Electron Microscopic Investigation of Post-Annealed Superconducting GdBa$_2$Cu$_3$O$_{7-δ}$ Thin Films on MgO

GdBa$_2$Cu$_3$O$_{7-δ}$ (GdBCO) is a promising high-temperature superconductor with potential application as coated conductor for power applications (e.g. transformers). However, further improvements in cost-effectiveness and superconducting properties are desired. The latter are influenced by O content, film texture, and film quality, where non-superconducting defects can effectively pin magnetic flux lines if they have favorable shape, size, and density. The O content in GdBCO can be set in-situ after film deposition or afterward by annealing in a different furnace (ex-situ). The correlation of oxygenation processes and defect formation/healing in GdBCO is not fully understood. In this work, we apply scanning transmission electron microscopy (STEM) to investigate the effect of different ex-situ oxygenation routes on the GdBCO microstructure.