Stability of the cuprite-type structure at elevated pressures and temperatures

Abstract
Cu2O and Ag2O are the only two common materials which share the cubic cuprite structure, Strukturbericht type C3, h3m. We have studied the behavior of copper and silver oxides at elevated temperature and pressure, viz., by resistivity (to 6.5 GPa at 25°C), volume compressibility (< 2.6 GPa at 25°C), X-ray compressibility (to 6.3 GPa at 25°C), and by high pressure high temperature quenching experiments (to 6.0 GPa and 2000°C). Both Cu2O and Ag2O exhibit discontinuities in their resistivity at elevated pressures, suggestive of changes in crystallographic or electronic structure. Ag2O decomposes at pressures below about 3 GPa for temperatures above about 1100°C; it transforms into the layered C6 (CdI2-type) structure at pressures and temperatures higher than this. Above 5 GPa at 500°C Cu2O disproportionates into CuO and Cu. The results of this investigation are compiled with critical analyses of previous work, and are summarized in appropriate P-T phase diagrams.

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