Phase equilibrium of Cd _{1– x} Zn _x S alloys studied by first-principles calculations and Monte Carlo simulations

Abstract

The first-principles calculations based on density functional theory combined with cluster expansion techniques and Monte Carlo (MC) simulations were used to study the phase diagrams of both wurtzite (WZ) and zinc-blende (ZB) Cd 1−x Zn x S alloys. All formation energies are positive for WZ and ZB Cd 1−x Zn x S alloys, which means that the Cd 1−x Zn x S alloys are unstable and have a tendency to phase separation. For WZ and ZB Cd 1−x Zn x S alloys, the consolute temperatures are 655 K and 604 K, respectively, and they both have an asymmetric miscibility gap. We obtained the spatial distributions of Cd and Zn atoms in WZ and ZB Cd 0.5 Zn 0.5 S alloys at different temperatures by MC simulations. We found that both WZ and ZB phases of Cd 0.5 Zn 0.5 S alloy exhibit phase segregation of Cd and Zn atoms at low temperature, which is consistent with the phase diagrams.