Composite crystal Sr8/7TiSy with y = 2.84–2.97

Abstract Sr 8/7 TiS y ( y =2.84–2.97) has been prepared by controlling the partial pressure of sulfur. The XRD and the ED patterns could not be indexed because of incommensurate structures; they were, therefore, indexed by four-dimensional formalism with simple lattice parameters of A , C Ti and C Sr in a hexagonal setting. However, a commensurate structure was obtained at y =2.84 in Sr 8/7 TiS y , the XRD and ED patterns of which were indexed by three- and four-dimensional formalisms. The sulfides, including incommensurate and commensurate structures, could be regarded as a single phase with a homogeneity range of sulfur of y =2.84–2.97, when the four-dimensional formalism was used. On the other hand, from the viewpoint of three-dimensional formalism, the structure contains two penetrating hexagonal subcells. The lattice parameter “ a ” in hexagonal setting is common to both subcells, while c is given by c = pC Ti = qC Sr , where p and q are integers, and C Ti and C Sr are the periodicities in c -direction of the two subcells, respectively. Hence, there is an infinite number of the structures in the composition range of y =2.84–2.97 in Sr 8/7 TiS y .