To study the local structure and oxygen ion conduction mechanism in (La0.6Sr0.4)(Co0.2Fe0.8)O3−δ (LSCF) as a function of the oxygen partial pressure (P(O2)), in situ the Co and Fe K-edge X-ray absorption spectroscopy (XAS) was measured at elevated temperatures of 900 and 1000 K. The reduction of the Co and Fe valence, i.e., the oxygen content (3−δ) in LSCF, followed the change of P(O2) from 1 to 10−4 atm during∼4000 s. The quantitative analysis of the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) indicated that the Fe valence was higher than the Co valence at oxidative condition (δ≈0) in LSCF. Whereas the Co valence decreased more than the Fe valence after reduction of P(O2) at both 900 and 1000 K. From the relaxation plots of the valence and the oxygen content (3−δ) for Co and Fe after changing P(O2), we successfully determined Dchem and Ea of an oxygen ion migration around Co and Fe in LSCF. A structural model with and without oxygen vacancies and an oxygen ion conduction mechanism for LSCF are proposed based on these results.
Graphical abstract
A structural model with and without oxygen vacancies, and the oxygen ion conduction mechanism of LSCF were speculated. In other words, oxygen vacancies would form more preferentially around Co than Fe from the results of in situ XAS analysis during reduction, and oxygen ions needs to pass through at the vicinity of Fe from the results of Dchem and Ea.
