Facet-dependent electrical and mechanical properties of polyhedral Cu₂O under compression

In this paper, both the facet-dependent electrical properties and mechanical stability of submicron-sized polyhedral Cu₂O are investigated with in-situ resistivity measurements with pressure up to 25.0 GPa. The pressure-induced morphology changes are characterized by scanning/transmission electron microscopy. X-ray photoelectron spectroscopy measurements are also adopted to rationalize the diversity of the electrical resistivity of polyhedral Cu₂O under compression. The electrical properties of cubic, truncated octahedral, and octahedral Cu₂O show extremely different pressure dependence, which can be attributed to the preferential adsorption of oxygen on Cu₂O (111) facet. The anomalous changes in electrical resistivity at 0.7–2.2, 8.5, 10.3, and 21.6 GPa are due to pressure-induced structural phase transitions of the Cu₂O crystals. The dramatic reductions of resistivity in cubes and octahedras at 15.0 GPa and of truncated octahedras at 21.2 GPa are driven by pressure-induced crush and nanocrystallization of Cu₂O crystals. The mechanical stability of truncated octahedral Cu₂O is better than those of both cubic and octahedral Cu₂O. Our results not only elucidate the underlying mechanisms for understanding the two previously reported pressure-dependent electrical resistance change trends difference, but also give a reasonably explanation of the facet-dependent mechanical property of Cu₂O.