On the sol-gel preparation of different tungstates and molybdates

The preparation and characterization of the M′-M″-O nitrate-tartrate (M′ = Ca, Ba, Gd and M′ = W, Mo) precursor gels synthesized by simple, inexpensive, and environmentally benign aqueous sol-gel method is reported. The obtained gels were studied by thermal (TG/DSC) analysis. TG/DSC measurements revealed the possible decomposition pathway of synthesized M′-M″-O nitrate-tartrate gels. For the synthesis of different metal tungstates and molybdates, the precursor gels were calcined at different temperatures (650, 800, and 900 °C). According to the X-ray diffraction (XRD) analysis data, the crystalline compounds CaMo_1-x W _x O₄ doped with Ce³⁺ ions, BaMo_1-x W _x O₄ doped with Eu³⁺ ions and Gd ₂Mo₃O₁₂ were obtained from nitrate-tartrate gels annealed at 650-900 °C temperatures. The XRD data confirmed that the fully crystalline single-phase powellite, scheelite, or Gd₂(MoO ₄)₃ structures were formed already at 650 °C. Therefore, the suggested sol-gel method based on the complexation of metal ions with tartaric acid is suitable for the preparation of mixed tungstates- molybdates at relatively low temperature in comparison with solid-state synthesis.