On the sol–gel preparation of different tungstates and molybdates

Abstract

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 CaMo1-x W x O4 doped with Ce3+ ions, BaMo1-x W x O4 doped with Eu3+ ions and Gd2Mo3O12 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(MoO4)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.