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

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, $\mathrm{\Gamma }={\mathrm{\Gamma }}_A\mathrm{/}{\mathrm{\Gamma }}_B$, 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, $\mathrm{\Gamma }\sim 50$ results in suppression of phase separation, whereas very small $\mathrm{\Gamma }$ values result in mild phase separation (i.e., the suppression is incomplete).