Nanodiffraction imaging of ionically controlled phase separation in cobaltite heterostructures

Controlling ionic distribution and stoichiometry in complex oxide heterostructures has been utilized to significantly alter and tune functional properties of complex oxide thin films. Recently, deposition of a strong oxygen getter on top of an oxide thin film has emerged as a novel way to tailor oxygen stoichiometry and nanoscale functional properties. In this talk I will focus on Al/La_0.67Sr_0.33CoO₃ (LSCO) heterostructures, due to their high oxygen ion conductivity and coupled magnetic and electronic properties, which are strongly dependent on oxygen stoichiometry. This combination of properties enables ionic control over functional properties in LSCO thin films through the influence of oxygen extracting layers such as Al. We utilize x-ray nanodiffraction to directly image the nanoscale morphology and local strain states of LSCO thin films as they are transformed from the equilibrium perovskite phase to the metastable brownmillerite (BM). Our studies show the coexistence of perovskite and BM phases, with formation of narrow and extended BM filaments as a function of getter layer thickness. These studies provide a nanoscale survey of both the morphology of the phase separation and the accompanying local strain states of these features, and compares the effects of different getter layers such as Gd and Al.