Synthesis of Barium Titanate by Hydrothermal Method and Its Formation Mechanisms

The formation of nano-sized barium titanate powders by hydrothermal reaction between barium hydroxide octahydrate and hydrous titania was studied at various temperatures, times and reactant concentrations without mineralizer. FTIR, TGA, SEM, XRF, BET and XRD were used to investigate the effects of temperature, time and concentration on reactivity, particle size, morphology and secondary phase of BaTiO3 powder prepared hydrothermally. The main impurities were BaCO3, TiO2, surface H2O and lattice OH– radical at low conversion while secondary phase such as the lattice hydroxyl radical and trace BaCO3 remained at high conversion. As the temperature and time increased in low concentration reaction below 0.5 M, the maximum conversion could not exceed 98% but the conversion increased with increasing concentration, reaching over 99% above 1.5 M. In addition, concentration of more than 1.5 M was favorable to smaller particle size, better sphericity and Ba/Ti ratio ≒ 1. Kinetic analysis by the Johnson–Mehl–Avrami plot shows hydrothermal reaction progresses through solidification path. Initially, dissolution-precipitation mechanism takes place to form the nuclei of BaTiO3 through fast dissolution of TiO2·xH2O and reaction with Ba2+ ions and then the BaTiO3 crystal begins to grow.