CRYSTAL-STRUCTURE OF A HEXAGONAL TIN TUNGSTEN BRONZE PREPARED BY A MILD REACTION

The tin tungsten bronze SnxWO3 (x= 0.26-0.33) has been prepared by a n ew, mild reaction between tin powder and tungstic acid in water at 95- 100 degrees C and crystallized at higher temperature. The samples were characterized by single-crystal and powder X-ray diffraction as well as transmission electron microscopy (TEM). The black phase yielded cry stals with hexagonal prismatic shape, the diffraction pattern of which could be indexed by a hexagonal unit cell with a = 7.429 (1), b= 7.42 9 (2) and c= 3.7868 (8) Angstrom alpha=beta=90, gamma=120 degrees. The space group was later assigned to be P6/mmm, eliminating seven other possible hexagonal space groups by refinement techniques. Eight possib le trigonal space groups could be excluded by examining I(($) over bar hkl) and I(h $($) over bar$$ kl) reflections on Weissenberg photograp hs and on the measured data set, which are equal in the hexagonal case . The position of tungsten is 0, 1/2, 0; Sn is disordered at x=0.940(2 ), y=0.950 (2), z=0. The oxygen positions are O-1:1/2, 0, 1/2 and O-2: 0.208(1), 0.419(3), 0.0. The TEM examination confirmed this structure .