Mitsuhiro Asato1 and Toshiharu Hoshino2
1Graduate School of Electronic Science and Technology, Shizuoka University, Hamamatsu 432-8561
The impurity-impurity (X-X; X=Ti-Cu, Zr-Ag) interaction energies, from 1st-neighbor to 8th-beighbor, in metals (Cu, Ni, Ag, Pd), are calculated as accurately as the lattice parameters and bulk moduli of complete metals [Materia Japan, 37(1998), 564], based on the Korringa-Kohn-Rostoker Green's function method for point defects [in Computational Physics as a New Frontier in Condensed Matter Research, ed. by H. Takayama et al., Physical Society of Japan, Tokyo, (1995), 105-113], using density functional theory. We use the local-spin-density approximation (LSDA) and the generalized-gradient approximation (GGA) of Perdew and Wang [in Electronic Structure of Solids '91, ed. by P. Zieche et al., Academic Verlag, Berlin, (1991), 11-20 ]. First we review the present status of the first-principles calculations for metals; the GGA calculations correct very well the deficiencies of the LSDA for metals, i.e. the underestimation of equilibrium lattice parameters and the overestimation of bulk moduli. Secondly we show that the fundamental differences among segregation, solid solution, and ordering behavior of the binary alloys of impurity and host elements considered here, known experimentally, may be distinguished very well by use of the present impurity-impurity interaction energies. It should be noted that the observed ordering behavior of NiX (X=Mn, Fe, Co) may not be reproduced without the spin-polarization effect. The importance of magnetism in Ni-based alloys is quantitatively discussed by comparing with the calculated results for non-magnetic Pd-based alloys. Finally we show that the temperature dependence for the solid solubility limit of impurities in metals, such as Rh in Pd and Ru in Pd (PdRh and PdRu are segregated at low temperatures and become disordered at high temperatures), may be reproduced very accurately by the cluster variation method based on the present impurity-impurity interaction energies. We also found that the inclusion of the far-neighbor interaction energies is very important.
(Received December 22, 1998; In Final Form March 17, 1999)
impurity-impurity interaction energy, phase diagram, solid solubility limit of impurities in metal, Korringa-Kohn-Rostoker-green's function method for point defects, density functional theory, local-spin-density approximation, generalized-gradient approximation, cluster variation method
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