Position and oxidation state of tin in Sn-bearing tetrahedrites Cu12-xSnxSb4S13

We have explored the homogeneity range of Cu12-xSnxSb4S13 tetrahedrites, the peculiarities of their crystal structure, and the oxidation state of tin in them. Phase analysis and crystal structure refinement based on high-resolution powder X-ray diffraction have shown that tin-bearing tetrahedrites exist to the maximum of 0.75 divided by 0.8 tin atoms per formula, with the cubic unit cell parameter increasing from 10.331 to 10.391 angstrom. The analysis of atomic parameters have proved that tin substitutes for copper only on the Cu(1) site, which is characterized by a regular tetrahedral coordination. The substitution site is further confirmed by Sn-119 Mossbauer spectroscopy, showing the low quadrupole splitting, Delta = 0.14-0.16 mm s(-1), evidencing the highly-symmetric tetrahedral coordination of tin. Also, the +4 oxidation state of tin directly follows from the isomer shifts values, delta = 1.50-1.52 mm s(-1). (C) 2018 Elsevier B.V. All rights reserved.