Volume changes in binary alloy ordering, a binary classical density functional theory approach

TL;DR

This paper uses classical density functional theory to analyze volume changes during binary alloy ordering, focusing on lattice volume effects and vibrational entropy contributions.

Contribution

It introduces a tractable density functional approach to model volume changes in binary alloy ordering, incorporating vibrational entropy effects.

Findings

The model captures volume change effects in alloy ordering.

Additional entropy terms account for vibrational contributions.

The approach simplifies to a lattice gas formalism with extra interactions.

Abstract

The chemical ordering transition in a binary alloy is examined using classical density functional theory for a binary mixture. The ordered lattice is assumed to be obtained from the disordered lattice by a volume change only, as in L1_2 ordering from an face centered cubic chemically disordered crystal. Using the simplest possible approach, second order truncation of the expansion, non-overlapping Gaussian distributions at the sites, and expansion of the correlation functions about the sites, a very tractable expansion is obtained. Under these assumptions the expansion consists of the same terms as the lattice gas formalism where the lattice is implicitly taken as fixed, plus additional interaction terms, and an additional entropy term. This additional entropy term represents a lowest order approximation to the vibrational entropy change.