In situ HT-XRD study on the formation of hexagonal ammonium tungsten bronze by partial reduction of ammonium paratungstate tetrahydrate

Hexagonal ammonium tungsten bronze, (NH4)(0.33-x)WO3-y, is a possible constituent of the intermediate "tungsten blue oxide" in non-sag (NS) tungsten production and a material of chromogenic and sensor interest. Its formation has been studied by in situ high-temperature powder X-ray diffraction (HT-XRD) accompanied by semiquantitative phase analysis through the partial thermal reduction of ammonium paratungstate tetrahydrate, (NH4)(10)[H2W12O2](.)4H(2)O, in flowing 10 % H-2/He. The effect of the heating program on the formation of the title compound has been discussed. Highly crystalline, monophasic hexagonal ammonium tungsten bronze prepared by partial reduction of ammonium paratungstate tetrahydrate has been characterised by high-precision powder XRD, X-ray photoelectron spectroscopy (XPS), chemical analysis and solid-state H-1 NMR spectroscopy (H-1-MASNMR). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)