Vacancy-mediated suppression of phase separation in a model two-dimensional surface alloy by the difference of the atomic jump rates

TL;DR

This study uses a vacancy-mediated diffusion model to analyze how the ratio of atomic jump rates affects phase separation in a two-dimensional alloy, revealing that a high jump rate ratio suppresses phase separation.

Contribution

It introduces a model linking atomic jump rate ratios to phase separation suppression in surface alloys, highlighting the role of vacancy-mediated diffusion.

Findings

High jump rate ratio ($\

) suppresses phase separation.

Small jump rate ratios lead to mild phase separation, not complete suppression.

Abstract

A vacancy-mediated collective diffusion model is used to compute a thermally-induced (spinodal) phase separation in a typical fcc bi-metallic surface alloy at low median concentration of vacancies, focusing on the effect of the ratio, $\Gamma=\Gamma_A/\Gamma_B$, of the jump rates to the vacant sites of the two types of atoms. The model is formulated for the diffusion of one atomic species and vacancies, employing the kinetic transport coefficients derived by Moleko \emph{et al.} (Phil. Mag. A 59, 141 (1989)). It is demonstrated that for A$_{0.7}$B$_{0.3}$ alloy, $\Gamma \sim 50$ results in suppression of phase separation, whereas very small $\Gamma$ values result in mild phase separation (i.e., the suppression is incomplete).