Pbca-type In2O3: the lost pressure-induced post-corundum phase

TL;DR

This study clarifies the high-pressure phase transitions of In2O3, revealing a new post-corundum phase supported by experimental data and ab initio calculations, leading to a revision of sesquioxide phase diagrams.

Contribution

It identifies a previously unknown Rh2O3-III-type phase in In2O3 and demonstrates its stability as the post-corundum phase through combined experimental and theoretical analysis.

Findings

In2O3 transitions to Rh2O3-II structure under pressure.

Discovery of a new Rh2O3-III-type phase upon decompression.

Revised phase diagram for sesquioxides incorporating the new phase.

Abstract

Contradictory results of high-pressure studies in cubic bixbyite-type indium oxide (c-In2O3) at room temperature (RT) have motivated us to perform high-pressure powder x-ray diffraction and Raman scattering measurements in this material. On increasing pressure c-In2O3 undergoes a transition to the Rh2O3-II structure. On decreasing pressure Rh2O3-II-type In2O3 undergoes a transition to a previously unknown phase which is isostructural to Rh2O3-III. On further decrease of pressure, another phase transition to corundum-type In2O3, which is metastable at room conditions, is observed. Recompression of metastable corundum-type In2O3 shows that the Rh2O3-III phase is the post-corundum phase. Our results are supported by theoretical ab initio calculations which show that the Rh2O3-III phase could be present in other sesquioxides, thus leading to a revision of the pressure-temperature phase diagrams of sesquioxides.