Experimental and theoretical identification of a high-pressure polymorph of Ga2S3 with α-Bi2Te3-type structure

Since the discovery of α-phase Bi2Te3, Sb2Te3, and Bi2Se3 as 3D topological insulators, many experimental and theoretical studies of A2B3-type chalcogenides have been performed to search for new materials with interesting elastic and electric properties at ambient and extreme conditions. In this study, high-pressure properties of Ga2S3 have been characterized by in situ synchrotron X-ray diffraction (XRD), X-ray absorption near edge structure measurements, and Density-functional theory (DFT) calculations. At ∼16.0 GPa, a phase transition of α′-Ga2S3 (Cc and Z = 4) is observed experimentally to a new polymorph, which is indentified to be the tetradymite-type or α-Bi2Te3-type crystal structure (R3¯m and Z = 3) by laser-annealing XRD experiments and DFT calculations. The isothermal pressure-volume relationship of Ga2S3 is well described by the second-order Birch-Murnaghan equation of state with K0 = 59(2) GPa and K0′ = 4 (fixed) for the α′-Ga2S3, and K0 = 91(3) GPa, and K0′ = 4 (fixed) for the tetradymite-type phase. In addition, band gap of α′-Ga2S3 decreases on compression and the tetradymite-type Ga2S3 exhibits metallization based on DFT calculations. The pressure-induced phase transition accompanying by changes of elastic and electrical properties may give some implications to other chalcogenides under high pressure.