AN X-RAY AND ELECTRON-DIFFRACTION STUDY OF THE INTERGROWTH TUNGSTEN BRONZE SB0.16WO3

The average structure of the orthorhombic antimony tungsten bronze, Sb 0.16WO3, 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 base d 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 hexago nal tungsten bronze structure (HTB) interchanged with slabs of perovsk ite-like WO3 structure (PTB) along [010]. The HTB slabs are one hexago nal 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 propose d. (C) 1997 Academic Press.