Crystal structure refinement of a wallisite- hatchite solid solution
Boiocchi, Massimo; Callegari, Athos
published: Sep 15, 2003
X-ray single-crystal diffraction data of a wallisite-hatchite solid solution (from Binnatal, Switzerland) have been collected using a Bruker-Axs three-circle diffractometer equipped with the Smart-Apex CCD detector. The chemical formula of the studied crystal is: PbTl(Cu0.64Ag0.36)As2S5. It is triclinic, with a = 9.071(1), b = 7.787(1), c = 8.039(1), α = 65.83(1), β = 65.05(1), γ = 74.22(1), space group P 1¯, Z = 2. The original determinations of the crystal structure proposed by Marumo & Nowacki (1967) for hatchite and by Takéuchi et al. (1968) for wallisite are substantially confirmed. Our structure refinement [which converges to Robs = 0.038 for 3054 observed reflections with I/σ(I) ≥ 3] allows a better description of the structural features and of the crystal-chemical behaviour along the hatchite-wallisite binary join. The mean atomic number refined at the tetrahedral (T) site agrees with the estimated chemical formula, whereas the partitioning of Pb and Tl between the two independent M site is proposed combining geometrical and bond valence considerations.