Preparation of Barium Titanate Fine Particles by Hydrothermal Method and Their Characterization

Barium titanate fine particles with average particle sizes from 20 to 90 nm were prepared by a hydrothermal method using titanium tetrahydroxide gel and barium hydroxide. The particle size was inversely proportional to the Ba/Ti atomic ratio in the starting material, while it was independent of temperature in the narrow range from 70 to 150°C. For the explanation of these findings, we proposed the following mechanism for the formation of barium titanate fine particles, i.e., the nuclei of barium titanate form via the reaction of titanium tetrahydroxide gel with barium hydroxide and then grow. In these particles, there were many lattice defects in the form of hydroxyl groups and barium vacancies, and their concentration increased with decreasing particle size. We explained this result using the model that a particle can be divided into two parts: a defective surface layer with many defects and the bulk with fewer defects. The crystal structure of barium titanate particles was cubic with an expanded lattice (a-0.402nm) independent of particle size. This result indicated the possibility that the lattice defects influenced the crystal structure.