Hydrothermal synthesis and formation mechanism of tetragonal barium titanate in a highly concentrated alkaline solution

Tetragonal cube-shaped barium titanate (BaTiO3) was produced by the hydrothermal treatment of a peroxo-hydroxide precursor, a single-source amorphous barium titanate precursor, in a highly concentrated sodium hydroxide solution. Phase pure barium titanate with cube-shaped morphology and particle-sizes in the 0.2–0.5 µm range were formed at temperatures above 80 °C. Also, the cube-shaped morphology of the BaTiO3 product was preceded by spherical- and plate-like morphologies with, respectively, a Ti-excess and Ba-excess. Coinciding with these morphological observations, changes in the reaction product were also observed. The formation of crystalline BaTiO3 proceeded alongside secondary BaTi2O5 and Ba2TiO4 phases. These secondary phases disappeared as the reaction time was increased leaving only BaTiO3 as the sole reaction product. Kinetic analysis of the formation of hydrothermal BaTiO3 crystallization by the Johnson-Mehl-Avrami method showed that BaTiO3 crystallization is a homogeneous dissolution-precipitation reaction. The mechanism is governed by nucleation and growth in the beginning of the reaction and dissolution-precipitation dominating throughout the hydrothermal reaction process.