The influence of concentration on the formation of BaTiO3 by direct reaction of TiCl4 with Ba(OH)2 in aqueous solution

The formation of fine BaTiO3 particles by reaction between liquid TiCl4 and Ba(OH)2 in aqueous solution at 85 °C and pH⩾13 has been studied for 0.062⩽[Ba2+]⩽0.51 mol l−1. The concentration of Ba2+ ions has a strong influence on reaction kinetics, particle size and crystallite size. When [Ba2+]>≈0.12 mol l−1, the precipitate consists of nanosized (≈30 nm) to submicron (100–300 nm) particles of crystalline BaTiO3. At lower concentrations, the final product is a mixture of crystalline BaTiO3 and a Ti-rich amorphous phase even for very long reaction times. A two-steps precipitation mechanism is proposed. Initially, a Ti-rich amorphous precipitate is rapidly produced. Reaction between the amorphous phase and the Ba2+ ions left in solution then leads to crystallisation of BaTiO3. In addition to nucleation and growth of nanocrystals, the final size and morphology of BaTiO3 particles obtained at low concentration can be determined by aggregation of nanocrystals and heterogeneous nucleation on existing crystal surfaces.