Thermodynamic stability of various phases of zinc tin oxides from ab initio calculations

Thermodynamic stabilities of various phases in ZnO–SnO2 systems were investigated based on the Gibbs energy obtained from density functional theory (DFT) calculations. The pressure–temperature (p–T) phase diagram was determined; the coexistence of ZnO and SnO2 was the most stable phase in the low temperature region at zero external pressure, while Zn2SnO4 with the inverse spinel structure and ZnSnO3 with the lithium niobate structure were stable at the high temperature and high pressure region. Various octahedral configurations of the inverse spinel structures of Zn2SnO4 were considered. The calculated results showed feasible agreement with experimental data on the phase stability and explained well the experimental observation of the mixed state of Zn2SnO4, ZnO and SnO2 at mid-range temperatures and pressures. Considering the atomic structures, bulk moduli and thermodynamic stabilities, the local density approximation calculations were found to describe experimental observations more accurately than the generalized gradient approximation calculations. The phase transitions in the ZnO–SnO2 system were found to be dominated by the changes in both the Zn–O bond length and the coordination number of Zn, rather than changes in the bond length of Sn–O and the coordination number of Sn.