Pressure-induced first order phase transition in bulk GeSe

The phase transition mechanism in germanium selenide (GeSe) from the rhombohedral to face-centered cubic (FCC) phase is extensively analysed using density functional theory (DFT). The energy profile of GeSe reveals that the rhombohedral structure lies at the minimum energy, and the enthalpy differences predict its transition to the FCC phase at 7.3 GPa. Furthermore, we confirm the phase transition by calculating the phonon dispersion curves at various pressures. The rhombohedral phase of GeSe is dynamically stable at 0 GPa, whereas the FCC phase shows stability at 7.3 GPa. The rhombohedral to FCC phase transition is scrutinized by the degeneracy and splitting of the phonon modes along with the components of Born effective charge and dielectric constant. Investigation of the lattice transport properties of GeSe in both phases shows that FCC possesses high thermal conductivity (8.06 W/m K) as compared to the rhombohedral phase (4.88 W/m K) due to the three phonon emission process for scattering channels. The electronic band structure of the FCC GeSe under pressure shows its topological nature, and similar behavior was observed in the rhombohedral phase at 7.3 GPa. The rhombohedral phase of GeSe manifests better thermoelectric performance at 0 GPa with the thermoelectric figure of merit of 0.82 at 300 k much higher than its FCC phase at 7.3 GPa, suggesting its application in thermoelectric energy conversion.