An X-ray and electron diffraction study of the intergrowth tungsten bronze Sb0.16WO3

The average structure of the orthorhombic antimony tungsten bronze, Sb0.16WO3, has been resolved by three-dimensional single-crystal X-ray- diffraction (space group Pmmm, a(av) = 7.4261(7), b(av) = 10.2004(15), c(av) = 3.8061(7) Angstrom, and Z = 5). The structure refinement based on 377 observed unique reflections with I > 2 sigma(I) (3493 totally measured reflections) converged to R = 0.064. The structure is of the intergrowth tungsten bronze type (ITB), consisting of slabs of hexagonal tungsten bronze structure (HTB) interchanged with slabs of perovskite-like WO3 structure (PTB) along [010]. The HTB slabs are one hexagonal tunnel thick and the PTB slabs are two WO6 octahedra thick. The Sb atoms are distributed over two positions inside the hexagonal tunnels. Electron diffraction observations revealed a superstructure with a(s) = 2a(av), b(s) = 2b(av), and c(s) = 4c(av), which may be attributed to an ordering of the Sb atoms. A possible structural model is proposed. (C) 1997 Academic Press.