DISORDER OF CU- STRUCTURAL INVESTIGATIONS OF THE HIGH-TEMPERATURE ANDLOW-TEMPERATURE MODIFICATION( IN CU3SBS3 )

The crystal structure of alpha-Cu3SbS3 at 493 K and 403 K was determin ed from single crystal data. The high-temperature modification, which is stable above 394 K, crystallizes in the orthorhombic system, space group Pnma (No. 62), a = 7.808(1) Angstrom, b = 10.252(2) Angstrom, c = 6.587(2) Angstrom, and Z = 4 (T = 493 K). From single crystal, data the distribution of the disordered copper atoms in the three-dimension al arrangement of [SbS3](3-) units was determined. The atomic displace ment parameters of the disordered copper atoms were refined using a Gr am-Charlier non-harmonic development and a suggestion for a pathway fo r mobile copper atoms is derived. Copper atoms are distributed over fi ve sites with trigonal planar or tetrahedral coordination and empty oc tahedra S-6 are the bottlenecks for a three-dimensional movement. The crystal structure of gamma-Cu3SbS3, which is stable below 264 K, was d etermined from X-ray powder data by the Rietveld method. The low-tempe rature modification crystallizes also in the orthorhombic system, spac e group P2(1)2(1)2(1) (No. 19), a = 7.884(1) Angstrom, b = 10.221(1) A ngstrom, c = 6.624(1) Angstrom, and Z = 4 (T = 223 K). Whereas the arr angement of the thioantimonate(III) polyhedra keeps almost unchanged t he copper atoms in the low-temperature modification gamma-Cu3SbS3 are no longer disordered but are located in three different positions with triangular coordination by sulfur.