FORMATION OF BATIO3 FROM CITRATE PRECURSOR

On thermal decomposition barium bis(citrato)oxotitanate (IV) citrate heptahydrate produces stoichiometric BaTiO3 fine powders at about 650-degrees-C. Thermal decomposition of the precursor proceeds through three major stages, viz. (i) dehydration, (ii) decomposition of the citrate to form an oxycarbonate intermediate Ba2Ti2O5CO3, and (iii) decomposition of the intermediate carbonate to form BaTiO3. Spectroscopic and thermoanalytical techniques are presently employed to characterize the precursor and the intermediates isolated at various stages. As-prepared BaTiO3 is a mixture of cubic and tetragonal phases. The primary particle size of the powder is on the order of 100 nm, as revealed by the TEM technique. Calcining the powders above 800-degrees-C results in the formation of complete tetragonal phase with improved crystallinity. The resultant powders are sinter active to give dense monophasic ceramic compacts having densities in the range 95-99% of the theoretical value. Depending on the processing conditions, the dielectric constant (epsilon(r)) varies from 1600 to 3000 at 1 kHz, while the dielectric loss, tan delta, ranges from 0.003 to 0.009 at 300 K. (C) 1994 Academic Press, Inc.