Pressure-induced stable structures and physical properties of Sr–Ge system

Abstract

We have systematically investigated the structures of Sr–Ge system under pressures up to 200 GPa and found six stable stoichiometric structures, they being Sr3Ge, Sr2Ge, SrGe, SrGe2, SrGe3, and SrGe4. We demonstrate the interesting structure evolution behaviors in Sr–Ge system with the increase of germanium content, Ge atoms arranging into isolated anions in Sr3Ge, chains in Sr2Ge, square units in SrGe, trigonal units and hexahedrons in SrGe2, cages in SrGe3, hexagons and Ge8 rings in SrGe4. The structural diversity produces various manifestations of electronic structures, which is of benefit to electrical transportation. Among them, these novel phases with metallic structures show superconductivity (maximum T c ∼ 8.94 K for Pmmn Sr3Ge). Notably, the n-type semiconducting Pnma SrGe2 structure exhibits high Seebeck coefficient and excellent electrical conductivity along the y direction, leading to a high ZT value up to 1.55 at 500 K, which can be potential candidates as high-performance thermoelectrics. Our results will enable the development of fundamental science in condensed matter physics and potential applications in novel electronics or thermoelectric materials.