X-Ray and Electron Diffraction Study of the Tetragonal Sodium Tungsten Bronze, Na0.10WO3, with Distorted Perovskite Structure

Abstract

The crystal structure of the tetragonal sodium tungsten bronze, Na0.10WO3, was investigated by single-crystal X-ray and electron diffraction methods. The average structure has space groupP4/nmmand cell constantsaav=5.2492(5) Å,cav=3.8953(4) Å, andZ=2. The superstructure has space group very probablyP4 and cell constantsas=7.423(3) Å,cs=7.791(1) Å, andZ=8. Full-matrix least-squares refinements resulted in a conventionalRvalue of 0.041 [86 observed unique reflections,I>2σ(I)] for the average structure and anRvalue of 0.086 [537 observed unique reflections,I>2σ(I)] for the superstructure. The general features of the average structure, which is of distorted perovskite type, are the same as those reported earlier (A. Magnéli, 1951.Acta Chem Scand. 5, 670). The two axial bonds of the WO6octahedron are not equal (1.95 Å ) as observed in the previous work but have significantly different lengths [1.63(6) and 2.27(6) Å]. The superstructure, reported for the first time, results from the average structure by the combined effects of tilting of the WO6octahedra about c leading to a doubling of this axis (cs=2cav) and of shape deformation of these octahedra in theabplane leading to a supercell in this plane withas=2aav.