Nanoscale Imaging Studies of Cobaltite Thin Films Using X-Ray Nanodiffraction*

The perovskite (ABO₃) and closely related brownmillerite (ABO_2.5) phase of cobaltites possess a wide range of functional properties, which makes them promising candidates for solid oxide fuel cells, ionically-gated devices, and magneto-ionic devices. However, the role played by nanoscale morphology, i.e. phase separation and defects in these oxide thin films and heterostructures, remains unknown. This poster presents nanoscale imaging studies of emergent structural phases and their morphology in cobaltite heterostructures using x-ray nano-diffraction. Gd/La_0.67Sr_0.33CoO₃ heterostructures were ionically and stoichiometrically controlled via the thickness of the Gd oxygen-gettering layers. Our measurements, using the hard x-ray nanoprobe at the Advanced Photon Source, show lateral and transverse nanoscale separation of the perovskite and brownmillerite phases. These nanoscale heterogeneities were characterized and strain mapped in real space with a spatial resolution of 25 nm. Our studies provide insights into the nanoscale morphology which can be utilized to tune the macroscopic functional properties of cobaltite heterostructures.