent potential approximation. The main experimental spectral features of TiO₂:Fe such as heterovalent cation substitution (Fe³⁺→Ti⁴⁺), decreasing of the band gap value and appearance of additional features at the bottom and top of X-ray photoelectron spectra of valence band in comparison with those for undoped TiO₂ are described.

Abstract: The thermodynamic properties and phase transformations of metals and alloys are studied using the statistical moment method, going beyond the quasi-harmonic approximations. Including the power moments of the atomic displacements up to the fourth order, the Helmholtz free energies and the related thermodynamic quantities are derived explicitly in closed analytic forms. The thermodynamic quantities, like thermal lattice expansion coefficients, specific heats, Grüneisen constants, elastic constants calculated by using the SMM are compared with those of other theoretical schemes and the experimental results. The hcp-bcc structural phase transformations observed for IVB elements, Ti, Zr and Hf, are discussed in terms of the anharmonicity of thermal lattice vibrations. The equilibrium phase diagrams are calculated for the refractory Ta-W and Mo-Ta bcc alloys. In addition, the temperature dependence of the elastic moduli C11, C12 and C14 and those of the ideal tensile and shear strengths of the bcc elements Mo, Ta and W are studied: We also discuss the melting transitions of metals and alloys within the framework of the SMM and estimate the melting temperatures through the limiting temperature of the crystalline stability.

Abstract: The thermodynamic properties of high temperature metals and alloys are studied using the statistical moment method, going beyond the quasi-harmonic approximations. Including the power moments of the atomic displacements up to the fourth order, the Helmholtz free energies and the related thermodynamic quantities are derived explicitly in closed analytic forms. The configurational entropy term is taken into account by using the tetrahedron cluster approximation of the cluster variation method (CVM). The energetics of the binary (Ta-W and Mo-Ta) alloys are treated within the framework of the first-principles TB-LMTO (tight-binding linear muffin tin orbital) method coupled to CPA (coherent potential approximation) and GPM (generalized perturbation method). The equilibrium phase diagrams are calculated for the refractory Ta-W and Mo-Ta bcc alloys.