Cluster variation method analysis of correlations and entropy in BCC solid solutions

TL;DR

This paper uses the cluster variation method combined with density functional theory to analyze correlations and entropy in BCC solid solutions, revealing different ordering behaviors and phase transitions in CuZn and AlLi compounds.

Contribution

It introduces a combined approach of cluster variation method and DFT to study ordering and entropy in BCC solid solutions, highlighting contrasting behaviors in specific compounds.

Findings

CuZn undergoes an order-disorder transition to CsCl structure

AlLi adopts NaTl structure without transition

Temperature-dependent correlations and entropies are evaluated

Abstract

Solid solutions occur when multiple chemical species share sites of a common crystal lattice. Although the single site occupation is random, chemical interaction preferences bias the occupation probabilities of neighboring sites, and this bias reduced the entropy of mixing below its ideal value. Sufficiently strong bias leads to symmetry-breaking phase transitions. We apply the cluster variation method to explore solid solutions on body centered cubic lattices in the context of two specific compounds that exhibit opposite ordering trends. Employing density functional theory to model the energetics, we show that CuZn exhibits an order-disorder transition to the CsCl prototype structure, while AlLi instead takes the NaTl prototype structure, and we evaluate their temperature-dependent order parameters, correlations and entropies.