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<p>Oxygen-vacancy engineering in transition metal oxides enables programmable functionalities by modulating the valence states and local coordination of constituents. Here, we report the selective reduction of cobalt ions in epitaxial SrFe<sub>0.5</sub>Co<sub>0.5</sub>O<sub>2.5</sub> thin films under reducing gas environments, while iron ions remain unchanged. X-ray absorption spectroscopy reveals an absorption edge shift of 1.65 eV in the Co <i>L</i>-edge upon reduction, and multiplet simulations estimate a decrease in the average Co valence from Co<sup>2.91+</sup> to Co<sup>2.00+</sup>. This site- and element-specific reduction leads to the formation of a structurally distinct oxygen-deficient phase stabilized by oxygen vacancies at tetrahedral sites, as confirmed by density functional theory. Optical spectroscopy reveals an increase in the bandgap from 2.47 eV to 3.04 eV, accompanied by enhanced transparency. Furthermore, simultaneous in situ diffraction and transport measurements confirm fully reversible redox-driven transitions among three phases: reduced defective perovskite, brownmillerite, and oxygen-rich perovskite phases. These findings demonstrate that selective redox control in multi-cation oxides enables the realization of chemically and functionally distinct oxygen-deficient phases.</p>

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Selective reduction in epitaxial SrFe0.5Co0.5O2.5 and its reversibility

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年8月15日

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  • Joonhyuk Lee,
  • Yu-Seong Seo,
  • Krishna Chaitanya Pitike,
  • Gowoon Kim,
  • Sangkyun Ryu,
  • Hyeyun Chung,
  • Su Ryang Park,
  • Sangmoon Yoon,
  • Younghak Kim,
  • Valentino R. Cooper,
  • Hiromichi Ohta,
  • Jinhyung Cho,
  • Hyoungjeen Jeen

摘要

Oxygen-vacancy engineering in transition metal oxides enables programmable functionalities by modulating the valence states and local coordination of constituents. Here, we report the selective reduction of cobalt ions in epitaxial SrFe0.5Co0.5O2.5 thin films under reducing gas environments, while iron ions remain unchanged. X-ray absorption spectroscopy reveals an absorption edge shift of 1.65 eV in the Co L-edge upon reduction, and multiplet simulations estimate a decrease in the average Co valence from Co2.91+ to Co2.00+. This site- and element-specific reduction leads to the formation of a structurally distinct oxygen-deficient phase stabilized by oxygen vacancies at tetrahedral sites, as confirmed by density functional theory. Optical spectroscopy reveals an increase in the bandgap from 2.47 eV to 3.04 eV, accompanied by enhanced transparency. Furthermore, simultaneous in situ diffraction and transport measurements confirm fully reversible redox-driven transitions among three phases: reduced defective perovskite, brownmillerite, and oxygen-rich perovskite phases. These findings demonstrate that selective redox control in multi-cation oxides enables the realization of chemically and functionally distinct oxygen-deficient phases.