Unraveling a novel ferroelectric GeSe phase and its transformation into a topological crystalline insulator under high pressure

Abstract

Germanium selenide is a promising material for electronic, photovoltaic, and thermoelectric applications; however, structural phase transitions of GeSe under pressure are controversial. Combining evolutionary algorithms, density functional theory, tight-binding method, and laser-heated diamond anvil cell experiments, pressure-induced phase transitions of GeSe are thoroughly investigated. Two novel intermediate phases are predicted to exist in between the well-known α-GeSe and the recently discovered β-GeSe under high pressure. α-GeSe is found to transform into a rhombohedral crystal structure with a space group of R3m at a low hydrostatic pressure. The R3m phase of GeSe exhibits robust ferroelectricity analogous to GeTe. By further increasing the pressure to approximately 6 GPa, the R3m phase is predicted to transform into a rock-salt structure, becoming a 3D topological crystalline insulator with an inverted band structure. The newly discovered GeSe high-pressure phases greatly enrich our knowledge of IV–VI compounds. The atoms in germanium selenide can adopt more configurations than previously thought according to a study by researchers in China. A phase change, the rearrangement of atoms in a solid from one crystal structure to another, can radically alter a material’s properties. Such a change in phase can be induced by exposing matter to high pressure. Kuo Li from the Center for High Pressure Science and Technology Advanced Research in Beijing, Yue Chen from The University of Hong Kong, and their co-workers have combined multiple computational and experimental techniques to identify the phases of germanium selenide, a material useful for energy conversion. Recently a high-pressure phase called β-GeSe was discovered in addition to the common low-pressure α-GeSe phase. The researchers predict two further phases at intermediate pressure, each with its own distinctive electrical properties. Pressure-induced phase transitions in GeSe are investigated from theory and experiment. Two new phases are predicted to exist in-between the well-known α-GeSe and the recently discovered β-GeSe under pressures. It is predicted that α-GeSe transforms into a rhombohedral structure with a space group of R3m and exhibits robust ferroelectricity at a low hydrostatic pressure. Laser-heated DAC experiments have been conducted to provide further evidence on the existence of the R3m phase. By increasing the hydrostatic pressure to approximately 6 GPa, the R3m phase is predicted to transform into a rock-salt crystal structure ( $$Fm\bar 3m$$ ) and become a topological crystalline insulator.