Concentration and Temperature Dependent Effective Cluster Interactions in Substituting Disordered Alloys

摘要

We discuss methods which allow the determination of unique concentration dependent effective cluster interactions (ECI's) in substitutional alloys. These methods are based on the coherent potential approximation (CPA) and on the representation of the configuration dependent part of the disorder energy in terms of ECI's. Two schemes proposed for calculating ECI's within the CPA framework, the generalized perturbation method (GPM) and the embedded cluster method (ECM) are compared with one another and with the method proposed by Connolly and Williams, both formally and by means of calculations. It is found that the GPM and the ECM are conceptually and numerically quite similar, the ECM corresponding to a complete summation of certain terms in the GPM expansion. Both these methods lead to unique values of ECI's for a large class of substitutional alloys, particularly strong-scattering alloys such as those involving transition metals. The Connolly-Williams approach, on the other hand, yields ECI's depending on the size of the cluster used in the fitting procedure, and thus to nonunique predictions of phase stability. The use of the GPM/ECM in calculating most stable ordered structures at T = 0K is illustrated in terms of Pd V and Pd Rh alloys, and the possible use of these methods in constructing alloy phase diagrams is briefly discussed. 23 refs., 9 figs., 1 tab. (ERA citation 14:006179)