Solid state synthesis of barium titanate in air and in supercritical water: Properties of powder and ceramics

BaTiO3 powders synthesized by two different methods based on the solid-state mechanism of formation were studied as raw materials for ferroelectric ceramics production. Fine-crystalline BaTiO3 obtained by reaction between BaO and TiO2 in supercritical water at 400 degrees C and 26 MPa had superior properties to the powder obtained by conventional high-temperature synthesis in air at 1100-1300 degrees C. Quasi-reversible interaction of water molecules with solid oxides in supercritical region had beneficial effect on morphology and phase purity of BaTiO3. Ceramics manufactured from the powders synthesized in supercritical water possessed uniform microstructure and narrow grain size distribution. This ceramic material performed ferroelectric phase transition at temperature of about 130 degrees C and possessed dielectric permittivity up to 8650 and the loss tangent lower then 0.02 at 1 kHz. BaTiO3 powder synthesized in supercritical conditions appeared to be an affordable and high quality raw material for ferroelectric ceramics compared to the powder obtained by high-temperature solid-state method.