Octahedral and Tetrahedral Coordination Influences the Ordering of Oxygen Vacancy Channels in SrCoO_2.5 and SrFeO_2.5 Thin Films

In this study, we explore how the orientation of oxygen vacancy channels (OVCs) in SrFeO2.5 and SrCoO2.5 thin films is influenced by the metal–oxygen bonds in their octahedral and tetrahedral coordination environments. Using density-functional theory (DFT) calculations, we found that energy changes due to applied strain are driven primarily by the octahedral Fe–O bonds in SrFeO2.5, leading to a strain-induced transition between perpendicular and parallel OVCs relative to the substrate. In contrast, the tetrahedral Co–O bonds in SrCoO2.5 primarily drive energy changes due to applied strain, resulting in a parallel OVC orientation regardless of the strain state. These computational findings are supported by experimental results obtained through molecular beam epitaxy (MBE) synthesis, X-ray diffraction (XRD), and scanning transmission electron microscopy (STEM) analysis. Our research underscores the critical role of metal–oxygen coordination environments in predicting and tailoring the properties of strained complex oxide thin films, providing a comprehensive understanding of the mechanisms governing vacancy ordering in brownmillerite structures.