THE LAYERED COMPOSITE CRYSTAL-STRUCTURE OF THE TERNARY SULFIDE, (BIS)1.07TAS2 BITAS3

The crystal structure of a new type of ternary sulfide with a layered composite crystal structure, (BiS)1.07TaS2 was studied by the single crystal X-Tay diffraction method. The precession photograph of (BiS)1.07TaS2 revealed the composite diffraction patterns of BiS subsystem and TaS2 subsystem. The commensurate superlattice reflections of the BiS subsystem were observed together with the main diffractions of the TaS2 subsystem. The commensurate superlattice reflections of the BiS subsystem, which were not observed for other MS subsystems in (MS)(n)TaS2 (M = Pb, Sn, rare earth metals) are well indexed on the basis of the superstructure with a = 5.732(4) angstrom, b = 15.368(6) angstrom, c= 23.135(5) angstrom. The structure analysis of the BiS subsystem based on the superstructure model with space group B2mm leads to a distorted NaCl-like structure with short Bi-Bi bonding (3.120(8) angstrom).