Electronic structure and phase equilibria in ternary substitutional alloys

Abstract

A reliable and consistent scheme for studying phase equilibria in ternary substitutional alloys based on the tight-binding approximation is presented. With the electronic parameters obtained from linear muffin-tin orbital calculations, we show that the computed densities of states and band structures compare well with those obtained from more accurate ab initio calculations. Disordered alloys are studied within the tight-binding coherent-potential approximation formalism extended to multi-component alloys. The energetics of ordered systems is obtained through effective-pair interactions computed with the general perturbation method. Finally, partially ordered alloys are studied with a novel simplification of the molecular coherent-potential approximation combined with the general perturbation method. The formalism is applied to the study of bcc-based ternary Zr - Ru - Pd alloys which are promising candidates for medical implant device applications. Using the energetics obtained with the aforementioned scheme, we apply the cluster-variation method to study phase equilibria for particular pseudo-binary alloys, and show that the results are consistent with the observed behaviour of the electronic specific heat coefficient with composition for the system.