Electronic and structural properties of La_(0.4)Sr_(0.6)Ti_(1-y)Co_yO_(3±δ) electrode materials for symmetric SOFC studied by hard X-ray absorption spectroscopy

摘要

We present combined Synchrotron X-ray Absorption Near Edge Spectroscopy (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) study of La_(0.4)Sr_(0.6)Ti_(1-y)Co_yO_(3±δ) (0 ≤ y ≤ 0.5), which are promising electrode materials for symmetric solid oxide fuel cells. The measurements were performed at room temperature at the Ti and the Co K-edges in order to determine the local structural and electronic changes around the two transition metals. We find that Ti remains in a higher formal valence (around 4+) independent of the Co concentration. In contrast to this, dramatic and systematic changes are observed for the Co as a function of y. We conclude that the stability of the Ti~(4+) triggers the A-site deficiency in our samples and predicts that oxygen vacancies are much more easily formed at large Co content, which in turn will greatly enhance the performance as electrode material.