High-pressure study of theβ-to-αtransition inGa2O3

Abstract

The high-pressure behavior of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ is studied up to $40\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ using synchrotron x-ray diffraction and Raman spectroscopy in diamond anvil cells. A phase transformation from the monoclinic $\ensuremath{\beta}$-phase $(C2∕m)$ is observed at a pressure above 20--$22\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The high-pressure polymorph is identified as the $\ensuremath{\alpha}$-phase that is isostructural with corundum ($R\overline{3}c$ symmetry) from the x-ray diffraction data. However, considerable anion disorder is indicated by the appearance of broad bands in the Raman spectra. The experimental results are complemented by ab initio theoretical calculations of the energetics of the two structures and the lattice dynamics.