Structural role of large cations in sulfides with Cs+ and Tl+

Resumo

The results of a crystallographic analysis of the structures of CsFe₂S₃, Tl₂PbZrS₄, and Tl₂PbGeS₄ with a 1:1 cation–anion ratio are used to identify a joint F sublattice for Cs and S in the first compound and two separate F sublattices for cations and anions in the second compound (the PbS structural type). The substitution of the small Ge⁴⁺ (with its tetrahedral coordination by sulfur) for Zr⁴⁺ in the composition results in an increase in the unit cell volume, i.e., a decrease in the packing density for both cations and anions in the structure of the third compound. In the absence of regular F sublattices, there are “two-dimensional” orderings, typical of the PbS type, for the atomic positions in the projections of this structure.