In-situ X-ray diffraction study of carbonate formation and decomposition in perovskite-type BCFZ

The effect of CO2 on the two phase perovskite with average composition of BaCo0.4Fe0.4Zr0.2O3-δ is investigated by in-situ X-ray diffraction (XRD) as well as transmission electron microscopy (TEM). Partial decomposition of the BCFZ into high-temperature rhombohedral BaCO3 polymorph was observed during annealing in an atmosphere, which contained 50 vol% CO2/50 vol% N2 at 1173 K. This carbonate structure is not quenchable and cannot be detected by ex-situ methods. Additionally, the reversible phase transition of BaCO3 from orthorhombic to rhombohedral to cubic at different temperatures accompanied by formation of CoO was shown by in-situ XRD and TEM. Furthermore, complete regeneration of perovskite phase was obtained after high-temperature treatment under CO2-free conditions. -- Graphical abstract: In-situ XRD of BCFZ powder in the atmosphere containing 50% CO2 and 50% N2 at different temperatures showing formation of BaCO3 and their phase transition. Display Omitted Highlights: → Partial BCFZ decomposition. → Rapid formation of rhombohedral BaCO3 after exposure of the CO2 at 1173 K. → Reversible phase transition of BaCO3. → Formation of CoO and tetragonal disordered Fe-enriched perovskite phase. → Complete regeneration of BCFZ after removing of CO2.