A Combined Theoretical and Experimental Study of the Pressure-induced Phase Transitions in GeSe

A recent study revealed that GeSe transforms into a new β phase under a hydrostatic pressure of 6 GPa [J. Am. Chem. Soc., 2017, 139 (7), pp 2771–2777]. In this work, we systematically investigate the pressure-induced phase transitions of GeSe up to 16 GPa by first-principles evolutionary structure searches. Two novel intermediate phases are found to exist at a pressure range in-between those of the existing α and β phases. We find that α-GeSe transforms into a rhombohedral phase with a space group of R3m (a GeTe prototype) at a small hydrostatic pressure. Laser-heated diamond anvil cell experiments were performed to provide further evidence of the existence of this R3m phase, which shows robust ferroelectricity in analogous to GeTe. By further increasing the external pressure, the R3m phase gradually transforms into a rock-salt phase. Based on electronic structure calculations from density functional theory and a tight-binding model, we show that this rock-salt phase is a topological crystalline insulator. The new phases presented in this work greatly enrich our knowledge of the high-pressure behaviors of GeSe.