The phase boundary of the β-α transition in Ga2O3 under high temperature and high pressure

In this study, we reexamined the behavior of β-Ga2O3 in diamond anvil cell at room temperature under pressures up to 80.86 GPa using in situ high-pressure Raman scattering and angle-dispersive synchrotron radiation X-ray diffraction techniques. Argon was used as a quasi-hydrostatic pressure-transmitting medium. The phase transition from low-density β-Ga2O3 to high-density α-Ga2O3 was observed, beginning at approximately 20.57 GPa and completing in the pressure range of 39.70–42.29 GPa. The α-Ga2O3 phase remains stable up to approximately 80 GPa at ambient temperature, and the β-to-α phase transition is an irreversible reconstructive phase transition. A third-order Birch-Murnaghan equation of state fit to the unit-cell volume as a function of pressure yielded a zero-pressure bulk modulus B0 of 200.2(22) GPa for β-Ga2O3, with a pressure derivative B0′ of 3.0(11) GPa. For α-Ga2O3, the fit gave B0 = 354.8(43) GPa and B0′= 2.2(8) GPa. When B0′ was fixed at 4, a re-fit of the experimental data provided B0 = 267.9(7) GPa for the α-phase, which is higher than B0 = 182.6(7) GPa for the β-phase, indicating that α-Ga2O3 exhibits greater resistance to compression. Based on high-pressure experimental results for β-Ga2O3 at different temperatures, the phase boundary for the β-to-α transition, exhibiting a negative Clapeyron slope, is presented in this study. With increasing temperature, the onset pressure of the β-to-α transition gradually decreases, and the phase transition hysteresis effect weakens.