Unexpected High-Pressure Phase of GeTe with an Origin of Low Ionicity and Electron Delocalization

First-principles evolutionary searches have been performed to systematically explore the high-pressure phases of germanium telluride. Two new phases are found to be both energetically and dynamically stable under moderate pressures. A Pnma orthorhombic phase with an uncommon “boat” conformation and a P4/nmm tetragonal phase are found to become stable at ∼15 and ∼37 GPa, respectively. The long-believed high-pressure B2 phase, however, is found to be energetically unfavorable comparing to the P4/nmm phase. Our calculations of the electronic structures show that Pnma-boat GeTe and P4/nmm GeTe exhibit semimetallic and metallic behaviors, respectively. On the basis of the electron–phonon coupling calculations, P4/nmm GeTe is shown to have a superconducting transition at low temperatures, resulting from its sudden decrease of ionicity and the more delocalized lone-pair electrons. The discovery of these new GeTe phases further enriches our knowledge of the high-pressure behaviors of the IV–VI compounds.