THE ORIGINS OF PHASE-STABILITY IN ORDERED AND DISORDERED NI-PT ALLOYS

Using the atomic-sphere approximation formulation of the Korringa-Kohn -Rostoker coherent potential approximation (KKR CPA) method, we have s tudied the effects of relativity on the electronic structure of ordere d and substitutionally disordered Ni-Pt alloys. The inclusion of mass- velocity and Darwin terms are found to be essential for describing the experimentally observed ground-state properties. For the stability of disordered Ni-Pt alloys we find that, in addition to relativity, the minimization of charge-transfer effects are important. We also find th at the treatment of ordering tendencies based on the band energy term alone is not sufficiently accurate for alloys with charge-transfer eff ects. Further analysis, in terms of basis functions, densities of stat es and non-spherically averaged charge densities, indicate the importa nce of s- and d-electrons of Pt for the stability of both ordered and disordered Ni-Pt alloys.