Hydrothermal precipitation and characterization of nanocrystalline BaTiO3 particles

Crystalline BaTiO3 powders were precipitated by reacting fine TiO2 particles with a strongly alkaline solution of Ba(OH)2 under hydrothermal conditions at 80 degreesC to 240 degreesC. The characteristics of the powders were investigated by X-ray diffraction, transmission electron microscopy, thermal analysis and atomic emission spectroscopy. For a fixed reaction time of 24 hours, the average particle size of BaTiO3 increased from similar to 50 nm at 90 degreesC to similar to 100 nm at 240 degreesC. At synthesis temperatures below similar to 150 degreesC, the BaTiO3 particles had a narrow size distribution and were predominantly cubic in structure. Higher synthesis temperatures produced a mixture of the cubic and tetragonal phases in which the concentration of the tetragonal phase increased with increasing temperature. A bimodal distribution of sizes developed for long reaction times (96 h) at the highest synthesis temperature (240 degreesC). Thermal analysis revealed little weight loss on heating the powders to temperatures up to 700 degreesC. The influence of particle size and processing-related hydroxyl defects on the crystal structure of the BaTiO3 powder is discussed. (C) 2001 Kluwer Academic Publishers.