Formation of metastable calcite-type barium carbonate during decomposition of (Ba,Ti)-precursors

What is it about?

(Ba,Ti)-precursor complexes, important for the production of advanced BaTiO3 perovskite-type materials, undergo structural transformations and complex reactions during their thermal decomposition. Based on XRD phase analysis, combined with Rietveld refinement of crystal structure data, and on IR analysis, the intermediate formation of calcite-type BaCO3 is evidenced, which can be explained by the stabilization of this metastable modification in the form of an oxycarbonate phase down to room temperature. Two possible processes, leading to such an oxycarbonate, are discussed: (i) partial substitution of CO3^2- by O2- in the anionic sublattice, and (ii) topotaxial formation of calcite-type structural domains of BaCO3 by templating with oxygen-deficient titanates, resulting in the oxideecarbonate intergrowth structures.

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Why is it important?

The paper shows the true nature of the Ba-Ti-intermediate phase which occurs during decomposition of (Ba,Ti) organic precursors to BaTiO3. The composition of this intermediate has been controversially discussed during the last 40 years.