Size effect in barium titanate powders synthesized by different hydrothermal methods

The size effect in barium titanate (BaTiO3) was investigated both experimentally and theoretically. Tetragonal BaTiO3 powders with average sizes from 80 to 420 nm were directly prepared by different hydrothermal methods. The tetragonality of the hydrothermal BaTiO3 decreased with decreasing particle size, which exhibited a dependence on the synthesis method. A phenomenological model for the size effect was proposed to interpret the experimental observations. The influence of the defects, mainly the lattice hydroxyl, on the size effect was investigated to understand the correlation between the size effect and synthesis condition. The permittivities of BaTiO3 powder at different particle sizes were calculated, which predicted a maximum permittivity of over 16 000 around the room-temperature critical size of similar to 70 nm. The prediction was in good accordance with the experimental data reported recently.