Dynamic processes 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. One such 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 resistive memory switching applications. Here, BM-SCO/PV-SCO (001) (15 nm/15 nm) heterostructures on strontium titanate (STO) (001) are investigated in order to understand changes to the interface between the two phases under oxidizing and reducing conditions. X-ray diffraction (XRD) and X-ray photon correlation spectroscopy (XPCS) studies reveal oxidizing conditions coupled with heating to ~250 °C led to measurable dynamics associated with changes to the PV-SCO phase as it accommodates oxygen into its lattice. Understanding gleaned from the nature and dynamics of these processes are relevant to the development of more controlled switching in these epitaxial heterostructure devices.