THE CRYSTAL-STRUCTURE OF SKINNERITE, P2(1) C-CU3SBS3, FROM POWDER DATA/

The crystal structure of the room-temperature polymorph of skinnerite, Cu3SbS3, was determined by the Rietveld method from Guinier diffracto meter X-ray powder data, The space group is P2(1)/c; the cell paramete rs are a 7.814(1), b 10.242(1), c 13.273(1) Angstrom, beta 90.29(1)deg rees, with Z = 8. The sulfur framework can be described as a (deformed ) (11(2) over bar 2)(hop) twinned hcp array. Sb has trigonal pyramidal coordination in the bases of trigonal coordination prisms created by the unit-cell twinning of the S array. The Sb-S bond is between 2.44 a nd 2.47 Angstrom in length. Most Cu sites have a triangular coordinati on, with <Cu-S> distances in the range 2.26-2.31 Angstrom. Cu4 is spli t into two irregularly tetrahedral, [3 + 1] coordinations, with <Cu-S> in the range 2.40-2.46 Angstrom. Cu3 and Cu4 are in triangular faces common to two tetrahedral voids of the S array, and the remaining Cu a toms are in such faces common to tetrahedral and octahedral voids. P2( 1)/c-skinnerite is a low-temperature polymorph of the ionic conductor Cu3SbS3. Differences in the distribution of Cu between P2(1)/c-skinner ite and P2(1)2(1)2(1)-wittichenite are caused by different sizes of Sb and Bi coordination polyhedra.