Pressure-induced structural and electronic phase transitions in GaGeTe

Chalcogenide-based compounds are an important part of the family of layered materials, extensively studied for their two-dimensional properties. An interesting line of investigation relates to the evolution of their properties with hydrostatic pressure, which could lead to structural transitions and itinerant electronic behavior. Here, we investigate the evolution of a layered ternary compound GaGeTe as a function of pressure with x-ray diffraction, Raman and infrared spectroscopy, and ab initio calculations. The Ge layer retains a germanenelike vibration though enveloped in Ga and Te layers. We show experimental and theoretical evidence of metallization in two steps. At -6 GPa Raman and infrared spectroscopic data undergo changes compatible with delocalized charge carriers. Calculations ascribe this to the Fermi-level crossing of a valence band. At -16 GPa infrared transmission and Raman modes disappear and x-ray diffraction signals a structural transition to a phase which is metallic according to our calculations. We obtain consistent agreement between experiment and theory concerning the structural, vibrational, and electronic structure evolution with pressure.