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Tetragonal BaTi03 thin films were prepared directly on Ti metal substrates in Ba(OH)2 solutions by a hydrothermal method at temperatures 400" to 800°C For 5 to 240 min. The film thickness estimated from weight gain of Ti plate was in the range from 0.5 to 2.5 pm, and it increased with increasing treatment temperature, treatment time, and Ba(OH)2 concentration. Rectangular crystals having (100) and (001) faces grew idiomorphically with approximate crystal size of 0.3 to 2.0 pm. The tetragonality of the BaTi03 films became apparent when the average crystal size exceeded about 1 pm. Lattice parameters of the films were a = 3.994 A, c = 4.035 A, and c/u = 1.010. The films formed above 600°C had preferred orientation showing stronger XRD peaks of hOO and 001 than the other peaks. [

Barium titanate (BaTiO3) particles with book‐like and spherical morphology were prepared by using a hydrothermal soft chemical process in the presence of a cationic surfactant. A layered titanate of H1.07Ti1.73O4 with a lepidocrocite‐like structure and plate‐like particle morphology was used as the precursor. The layered titanate was hydrothermally treated in a Ba(OH)2–(HTMA‐OH) (n‐hexadecyltrimethylammonium hydroxide) solution or a Ba(OH)2–(HTMA‐Br) (n‐hexadecyltrimethylammonium bromide) solution in a temperature range of 80°–250°C to prepare BaTiO3. The intercalation reaction of HTMA+ with the layered titanate promotes the structural transformation reaction from the layered titanates to BaTiO3, while it inhibits the structural transformation reaction to anatase under the hydrothermal conditions. The particle morphology of BaTiO3 prepared by this method dramatically changes with changing reaction conditions. HTMA+ plays an important role in changing particle morphology in the hydrothermal soft chemical process.