Rh₂O₃(II)-type structures in Ga₂O₃ and In₂O₃ under high pressure: Experiment and theory

High-pressure transitions of Ga₂O₃ and In₂O₃ were examined by using a laser-heated diamond-anvil cell combined with in situ x-ray diffractometry at pressures up to 108 GPa and 20 GPa, respectively. To predict the transition pressure to high-pressure phases, first principles static lattice energy calculations based on the density functional theory were also performed. Rh₂O₃(II) phases were confirmed as post corundum phases for both Ga₂O₃ and In₂O₃ at about 37 GPa and 7 GPa, respectively. The transition pressures determined by high-pressure experiments are almost consistent with those by theoretical computations. In regard to the present sesquioxides, a link of transition from corundum to perovskite was not confirmed. The Rh₂O₃(II) phases converted to corundum phases under decompression at room temperature. The bulk modulus of Rh₂O₃(II) phase in Ga₂O₃ and In₂O₃ were determined as 271±10 GPa and 169±4 GPa with their pressure derivatives fixed at 4, respectively.