Synthesis of fine-particle titanates by the pyrolysis of oxalate precursors

Abstract

Fine-particle MTiO₃, where M=Ca, Sr, Ba or Pb, were prepared by the pyrolysis of MTiO(C₂O₄)₂·4H₂O in the presence of a redox mixture containing NH₄NO₃ and oxalic acid dihydrazide at 350 °C. The redox mixture, having a low ignition temperature, not only pyrolyses the oxalate precursor but also produces large quantities of gases, which results in a fine, foamy oxide product. The exothermicity of the redox reaction provides the heat required for the decomposition of the oxalate, and the gases evolved create the foamy nature of the product and help to dissipate the heat, which inhibits the sintering of MTiO₃. Metal titanate powders obtained by the pyrolysis of the oxalates are of submicrometre size and have a high surface area (18–42 m²g⁻¹). The sintered BaTiO₃ and PbTiO₃ showed spontaneous polarization of 12 and 26 µC cm⁻², respectively, for a field strength of 120 kV cm⁻¹.