A new molecular precursor route for the synthesis of Bi-Y, Y-Nb and Bi-doped Y-Nb oxides at moderate temperatures

Yttrium-based multimetallic oxides containing bismuth and/or niobium were prepared by a method starting from pre-isolated stable water-soluble precursors which are complexes with the ethylenediaminetetraacetate ligand (edta). The cubic Bi_1−xY_xO_1.5 (x=0.22, 0.25 and 0.3) and Y₃NbO₇ oxides were obtained in a pure form in a range of moderate temperatures (600-650 °C). This preparation method also allowed to stabilize at room temperature, without quenching, the tetragonal YNbO₄ oxide in a distorted form (T′-phase) by calcining the precursor at 800 °C. When heated up to 1000 °C, this metastable T′-phase transforms into the metastable “high-temperature” T oxide, which converts on cooling down to room temperature into the thermodynamically stable monoclinic M oxide. Doping the YNbO₄ oxide with Bi³⁺ cations (0.5% and 1% Bi with respect to total Bi+Y amount) led at 800 °C to a mixture of the T′-phase and the thermodynamically stable monoclinic one. At 900 °C, the almost pure monoclinic structure was obtained.