Aqueous Synthesis of Barium Titanate and Its Dielectris, Properties

Barium titanate was successfully prepaxed threugh an aqueous reaction between Ba(OH)2and TiCl4. The dried materials had a cubic perovskite-type structure loosely crystallized. The heat-treatment promoted the crystallization and decrease in its lattice constant. The cubic phase was changed into the tetragonal one by firing at 1200 C. The firing at higher temperature enlarged the tetragonality and c/a became 1.0057 by firing at 1400 C. Although chemical analyses showed that it was almost stoichiometric, compound except that contained O.14wt%Na, it showed the existence of lattice defect because the density observed was considerably smaller than that of the calculated one. In comparison with barium titanate prepared by solid-state reaction between BaCO3 and TiO2, the barium titanate aqueously prepared had a low relative permittivity, a low Curie temperature, and broad peak width of dielectric anomaly at the transition point from ferroelectric to paraelectric phase. These characteristics were interpreted in terms of lattice defect, concentration of which was estimated from the difference between the observed density and the calculated one. The lattice defect seemed not to be due to a special ion deficiency, but to vacancies of all components of BaTiO3 with a vacancy ratio corresponding to the chemical formula.