Anomalous Interface and Surface Strontium Segregation in (La_1–ySr_y)₂CoO_4±δ/La_1–xSr_xCoO_3−δ Heterostructured Thin Films

Heterostructured oxides have shown unusual electrochemical properties including enhanced catalytic activity, ion transport, and stability. In particular, it has been shown recently that the activity of oxygen electrocatalysis on the Ruddlesden–Popper/perovskite (La_1‑ySr_y)₂CoO_4±δ/La_1–xSr_xCoO_3−δ heterostructure is remarkably enhanced relative to the Ruddlesden–Popper and perovskite constituents. Here we report the first atomic-scale structure and composition of (La_1–ySr_y)₂CoO_4±δ/La_1–xSr_xCoO_3−δ grown on SrTiO₃. We observe anomalous strontium segregation from the perovskite to the interface and the Ruddlesden–Popper phase using direct X-ray methods as well as with ab initio calculations. Such Sr segregation occurred during the film growth, and no significant changes were found upon subsequent annealing in O₂. Our findings provide insights into the design of highly active catalysts for oxygen electrocatalysis.