Acta Cryst. (2006). B62, 768-774 [ doi:10.1107/S0108768106022798 ]
Abstract: The crystal structure of a Se-rich antimonpearceite has been solved and refined by means of X-ray diffraction data collected at temperatures above (room temperature) and below (120 K) an ionic conductivity-induced phase transition. Both structure arrangements consist of the stacking of [(Ag,Cu)6(Sb,As)2(S,Se)7]2- A (A') and [Ag9Cu(S,Se)2Se2]2+ B (B') module layers in which Sb forms isolated SbS3 pyramids typically occurring in sulfosalts; copper links two S atoms in a linear coordination, and silver occupies sites with coordination ranging from quasi-linear to almost tetrahedral. In the ionic-conducting form, at room temperature, the silver d10 ions are found in the B (B') module layer along two-dimensional diffusion paths and their electron densities described by means of a combination of a Gram-Charlier development of the atomic displacement factors and a split-atom model. The structure resembles that of pearceite, except for the presence of both specific (Se) and mixed (S, Se) sites. In the low-temperature `ordered' phase at 120 K the silver d10 ions of the B (B') module layer are located in well defined sites with mixed S-Se coordination ranging from quasi-linear to almost tetrahedral. The structure is then similar to that of 222-pearceite but with major differences, specifically its cell metric, symmetry and local arrangement in the B (B') module layer.
Keywords: Se-rich antimonpearceite; X-ray crystal-structure determination; twin; phase transition; disorder.
 |   Structure factor file (CIF format) (59.5 kbytes) |
| Structure factor file (CIF format) (1297.8 kbytes) |
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