Polymerized complex route to barium titanate powders using barium-titanium mixed-metal citric acid complex

Barium titanate (BaTiO3) powders mere prepared by a polymerized complex method based on the Pechini-type reaction route, wherein a mixed solution of citric acid (CA), ethylene glycol (EG), and barium and titanium ions, with a molar ratio of CA:EG:Ba:Ti = 10:40:1:1, was polymerized to form a transparent resin, which was used as a precursor for BaTiO3. Characterization of the initial precursor solution of EG, CA, and barium and titanium ions by Raman scattering and C-13-NMR spectroscopy indicated that barium and titanium ions were simultaneously stabilized with CA to form a barium-titanium mixed-metal CA. complex with a stoichiometry similar to Ba:Ti:CA = 1:1:3. Raman and C-13-NMR spectra of the liquid mixture at various reaction stages indicated that the fundamental coordination structure of the mixed-metal complex remained almost unchanged throughout the polymerization process. X-ray diffractometry (XRD) measurements indicated formation of pseudo-cubic BaTiO3 free from BaCO3 and TiO2 when the barium-titanium polymeric precursor was heat-treated in air at 500 degrees C for 8 h or at 600 degrees C for 2 h. However, the Raman spectra of the same powders indicated the formation of tetragonal (rather than cubic) BaTiO3, with traces of high-temperature hexagonal BaTiO3 stabilized at room temperature, XRD of a pyrolyzed product at 500 degrees C for 2 h revealed a simple mixture of BaTiO3 and an intermediate phase, Ba2Ti2O5 . CO3. A solid-state reaction between BaCO3 and TiO2 was concluded as not being responsible for the BaTiO3 formation; rather, BaTiO3 formed directly by thermal decomposition of the intermediate Ba2Ti2O5 . CO3 phase at temperatures >500 degrees C. In addition, by Raman scattering measurements, the intermediate Ba2Ti2O5 . CO3 phase was found to be unstable in ambient air, yielding BaCO3 as one of the decomposed products.