HYDROTHERMAL SYNTHESIS OF TETRAGONAL BARIUM-TITANATE

Hydrothermal synthesis of BaTiO3 at 240-degrees-C in the presence of chloride ions leads to the formation of the tetragonal polymorph upon cooling through the Curie temperature. In the absence rf Cl-, the metastable cubic structure is formed. Though the exact role of Cl- is not clear, it appears that it leads to formation of larger (approximately 1-mu-m) crystals as compared to smaller crystals (approximately 0.2-mu-m) in its absence. Combination of diffraction and calorimetry provides unambiguous support for the presence of the tetragonal form.