A new structure type in the hexagonal perovskite family; structure determination of the modulated misfit compound Sr9/8TiS3

Sr9/8TiS3, strontium titanium sulfide, a new phase in the hexagonal perovsk ite-like SrxTiS3 system, has been prepared and its structure solved from si ngle-crystal X-ray data within the (3 + 1)-dimensional [(3 + 1)D] formalism . Sr9/8TiS3 crystallizes with trigonal symmetry [R (3) over bar m(00 gamma) 0s superspace group], with the following lattice parameters: a(s) = 11.482 (3), c(s) = 2.9843 (8) Angstrom, q = 0.56247 (7)c* and V-s = 340.7 (3) Angs trom(3). The structure was considered as commensurate [R (3) over bar c thr ee-dimensional (3D) space group], but refined within the (3 + 1)D formalism to a residual factor R = 2.79% for 64 parameters and 1084 independent refl ections. Original crenel functions were used for the sulfur and strontium d escription. The structure is different from that of the hexagonal perovskit e-like oxide counterparts. The main difference is related to the presence o f a new type of polyhedron in the [MS3] transition metal chains, intermedia te between the octahedra classically found in such chains and the trigonal prismatic sites encountered in the oxides.