The formation mechanism of barium titanate thin film under hydrothermal conditions

Barium titanate thin films were produced under the hydrothermal conditions, and their formation mechanism was investigated. The phase structure and surface morphology of the resultant films were directly dependent on the reaction conditions. The films that have a reaction time shorter than 8 h below the processing temperature of 150 °C in the 0.8 N Ba(OH)₂ solution were composed of compounds with the component ratio m(Ba)/ m(Ti) < 1, and a flower-like surface morphology. With extended reaction time under the higher temperature, the films showed a multiphase structure and a mosaic or island-like surface morphology. In the case of 1.0 N, 1.5 N Ba(OH)₂ solution, well-crystallized, monoperovskite BaTiO₃ thin films having uniform, mirror-like, and visible-defectless surfaces were produced at a processing temperature of 180 °C after 24 h. The experimental results were explained by hypothesizing that the formation mechanism consists of a “dissolutions-crystallization process”.