First-principles calculations of the thermodynamics of wurtzite and zincblende ZnO1-xSx alloys

A theoretical study on the thermodynamics of wurtzite (WZ) and zincblende (ZB) ZnO1-xSx was carried out using the first-principles method and the cluster expansion method. The effective cluster interaction of the cluster expansion was calculated, which constructs the formation energy of the disordered alloys. Excluding the contribution of lattice vibrations, the critical temperature of phase separation for the WZ structure is 3946 K and for the ZB structure is 3894 K. Including lattice vibrations, a reduction of the critical temperature by 17.1% was found for the WZ structure, thus increasing the solid solubility of WZ-ZnO1-xSx. In contrast, an increase of the critical temperature by 4.4% was found for the ZB structure when considering lattice vibrations. With analyses of the formation energy and phase diagram, the ZB structure was found thermodynamically more stable than the WZ structure at high temperatures.