Kinetics and mechanism of aqueous chemical synthesis of BaTiO3 particles

A systematic kinetic investigation on the chemical synthesis of BaTiO3 particles from aqueous solutions of BaCl2 and TiCl4 at T < 100 degrees 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 BaTiO3 is induced by heating above 70 degrees C and the gel phase is gradually converted to the crystalline perovskite. The isothermal formation kinetics of BaTiO3 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 BaTiO3 was observed by HRTEM. At a later stage, formation of polycrystalline particles occurs by secondary nucleation of BaTiO3 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 mum, depending on the processing parameters.