The Order–Disorder Character of Owyheeite

Abstract

Owyheeite, Ag1.5Pb4.43Sb6.07S14, monoclinic and pseudo-orthorhombic, is invariably intimately twinned, and its structure displays an alternation of two types of unit order-disorder (OD) layers, with layer symmetries P (2/ n ) 2(1)/ m 2(1)/ m for the thicker OD layer, and P (1) 1 2(1)/ m for the three-times thinner OD layer. These layers occur in two orientations, indexed as (021) and (021) of the owyheeite lattice. Ambiguity in the orientation of the thinner OD layer after the thicker one leads to intimate twinning (stacking disorder). Pseudohexagonality of the lattice ( b × √3/2 ≈ c ) with two alternative sets of OD layers further complicates the twinning situation, which also can be described using a rod representation of the structure.