Synthesis, crystal structure, and electronic structure of Ba₂GeTe₃(Te₂)

Black crystals of Ba₂GeTe₃(Te₂) were obtained by the “U-assisted” reaction of U, Ba, Ge, and Te at 1173 K using the sealed-tube method. The crystal structure of Ba₂GeTe₃(Te₂) was determined by a single crystal X-ray study at 100(2) K. It crystallizes in the space group Pnma of the orthorhombic crystal system with four formula units in a cell with constants a = 6.7900(14) Å, b = 23.720(5) Å, and c = 6.9300(14) Å. The crystal structure of Ba₂GeTe₃(Te₂) can be described as pseudo one-dimensional with zig-zag chains of ¹ _∞[GeTe₃ ²⁻] where each Ge atom is bonded to four Te atoms in a distorted tetrahedron. These chains are separated by the Ba²⁺ cations and homoatomic dimers of Te₂ ²⁻. Around each Ba atom there are nine Te atoms in a distorted tricapped trigonal prism. Charge balance in Ba₂GeTe₃(Te₂) is achieved with 2 × Ba²⁺, 1 × Ge⁴⁺, 3 × Te²⁻, and 1 × Te₂ ²⁻. Density functional theory (DFT) calculations suggest Ba₂GeTe₃(Te₂) is a metal with Ge- and Te-derived states contributing the most around the Fermi level.