Layer Resolved Cr Oxidation State Modulation in Epitaxial SrFe<sub>0.67</sub>Cr<sub>0.33</sub>O<sub>3-δ</sub> Thin Films.
basic_science · Level V
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- Record sourced from PubMed, PMID 39481117.
- Also identified by DOI 10.1021/acs.nanolett.4c03660.
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Abstract
Understanding how doping influences physicochemical properties of ABO<sub>3</sub> perovskite oxides is critical for tailoring their functionalities. In this study, SrFe<sub>0.67</sub>Cr<sub>0.33</sub>O<sub>3-δ</sub> epitaxial thin films were used to examine the effects of Fe and Cr competition on structure and B-site cation oxidation states. The films exhibit a perovskite-like structure near the film/substrate interface, while a brownmillerite-like structure with horizontal oxygen vacancy channels predominates near the surface. Electron energy loss spectroscopy shows Fe remains Fe<sup>3+</sup>, while Cr varies from ∼Cr<sup>3+</sup> (tetrahedral layers) to ∼Cr<sup>4+</sup> (octahedral layers) within brownmillerite phases and becomes ∼Cr<sup>4.5+</sup> in perovskite-like phases. Theoretical simulations indicate that Cr-O bond arrangements and the way oxygen vacancies interact with Cr and Fe drive Cr charge disproportionation. High-valent Cr cations introduce additional densities of states near the Fermi level, reducing the optical bandgap from ∼2.0 eV (SrFeO<sub>2.5</sub>) to ∼1.7 eV (SrFe<sub>0.67</sub>Cr<sub>0.33</sub>O<sub>3-δ</sub>). These findings offer insights into B-site cation doping in the perovskite oxide framework.