Polymerized Complex Route to Barium Titanate Powders Using Barium‐Titanium Mixed‐Metal Citric Acid Complex

Abstract

Barium titanate (BaTiO3) powders were 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 13C‐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 13C‐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°C for 8 h or at 600°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°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°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.