BaTiO_3 Particle Formation Mechanism under Hydrothermal Conditions

摘要

Solid-state kinetic analysis by the Johnson-Mehl-Avrami plot was introduced to understand the reaction mechanism of fine BaTiO_3 powders prepared under hydrothermal conditions. In the experiment reactants were dissolved and consumed to spherical particles of 50 nm from aggregation of several nanometer-sized particles. The particulate formation of BaTiO_3 underwent 1st-order hydrolysis-condensation reaction with phase-boundary transition in the early stage of the reaction regardless of the initial concentration of the feedstock. However, as the concentration of nutrients reduced, dissolution followed by precipitation became dominant, and a diffusion-controlled reaction proceeded. When the concentration of nutrients reduced to an extent that was not high enough to sustain supersaturation, the reaction was controlled by solidification for encapsulation of aggregated particles, inside of which the diffusion-controlled reaction slowly proceeded.