Unravelling cobalt incorporation in Ca- and Sr-rich perovskites: How symmetry shapes the phases

The Ca-rich and Sr-rich stoichiometric and non-stoichiometric materials were obtained by the modified citrate method. After calcination at 900 °C, materials were characterized in terms of structure, microstructure and reducibility in an H₂-containing atmosphere. The diffractometric data did not confirm the presence of Co-originated phases. Co K-edge and Ti K-edge were recorded and analyzed for a deeper description of the structural properties of materials, mainly the influence of non-stoichiometry on the effectiveness of Co incorporation into the perovskite systems. The X-ray absorption near edge structure study combined with temperature programmed reduction results indicated the presence of CoTiO₃ and cobalt oxides phases for Ca-rich and Sr-rich. This approach also allowed to observe that non-stoichiometry in Sr-rich materials results in a lower amount of cobalt incorporated into the perovskite structure and a higher amount of Co₃O₄ formed. Additionally, for Ca-rich materials, XANES spectra indicated a higher amount of Co in the Ti sublattice and confirmed the higher Co²⁺/Co³⁺ ratio than in the case of Sr-rich materials.