Dynamic Processes of Oxygen Ion Exchange in Strontium Cobaltite Bilayer Thin Films Driven by Oxidation and Reduction

Transition metal oxides (TMOs) possess variable oxygen stoichiometry which can be the cause of distinct changes to physical and electronic properties. As an example, the well-studied TMO strontium cobaltite (SrCoO_x), has two structurally and electrically distinct phases – the insulating orthorhombic brownmillerite (SrCoO_2.5– BM-SCO) and conducting cubic perovskite (SrCoO_3-δ– PV-SCO) – that reversibly transition via a topotactic pathway with the insertion or removal of oxygen. In the thin film form, this topotactic transition occurs while preserving high quality epitaxial films, making this material system of interest for ionotronic devices. Here, BM-SCO/PV-SCO (001) (15 nm/15 nm) heterostructures on strontium titanate (STO) (001) and the exchange of oxygen ions across this bilayer are investigated in order to understand changes to the interface under oxidizing and reducing conditions.[1] X-ray diffraction (XRD) and X-ray photon correlation spectroscopy (XPCS) studies reveal strongly asymmetric behavior with slower dynamics appearing during reducing versus oxidizing conditions and similar dynamics in the SrCoO_2.5 layer as compared to those near the heterointerface. Our results demonstrate a stable and reversible heterointerface, showcasing SrCoO_x as a model system for study of ionotronic behavior.<br/><br/>*Work supported by the Department of Energy, Office of Science, Basic Energy Sciences under contract no. DE-AC02-06CH11357.<br/>[1] Wenderott, et al. Adv. Mater. Interfaces 2023, 10, 2300127.