Pbca -Type In 2 O 3 : 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-In 2 O 3 ) have been performed at room temperature. On increasing pressure c-In 2 O 3 undergoes a transition to the Rh 2 O 3 –II structure but on decreasing pressure Rh 2 O 3 –II-type In 2 O 3 undergoes a transition to a previously unknown phase with Pbca space group which is isostructural to Rh 2 O 3 –III. On further decrease of pressure, we observed a phase transition to the metastable corundum-type In 2 O 3 near room conditions. Recompression of the metastable corundum-type In 2 O 3 at room temperature leads to a transition to the Rh 2 O 3 –III phase, thus showing that the Rh 2 O 3 –III phase is the post-corundum phase at room temperature. Our results are supported by theoretical ab initio calculations. Furthermore, they show that the Rh 2 O 3 –III phase could be present in other sesquioxides, thus prompting to a revision of the pressure–temperature phase diagrams of sesquioxides