Post-perovskite phase in selected sesquioxides from density-functional calculations

We search for the existence of the post-perovskite structure in several nonmagnetic ${M}_{2}{\mathrm{O}}_{3}$ sesquioxides using density-functional calculations. For each material we consider the corundum, ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}$-type II, perovskite, and post-perovskite structures. The perovskite structure is unstable with respect to at least one of the other structures at all pressures for all materials. The post-perovskite structure is stable above $120\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ in ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, above $344\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ in ${\mathrm{Rh}}_{2}{\mathrm{O}}_{3}$, above $136\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ in ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$, and above $47\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ in ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$.