Study of the relationship between the local geometric structure and the stability of La0.6Sr0.4MnO3−δ and La0.6Sr0.4FeO3−δ electrodes

Abstract

Sr-substituted ABO3 perovskite oxides such as La0.6Sr0.4MnO3−δ (LSM) and La0.6Sr0.4FeO3−δ (LSF) are widely used as oxygen electrode materials in solid oxide cells. The substituted Sr is not adequately stable under the operating conditions, because of the surface segregation of Sr. Herein, we focused on investigating the relationship between the local geometric structure due to Sr substitution and stability of LSM and LSF. We characterized the local geometric structure of Sr atoms via X-ray absorption spectroscopy. A greater Debye–Waller factor and a longer bond length of both the second and third Sr–O shells were observed in LSF, which demonstrates that LSF has a higher local structural disorder and that Sr in LSF requires less energy to segregate. After 20 h of heat treatment in the presence of a Fe–Cr alloy interconnect, the Sr/La molar ratio on LSF was observed to be much larger than that on LSM. This result unequivocally suggests that Sr in LSF is not as stable as in LSM, and the reaction between Sr and Cr accelerates the Sr surface segregation in LSF.