The Influence of Quasi-Particle Lifetimes and Electronic Topological Transitions on the Deviations from Vegard’s Rule in AG-PD Alloys

Abstract

In this paper, we discuss about the variations of the equilibrium lattice parameter versus the alloy concentration in AgPd fcc solid solutions. We interpret the experimentally observed deviations from Vegard’s rule in terms of the Electronic Topological Transition (ETT) related to the d band filling which occurs about the equiatomic concentration. Through simple Rigid Band Model (RBM) calculations, we show how the finiteness of quasi-particle lifetimes affects these deviations, namely reducing their amplitude. RBM calculations are also used to compare versus the experiment the predictions of ab initio Local Density Approximation, Korringa-Kohn-Rostoker Coherent Potential Approximation (LDA-KKR-CPA) calculations. On this basis we shall discuss the apparent underestimation of the relevant quasi-particle lifetime in the CPA theory.