Crystal Structure Built from a GeO₆–GeO₅ Polyhedra Network with High Thermal Stability: β–SrGe₂O₅

By tackling the challenge of extending transparent oxide semiconductors to Ge-based oxides, we have found a not-yet-reported crystal structure, named β-SrGe2O5, which is composed of edge-sharing GeO6 octahedra interconnected by GeO5 bipyramids. Single crystals were successfully grown by the high-pressure flux method. β-SrGe2O5 has a band gap of 5.2 eV and a dispersive conduction band with an effective mass as small as 0.34 times the electron rest mass, which originates from the edge-sharing GeO6 octahedra network. Although known compounds with octahedral GeO6 coordination are commonly unstable at atmospheric pressure and elevated temperatures, β-SrGe2O5 exhibits thermal stability up to 700 °C.