Phonon modes and vibrational entropy of disordered alloys with short-range order: A first-principles calculation

Abstract

There has been increasing evidence about the effects of short-range order (or local chemical environment effects) on the lattice dynamics of alloys, which eventually affect the vibrational entropy difference among various phases of a compound, and hence their relative stability. In this article, we present an ab initio calculation of the lattice dynamics and the vibrational entropy of disordered systems with short-range order. The features in the phonon density of states were found to change systematically with chemical short-range order in the alloy. Plausible explanations for our smaller value of vibrational entropy of mixing compared to experiment are given in some detail. A general trend of the magnitude of vibrational entropy of mixing is explained by making a connection to the phonon lifetime broadening, an intrinsic property of any multiple scattering phenomenon. We illustrate the method by applying it to a body-centered cubic Fe1−xCrx alloy