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

水热合成是一种以高压高温水溶液为反应性溶剂或试剂的合成方法，已被应用于陶瓷：无机化合物和/或其复合材料。特别是在本研究中，通过钛金属衬底与溶剂的模拟反应，在较低的温度(120~200ﾟ℃)、饱和蒸气压为0.2~2 Mpa下反应1h，可以在钛金属衬底上制备出钙钛矿型BaTiO_3等功能复合氧化物薄膜，该方法还可以制备PbTiO_3、SrTiO_3和CaTiO_3薄膜。同样，在Nb衬底上合成了BaNbO_3、LiNbO_3和Ba5Nb_4O_(15)，在Ta衬底上合成了LiTaO_3。在40 0~70 0ﾟC的水热条件下，在钛衬底上制备了四方相BaTiO_3多晶薄膜。成功地在钛酸锶衬底上外延生长了BaTiO_3。产物经X射线衍射、扫描电子显微镜和/或拉曼光谱确证。如果能在TiAl衬底上制备合适的抗氧化涂层，则可以在TiAl上制备碱土钛酸盐薄膜，有望成为未来的高温材料之一。在900ﾟC空气中循环加热，发现CaTiO_3薄膜对TiAl的氧化有一定的延缓作用。

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.