Crystallographic Properties of Hydrothermal Barium Titanate Crystallites

The crystallographic properties and defects of hydrothermally grown barium titanate crystallites are reported. When a precursor with a Ba:Ti molar ratio of 1.0 was used, cubic barium titanate crystallites were formed. However, when the precursor Ba:Ti molar ratio was 3.0, the product was tetragonal. The defect concentration (including OH defects and barium vacancies) was higher in cubic crystallites than in tetragonal crystallites. Because of the defects in the crystallites, the displacement of Ba²⁺ cations and the deformation of the Ti-O₆ octahedrons was suppressed; thus, no phase transition from cubic to tetragonal occurred at the Curie point. When the defects were eliminated by thermal treatment, the normal crystallographic properties were obtained. A high reaction temperature and a high Ba:Ti molar ratio in the precursor were beneficial to limiting defect dormation in the crystallites; thus, tetragonal crystallites were obtained.