Pbca-Type In2O3: The High-Pressure Post-Corundum phase at Room Temperature.

High-pressure powder X-ray diffraction and Raman scattering measurements in cubic bixbyite-type indium oxide (c-In2O3) have been performed at room temperature. On increasing pressure c-In2O3 undergoes a transition to the Rh2O3–II structure but on decreasing pressure Rh2O3–II-type In2O3 undergoes a transition to a previously unknown phase with Pbca space group which is isostructural to Rh2O3–III. On further decrease of pressure, we observed a phase transition to the metastable corundum-type In2O3 near room conditions. Recompression of the metastable corundum-type In2O3 at room temperature leads to a transition to the Rh2O3–III phase, thus showing that the Rh2O3–III phase is the post-corundum phase at room temperature. Our results are supported by theoretical ab initio calculations. Furthermore, they show that the Rh2O3–III phase could be present in other sesquioxides, thus prompting to a revision of the pressure–temperature phase diagrams of sesquioxides