Structural controlling in nano-scale and high-functionalization for multi-component ferroelectric oxide films by chemical vapor deposition

点击翻译按钮获取中文摘要

There are lots of ferroelectric, piezoelectric, pyroelectric and optical materials in multi-component oxides, for example BaTiO_3, PbTiO_3, Bi_4Ti_3O_<12>, and LiNbO_3. It is necessary to prepare films of these materials and to achieve high-functionalization. We treid to prepare films of ferroelectric bismuth titanate (Bi_4Ti_3O_<12>) which belongs to multi-component oxide by chemical vapor deposition (CVD) and clarify the relationship of CVD condition of nano-scale structural controlling and ferroelectricity of the film.We have successfully controlled the composition of BIT films by using tri-ortho-tolyl-bismuth [Bi (o-Tol)_3] and di-isopropoxy-bis- (dipivaloyl metanato) -titanium [Ti (i-C_3H_7O)_2 (DPM)_2] as Bi and Ti sources. The films were stoichiometric and single phase. The film with excess Ti contains Bi_2Ti_2O_7 phase and the film with excess Bi contains Bi_<12>TiO_<20> as second phases. Crystal orientation and crystallite size were controlled in nano-scale. We found that the mechanisms of epitaxial and preferred growth depend on kinds of substrates and substrate temperatures. Grains size of the BIT films observed by electron microscope were nano-meter size. Uniformity of crystal orientation of these nano-scale grains improved with increasing substrate temperature.The value of the residual polarization increased and the coercive field decreased with increasing film thickness. When the thickness of the film were above 5mum, these value of BIT film were almost the same as the values of single crystals.