Phase equilibrium of Cd1–xZnxS alloys studied by first-principles calculations and Monte Carlo simulations*

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) Cd1-xZnxS alloys. All formation energies are positive for WZ and ZB Cd1-xZnxS alloys, which means that the Cd1-xZnxS alloys are unstable and have a tendency to phase separation. For WZ and ZB Cd1-xZnxS 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 Cd0.5Zn0.5S alloys at different temperatures by MC simulations. We found that both WZ and ZB phases of Cd0.5Zn0.5S alloy exhibit phase segregation of Cd and Zn atoms at low temperature, which is consistent with the phase diagrams.