Oxygen Nonstoichiometry and Valence State of Manganese in La_1-x Ca _x MnO_3+δ.

ABSTRACT: Perovskites of the ABO₃ type, such as LaMnO₃, can be used as air electrodes in solid oxide fuel cells and electrolyzers. Their properties can be tuned by A- and B-site substitutions. The influence of La substitution by Ca on the oxygen nonstoichiometry has been investigated frequently, but the results depend highly on the synthesis and atmospheric conditions. In this work, a series of La_1-x Ca _x MnO_3+δ (x = 0-0.5) was synthesized using conventional solid-state synthesis under an air atmosphere. The structures of the materials were studied in detail with powder X-ray diffraction. The initial oxygen nonstoichiometries were determined using thermogravimetric reduction. The samples were subsequently analyzed in terms of defect chemistry in dependence of temperature, atmosphere, and Ca content via thermogravimetric analysis. The changes in the manganese charge states were investigated by X-ray absorption near-edge spectroscopy experiments. The influence of intrinsic and extrinsic effects on the Mn-valence state of the differently Ca-substituted samples as calculated from thermogravimetric analysis and as determined directly from X-ray absorption near-edge spectroscopy is presented.

SUBMITTER: Heuer SA 

PROVIDER: S-EPMC8047706 | biostudies-literature | 2021 Apr

REPOSITORIES: biostudies-literature