Cubic to Tetragonal Phase Transformation of Ultrafine BaTiO₃ Crystallites at Room Temperature

The critical crystallite size for the cubic (c-) to tetragonal (t-) phase transformation of ultrafine BaTiO 3 crystallites was examined. Crystallites were prepared by calcination of barium titanyl oxalate tetrahydrate (BTOT) at various temperatures as to obtain crystallites with different sizes. The c- BaTiO 3 crystallite which is thermodynamically considered as a high-temperature form can exist at room temperature if the crystallite is smaller than certain size. The critical size for the c→t phase transformation is ∼30 nm. The size may become larger if the crystallite suffers higher lattice strain which can be induced by different powder preparation methods.