Metal citrate polymerized complex thermal decomposition leading to the synthesis of BaTiO3: effects of the precursor structure on the BaTiO3 formation mechanism

The study of BaTiO3 crystallization from X-ray amorphous (Ba,Ti) polymeric organic powders has been carried out by comparing samples previously heat-t reated in air at 250 and 400 degreesC. From thermal analysis, X-ray diffrac tion, infrared and Raman spectroscopies, and C-13 NMR spectroscopy, it has been found that the BaTiO3 formation strongly depends upon the initial stru cture of the used precursor. It is concluded that an intermediate oxycarbon ate phase was formed prior to the formation of BaTiO3 above 550 degreesC wh en the precursor used was a (Ba,Ti)-mixed metal organic complex heat-treate d at 250 degreesC, and a nanocrystalline BaCO3 intermediate when the metal organic complex had been initially heat-treated at 400 degreesC. Although n ot 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 B aCO3 located, probably, in an open interlayer BaTiO3 metastable structure. Irrespective of the used precursor, thermal decomposition of the (Ba,Ti)-mi xed metal organic above 550 degreesC led to the formation of a mixture of t etragonal and hexagonal BaTiO3 polymorphs rather than cubic. The synthesize d BaTiO3 powders are characterized by a high surface area of 40 m(2) g(-1) up to 700 degreesC, and an equivalent particle size smaller than 25 nm. Ram an spectra indicated asymmetry inside the TiO6 octahedra of the BaTiO3 stru cture.