Temperature dependence of the silver distribution in the crystal structure of natural pearceite, (Ag,Cu)(16)(As,Sb)(2)S-11

• Published in: Acta crystallographica. Section B, Structural science Structural science, 2006-04, Vol.62
• Main Authors: Bindi, L., Evain, Michel, Menchetti, S.
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Material chemistry
• ISSN: 0108-7681
• DOI: 10.1107/S010876810600108X

The crystal structure of the mineral pearceite, (Ag,Cu)16(As,Sb)2S11, has been solved and refined at 300, 120 and 15 K. At room temperature pearceite crystallizes with trigonal symmetry, space group P33m1; the refinement of the structure leads to a residual factor of R = 0.0464 for 1109 independent observed reflections and 92 variables. The crystal structure consists of sheets stacked along the c axis. The As atoms form isolated (As,Sb)S3 pyramids, which typically occur in sulfosalts, copper cations link two S atoms in a linear coordination, and the silver cations are found in a fully occupied position and in various sites corresponding to the most pronounced probability density function locations (modes) of diffusion-like paths. These positions correspond to low-coordination (2, 3 and 4) sites, in agreement with the preference of silver for such environments. d10 silver-ion distribution has been determined by means of a combination of a Gram–Charlier description of the atomic displacement factors and a split-atom model.