Phase Relations in the SrO-IrO₂-Ir System in Air

The equilibrium phase relations for the SrO-IrO₂-Ir system were determined in an air environment at atmospheric pressure. A ternary equilibrium phase diagram was constructed indicating selected oxygen reaction lines and tie lines. A binary representation is given for the ternary system in air. Of the nine phases detected in this study, three are stable and six are probably metastable under atmospheric conditions. The stable compounds, 4SrO · IrO₂, 2SrO · IrO₂, and SrO · IrO₂ dissociate at 1540, 1445, and 1205 °C, respectively. The metastable phases include low-4SrO · IrO₂, 2SrO · 3IrO₂, xSrO · IrO₂(x > 2), ySrO · IrO₂(4 > y > 2), zSrO · IrO₂(2 > z > 1), and 3SrO · 2IrO₂. The specific composition of the metastable phases could not be ascertained with certainty. The x-ray patterns of all phases detected in this study were indexed with the exception of that of the zSrO · IrO₂(2 > z > 1) compound. A summary of x-ray data is given for all known phases occurring in the system.