New insights on the GeSe x Te 1− x phase diagram from theory and experiment

The high-pressure and low-temperature behaviour of the GeSe x Te 1− x system ( x = 0, 0.2, 0.5, 0.75, 1) was studied using a combination of powder diffraction measurements and first-principles calculations. Compounds in the stability field of the GeTe structure type ( x = 0, 0.2, 0.5) follow the high-pressure transition pathway: GeTe-I ( R 3 m ) → GeTe-II (f.c.c.) → GeTe-III ( Pnma ). The newly determined GeTe-III structure is isostructural to β-GeSe, a high-pressure and high-temperature polymorph of GeSe. Pressure-dependent formation enthalpies and stability regimes of the GeSe x Te 1− x polymorphs were studied by DFT calculations. Hexagonal Ge 4 Se 3 Te is stable up to at least 25 GPa. Significant differences in the high-pressure and low-temperature behaviour of the GeTe-type structures and the hexagonal phase are highlighted. The role of Ge...Ge interactions is elucidated using the crystal orbital Hamilton population method. Finally, a sketch of the high-pressure phase diagram of the system is provided.