High Pressure-Induced Phase Transition In $\beta $-Ga$_{2}$O$_{3}$: in situ Synchrotron X-Ray Diffraction Studies up to 70 Gpa*

A renewed interest in $\beta $-Ga$_{2}$O$_{3}$ has arisen since it has potential applications in optoelectronic devices. We performed \textit{in situ} synchrotron radiation x-ray diffraction studies in a diamond anvil cell on $\beta $-Ga$_{2}$O$_{3}$ on compression up to 70 GPa and on successive decompression. The pressure-evolution of x-ray diffraction patterns was consistent with a low-to-high density phase transition. A thermodynamically stable \textit{$\beta $}-Ga$_{2}$0$_{3}$ phase was converted into the \textit{$\alpha $}-Ga$_{2}$0$_{3}$ phase, which is unstable at ambient conditions. The effect of hydrostatic and non-hydrostatic compression conditions on the evolution of the phase transition was also investigated in compression and decompression cycles. This work is the first report of high-pressure investigations of Ga$_{2}$O$_{3}$ on compression up to 70 GPa.