Phase equilibria in the pseudo-binary In₂O₃–SnO₂ system

The pseudo-binary In₂O₃–SnO₂ phase diagram has been determined in the range of 1000–1650 °C using electron probe microanalysis (EPMA) and x-ray diffraction (XRD) analysis of solid-state sintered samples. The solubility of SnO₂ in In₂O₃ was found to range from 1.3 mol% at 1000 °C to a maximum of 13.1 mol% at 1650 °C, indicating that commercial SnO₂-doped In₂O₃ thin films are thermodynamically metastable. In₂O₃ was found to have negligible solubility in SnO₂ throughout the temperatures examined. In this study two intermediate compounds, In₄Sn₃O₁₂ and In₂SnO_5, were found. Each phase was found to be stable only at high temperatures, decomposing eutectoidally at 1325 and 1575 °C, respectively. This is believed to be the first report of the high temperature phase In₂SnO₅, which is attractive for future research as a transparent conducting oxide.