Formation of metastable calcite-type barium carbonate during low-temperature decomposition of (Ba,Ti)-precursor complexes

摘要

(Ba,Ti)-precursor complexes, important for the production of advanced BaTiO_3 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 BaCO_3 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 CO_3~(2-) by O~(2-) in the anionic sublattice, and (ii) topotaxial formation of calcite-type structural domains of BaCO_3 by templating with oxygen-deficient titanates, resulting in the oxide-carbonate intergrowth structures.