A research group from the AGH University of Krakow, specializing in material chemistry, in collaboration with the SOLARIS Center, has published findings on the impact of phase symmetry in the CaTiO3 – SrTiO3 perovskite system on the incorporation of cobalt into the perovskite structure. These cobalt-modified materials are promising for applications in energy conversion technologies and environmental catalysis. The findings, published in Materials Chemistry and Physics, revealed distinct behaviors between calcium-rich (Ca-rich) and strontium-rich (Sr-rich) perovskite materials. The study also examined the impact of non-stoichiometry on both, the position occupied by cobalt in the structure and its oxidation state. A comprehensive understanding of the structural changes in the system was achieved through an innovative approach combining X-ray absorption spectroscopy (XAS) analysis, conducted at the ASTRA beamline, with results from temperature-programmed reduction (TPR) studies.
Ca-rich materials, characterized by orthorhombic symmetry, more effectively incorporate cobalt into the perovskite structure but also tend to form a secondary phase – CoTiO3. In contrast, Sr-rich materials with tetragonal symmetry predominantly lead to the formation of cobalt oxides, particularly Co3O4. The slight deviations from stoichiometry (a deficiency of atoms in the Ca/Sr sublattice) intensify these effects: in Ca-rich materials, they increase the proportion of the CoTiO3 phase in the system, while in Sr-rich materials, they result in a higher content of cobalt oxides. Additionally, XAS and TPR results revealed that Ca-rich materials contain more cobalt in the +II oxidation state, while Sr-rich materials contain more cobalt in the +III oxidation state.
These findings open new possibilities for designing materials and optimizing their properties for potential applications in catalysis and electrochemical devices. At the same time, they significantly enhance the understanding of solid-state chemistry, particularly the chemistry of materials with a perovskite-type structure.
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