The crystal structures of synthetic KSb5S8 and (Tl0.598, K0.402)Sb5S8 and their relation to parapierrotite (TlSb5S8)

The crystal structures of synthetic KSb5S8 and (Tl-0.598, K-0.402)Sb5S8 were determined from single crystal X-ray diffraction data: space group Pn, Z = 4, a = 8.1374(5) Angstrom, b = 19.5013(5) Angstrom, c = 9.0620(6) Angstrom, beta = 91.932(5)degrees (R = 4.11% for 5073 reflections), and a = 8.1148(9) Angstrom, b = 19.425(3) Angstrom, c = 9.0484(6) Angstrom, beta = 91.97(2)degrees (R = 4.53% for 4884 reflections). The structures were found to be isotypic with the parapierrotite (TlSb5S8) structure type which consists of Sb and S atoms occurring in slabs of the PbS archetype cut parallel to (211) which are interconnected by nine-fold coordinated Sb and M (= Tl, K) cations. Electron microprobe analyses proved the existence of a continuous series of solid solutions for the synthesized phases of intermediate composition for which the substitution of K for Tl was found to range between 15% and 89%. The refinement of the solid solution indicates that there is only minor effect of cation ordering, with a small site preference of K for M2.