Nb-Ta, Nb-Ta-V, and Nb-Ta-Bi Oxides Prepared from Molecular Precursors Based on EDTA

Multimetallic oxides of general formula (TaxNb1-x)2O5, TaxNb1-xVO5, and BiTaxNb1-xO4 (0 < x < 1) are synthesized by a molecular precursors method from pre-isolated water-soluble EDTA complexes. These materials are obtained by thermal treatment in air of a homogeneous mixture of precursors of the metals to be incorporated in the final oxide. The obtention of a solid solution over the entire range of composition is evidenced, for the three systems studied, by Raman spectroscopy but also by DTA/DSC analyses and powder X-ray diffraction. The incorporation of small amounts of tantalum in the Nb-V-O and NbBi-O systems is shown to stabilize phases difficult to obtain in a pure form, like the NbVO5 and ?-BiNbO4 phases. Moreover, the pore size distribution measurements and SEM pictures of the ternary and quaternary oxides reveal the (TaxNb1-x)2O5 and BiTaxNb1-xO4 phases display a disordered porous character. The TaxNb1-xVO5 oxides present a high crystallinity.