Abstract

The study of BaTiO₃ crystallization from X-ray amorphous (Ba,Ti) polymeric organic powders has been carried out by comparing samples previously heat-treated in air at 250 and 400 °C. From thermal analysis, X-ray diffraction, infrared and Raman spectroscopies, and ¹³C NMR spectroscopy, it has been found that the BaTiO₃ formation strongly depends upon the initial structure of the used precursor. It is concluded that an intermediate oxycarbonate phase was formed prior to the formation of BaTiO₃ above 550 °C when the precursor used was a (Ba,Ti)-mixed metal organic complex heat-treated at 250 °C, and a nanocrystalline BaCO₃ intermediate when the metal organic complex had been initially heat-treated at 400 °C. Although not well crystallized, thermoanalytical measurements, the unique XRD pattern, and new IR and Raman structural features revealed that such a metastable intermediate oxycarbonate phase has a stoichiometry close to Ba₂Ti₂O₅·CO₃, which is characterized by having CO₃²⁻ groups different to those of pure BaCO₃ located, probably, in an open interlayer BaTiO₃ metastable structure. Irrespective of the used precursor, thermal decomposition of the (Ba,Ti)-mixed metal organic above 550 °C led to the formation of a mixture of tetragonal and hexagonal BaTiO₃ polymorphs rather than cubic. The synthesized BaTiO₃ powders are characterized by a high surface area of 40 m² g⁻¹ up to 700 °C, and an equivalent particle size smaller than 25 nm. Raman spectra indicated asymmetry inside the TiO₆ octahedra of the BaTiO₃ structure.