Characterization of phase transition on Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ induced by shock-recovery experiment

Shock recovery experiments on Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ sample were carried out by the impact of a flyer plate accelerated by a single-stage powder-propellant gun. A sintered pellet and a single crystalline plate of Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ were used. Sample was encapsulated in copper container. The recovered samples were characterized by X-ray diffraction (XRD) analysis and Raman spectroscopy. The recovered single crystalline sample was reduced to grains. Analysis of the shocked samples suggests that the onset pressure for the transition from the $\beta $- to $\alpha $-Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ phase lies between 11 and 16 GPa. For the sample shocked at 20 GPa, most of Raman spectra were corresponding to $\beta $-Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ phase and the Raman spectra obtained from some of the grains that recovered from shock compression agreed with the $\alpha $-Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ phase. The XRD pattern consisted of a mixture of $\beta $- and $\alpha $-Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ phases. Although Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ exists five forms of crystal structure under ambient condition, all other structures except for $\beta $- and $\alpha $-Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ were not observed.