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.

Key Words:

• Resistivity
• compressibility
• phase diagram
• copper oxides
• silver oxides