Preparation and Evolution of Functional Double Oxide Thin Films by Hydrothermal Electrochemical Methods

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Hydrothermal synthesis, where high pressure and high temperature aqueous solutions are reactive solvents or reagents, has been applied to ceramics: inorganic compounds and/or their composites. In particular,in the present study, functional double oxides such perovskite-type oxides as BaTiO_3 could be prepared as thin films on Ti metal substrate through in sim reactions between the substrate and the solvent at relatively low temperatures of 120-200ﾟC under saturation vapor pressure of 0.2-2 MPa for 1 h. PbTiO_3,SrTiO_3 and CaTiO_3 also could be prepared as films by this method. Similarly, BaNbO_3,LiNbO_3 and Ba_5Nb_4O_<15> on Nb substrate, and LiTaO_3 on ta substrate have been synthesized. Polycrystalline tetragonal BaTiO_3 films were prepared on Ti substrate at 400-700ﾟC under hydrothermal conditions. Epitaxial growth of BaTiO_3 on SrTiO_3 substrate has been succeeded. These products were confirmed through X-ray diffraction, scanning electron microscope and/or Raman spectroscopy. Alkaline earth titanate films could be prepared on TiAl that is expected as one of future high temperature materials if appropriate anti-oxidative coating could be prepared on the TiAl substrate. It was observed that CaTiO_3 films could retard the oxidation of TiAl by cyclic heating at 900ﾟC in air.