New insights on the $\mathrm{GeSe_{x}Te_{1− x}}$ phase diagram from theory and experiment

The high-pressure and low-temperature behaviour of the $\mathrm{GeSe_{x}Te_{1− x}}$ xsystem (x= 0, 0.2, 0.5, 0.75, 1) was studied using a combination of powder diffractionmeasurements and first-principles calculations. Compounds in the stability fieldof the GeTe structure type (x= 0, 0.2, 0.5) follow the high-pressure transitionpathway: GeTe-I (R3m)->GeTe-II (f.c.c.)->GeTe-III (Pnma). The newlydetermined GeTe-III structure is isostructural to-GeSe, a high-pressure andhigh-temperature polymorph of GeSe. Pressure-dependent formation enthalpies and stability regimes of the $\mathrm{GeSe_{x}Te_{1− x}}$ 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-Geinteractions is elucidated using the crystal orbital Hamilton population method.Finally, a sketch of the high-pressure phase diagram of the system is provided