Octahedral\nand Tetrahedral Coordination Influences\nthe Ordering of Oxygen Vacancy Channels in SrCoO<sub>2.5</sub> and\nSrFeO<sub>2.5</sub> Thin Films

In this study, we explore how the orientation of oxygen\nvacancy\nchannels (OVCs) in SrFeO<sub>2.5</sub> and SrCoO<sub>2.5</sub> thin\nfilms is influenced by the metal–oxygen bonds in their octahedral\nand tetrahedral coordination environments. Using density-functional\ntheory (DFT) calculations, we found that energy changes due to applied\nstrain are driven primarily by the octahedral Fe–O bonds in\nSrFeO<sub>2.5</sub>, leading to a strain-induced transition between\nperpendicular and parallel OVCs relative to the substrate. In contrast,\nthe tetrahedral Co–O bonds in SrCoO<sub>2.5</sub> primarily\ndrive energy changes due to applied strain, resulting in a parallel\nOVC orientation regardless of the strain state. These computational\nfindings are supported by experimental results obtained through molecular\nbeam epitaxy (MBE) synthesis, X-ray diffraction (XRD), and scanning\ntransmission electron microscopy (STEM) analysis. Our research underscores\nthe critical role of metal–oxygen coordination environments\nin predicting and tailoring the properties of strained complex oxide\nthin films, providing a comprehensive understanding of the mechanisms\ngoverning vacancy ordering in brownmillerite structures.