Preparation and structure of a new germanium clathrate, Ba24Ge100

Single crystals of a new germanium clathrate, Ba24Ge100, were synthesized by the Czochralsky pulling method using a tetra-are furnace under an Ar atmosphere. The crystal structure was studied by X-ray single-crystal analysis. The clathrate crystallized in the cubic space group P4(1)32 with a = 14.5635(7) Angstrom, V = 3088.9(2) Angstrom(3). The final refinement using 903 unique reflections converged at R = 0.032 and R-w = 0.036. In the structure, germanium atoms are linked by sp(3) sigma-bonds to form a three-dimensional network, in which barium atoms are enclosed. There are three sites for the barium atoms having different coordination environments. One site is in a Ge-20 dodecahedron and the others are coordinated with 20 Ge atoms and 8 Ge atoms, respectively. (C) 2000 Academic Press.