CRYSTAL-STRUCTURE AND TWINNING OF KCD4GA5S12 AND SOME ISOTYPIC AB4C5X12 COMPOUNDS

Nine new compounds of composition AB4C5X12 with distinct elements being among A: K, Rb, Cs; B: Zn, Cd; C: Ga; X: S, Se, Te were prepared by solving ZnGa2S4, CdGa2S4, ZnGa2Se4, CdGa2Se4, and CdGa2Te4 in KBr, RbBr, and CsBr, respectively. The crystal structure of KCd4Ga5S12 was solved and refined to R = 0.03. It crystallizes with space group R3, the hexagonal lattice parameters being a0 = 13.782(3) angstrom and c0 = 9.330(3) angstrom [rhombohedral setting: a0 = 8.543(2) angstrom, alpha = 107.53(1)-degrees], and shows a thirteenfold superstructure. KCd4Ga5S12 consists of a cubic close packing of sulfur atoms with partially ordered Cd and Ga cations in the tetrahedral interstices. The potassium ion substitutes one sulfur atom and is located inside a cubooctahedral interstice of the sulfur sublattice. Frequently, twinning is observed which leads to a weighted coincidence site lattice in reciprocal space.