Local structure change around Co and Fe ions in (La0.6Sr0.4)(Co0.2Fe0.8) O3-δ as revealed by in-situ X-ray absorption spectroscopy and first-principles calculation

Local structures around Co and Fe ions in (La0.6Sr0.4)(Co0.2Fe0.8)O3-delta (LSCF) with different oxygen ion content (3-delta: 2.78 similar to 3.00) were investigated by in-situ X-ray absorption spectroscopy (XAS) and first principles density functional theory (DFT) calculations. The degrees of change in the pre-edges and white lines in the X-ray absorption near-edge structure of Fe ions were greater than those of Co ions with varying 3-delta from 2.94 to 2.78 in LSCF at 1000 K. From the XAS and DFT calculations, we found that the CoO6 octahedral units remained in the rhombohedral symmetry by changing 3-delta from 2.94 to 2.78. In contrast, 30 similar to 40% of the FeO6 octahedral units changed from the rhombohedral to the cubic symmetry when decreasing 3-delta from 2.94 to 2.78. The DFT calculations also predicted that it was easier for the oxygen ions in LSCF to migrate in the FeO6 octahedral units in the cubic symmetry.