CRYSTAL-STRUCTURE AND PROPERTIES OF TLCU6S4

The structure of TlCu6S4 has been determined from single-crystal X-ray diffraction data, confirming (RF = 0.061, RwF = 0.059) a previous structure hypothesis that the compound is the third member of a structure series TlCu2nSn+1. The compound is tetragonal (space group I4/mmm, no. 139; Z = 2) with the cell parameters a = 3.9465 A ̊, c = 24.230 A for nearly stoichiometric material. The investigated crystal was copper deficient, corresponding to the formula TlCu5.5S4 and to the cell parameters a = 3.9357 A ̊, c = 24.183 A ̊. Like the previous members of the series, this compound has metallic conduction owing to a high concentration of valence band holes. All the members of the series are layer structures with tetragonal symmetry, derived from anti-fluorite-type Cu2S with thallium layers interfoiling slabs with copper in tetrahedral voids of the sulphur lattice. © 1990.