Synthesis of Crystal-Axis-Oriented BaTiO₃ and Anatase Platelike Particles by a Hydrothermal Soft Chemical Process

BaTiO 3 and anatase with platelike particle morphology were prepared by using a hydrothermal soft chemical process. A layered titanate of K 0.8 Ti 1.73 Li 0.27 O 4 with a lepidocrocite-like layered structure, which has a platelike particle morphology, was used as a precursor. In the first step, the layered titanate was treated with an acid solution to obtain an H + -form layered titanate H 1.07 Ti 1.73 O 4 · n H 2 O with a lepidocrocite-like layered structure. In the second step, the H + -form layered titanate was treated in a Ba(OH) 2 solution or distilled water under mild hydrothermal conditions to transform the layered titanate to BaTiO 3 or anatase. The transformation reactions were investigated by XRD and SEM analyses. There are two simultaneous mechanisms in the formation of BaTiO 3 under the hydrothermal conditions. One is an in situ topotactic transformation reaction in the crystal bulk of the layered titanate, and another is a dissolution−deposition reaction on the surface of the particles. In the formation of BaTiO 3, the in situ topotactic transformation reaction is predominant in the solution of low Ba(OH) 2 concentration, while, in the formation of anatase, most of the reaction progressed by the in situ topotactic transformation mechanism. The platelike particles of BaTiO 3 and anatase, which were prepared by this method, showed a high degree of crystal-axis orientation.