  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.
