Kinetics and Mechanism of Aqueous Chemical Synthesis of BaTiO₃ Particles

A systematic kinetic investigation on the chemical synthesis of BaTiO 3 particles from aqueous solutions of BaCl 2 and TiCl 4 at T < 100 °C and at pH 14 has been performed. Initially, a viscous suspension of a Ti-rich gel phase is obtained at room temperature. Later, formation of BaTiO 3 is induced by heating above 70 °C and the gel phase is gradually converted to the crystalline perovskite. The isothermal formation kinetics of BaTiO 3 and the evolution of crystal size and particle size during the course of reaction are significantly influenced by temperature, concentration, and barium-to-titanium ratio of the solution. The early stages of reaction (yield < 1%) are dominated by primary nucleation, and slow formation of single nanocrystals of BaTiO 3 was observed by HRTEM. At a later stage, formation of polycrystalline particles occurs by secondary nucleation of BaTiO 3 on the surface of already existing crystals. During this stage, the reaction rate increases by 1 order of magnitude. When the yield exceeds 50%, nucleation becomes less important and the reaction is dominated by growth. Final particles have a diameter in the range 0.3−1.6 μm, depending on the processing parameters.