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

Abstract

In this study, we explore how the orientation of oxygen vacancy channels (OVCs) in SrFeO 2.5 and SrCoO 2.5 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 SrFeO 2.5 , leading to a strain-induced transition between perpendicular and parallel OVCs relative to the substrate. In contrast, the tetrahedral Co−O bonds in SrCoO 2.5 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.