RIETVELD REFINEMENT OF POWDER X-RAY DIFFRACTION OF NANOCRYSTALLINE NOBLE METALS - TUNGSTEN TRIOXIDE

Tungsten trioxide powders were prepared from peroxo-tungstic acid (PTA) precursor obtained by sol-gel route, in aqueous medium. Two WO3 samples were doped with noble metals, by "loading" them with silver and metallic palladium. The unit cell parameters of the WO3 monoclinic phase, the effective crystallite mean size, D-eff (nm), and the mean root mean square (rms) of the microstrains, <epsilon(2)>(1/2)(hkl),were calculated by Rietveld refinement analysis. The distorsion of the WO3 crystal structure has been used by the ISODISPLACE software tool to transform the P2_1/n structure of WO3 on to the distortion-mode basis to visualize and quantify the displace modes. The atomic coordinate type has been used to compute three-dimensional structure model as the Radial Distribution Functions g(r) for a 3000-atom model of WO3-Ag and WO3-Pd systems, which reflects the space correlations between W-O and W-W atoms.