Thermal degradation of polyoxotungstates - An effective method for the preparation of tungsten bronzes

The thermal degradation of ammonium salts of five polyoxotungstates, [(As12 Ce16III)-Ce-III(H2O)(36)W148O524](76-) I, [(As5Ce4III)-Ce-III (H2O)(4)W39O1 43](25-) II, [As-3(III)((UO2)-O-VI)(3)(H2O)(6)W30O105](15-) III, [(W5O18)(2 )Ce-III](9-) IV, and [(W5O18)(2)Th-IV](8-) V, in hydrogen up to 500 degrees C and in argon or nitrogen up to 950 degrees C was studied by means of the rmal analysis (TG, DSC), X-ray diffraction methods, chemical analysis, and susceptibility measurements. X-ray analyses of the resulting deeply colored , arsenic-free powders, revealed the formation of cubic tungsten bronzes of cerium(III) CexWO3, x = 0.066-0.162 with lattice parameters ranging from a = 3,820(3) to 3.836(3) Angstrom, of thorium(IV) ThxWO3, x similar to 0.1 w ith x = 3.836(3) Angstrom, and of uranium(IV) UxWO3, x similar to 0.1 with a = 3.797(1) Angstrom as the main product in all experiments. These cubic b ronzes were obtained in a one-step solid-state process at significantly low er temperatures than those reported previously by using classical methods o f synthesis, (C) 2000 Academic Press.