Disorder of Cu+ in Cu3SbS3: structural investigations of the high- and low-temperature modification

Abstract

Abstract The crystal structure of α-Cu3SbS3 at 493 K and 403 K was determined 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) Å, b = 10.252(2) Å, c = 6.587(2) Å, and Z = 4 (T = 493 K). From single crystal data the distribution of the disordered copper atoms in the three-dimensional arrangement of [SbS3]3− units was determined. The atomic displacement parameters of the disordered copper atoms were refined using a Gram-Charlier non-harmonic development and a suggestion for a pathway for mobile copper atoms is derived. Copper atoms are distributed over five sites with trigonal planar or tetrahedral coordination and empty octahedra S6 are the bottlenecks for a three-dimensional movement. The crystal structure of γ-Cu3SbS3, which is stable below 264 K, was determined from X-ray powder data by the Rietveld method. The low-temperature modification crystallizes also in the orthorhombic system, space group P212121 (No. 19), a = 7.884(1) Å, b = 10.221(1) Å, c = 6.624(1) Å, and Z = 4 (T = 223 K). Whereas the arrangement of the thioantimonate(III) polyhedra keeps almost unchanged the copper atoms in the low-temperature modification γ-Cu3SbS3 are no longer disordered but are located in three different positions with triangular coordination by sulfur.