Selective reduction in epitaxial SrFe0.5Co0.5O2.5 and its reversibility
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 L-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.
Authors
- Sangkyun Ryu (ORCID: https://orcid.org/0000-0003-4817-538X)
- Krishna Chaitanya Pitike (ORCID: https://orcid.org/0000-0002-8225-9897)
- Sangmoon Yoon (ORCID: https://orcid.org/0000-0001-6370-1320)
- Gowoon Kim (ORCID: https://orcid.org/0000-0002-5803-839X)
- Valentino R. Cooper (ORCID: https://orcid.org/0000-0001-6714-4410)
- Su Ryang Park
- Hiromichi Ohta (ORCID: https://orcid.org/0000-0001-7013-0343)
- Younghak Kim (ORCID: https://orcid.org/0000-0002-4237-0849)
- Yu‐Seong Seo (ORCID: https://orcid.org/0000-0003-3870-1112)
- Joonhyuk Lee (ORCID: https://orcid.org/0000-0001-6014-3319)
- Hee-Sun Chung (ORCID: https://orcid.org/0009-0005-8300-8204)
- Jinhyung Cho (ORCID: https://orcid.org/0000-0002-7365-8669)
- Hyoungjeen Jeen
Institutions
- Pohang University of Science and Technology (KR)
- Gachon University (KR)
- Oak Ridge National Laboratory (US)
- Pacific Northwest National Laboratory (US)
- Hokkaido University (JP)
- Pusan National University (KR)
- Sungkyunkwan University (KR)
Publication Details
- Journal
- Nature Communications
- Published
- 2025-08-15
- DOI
- https://doi.org/10.1038/s41467-025-62612-1
- Citations
- 1
- Primary Topic
- Magnetic and transport properties of perovskites and related materials
- Type
- article
- Field-Weighted Citation Impact
- 0.43
Funders
- U.S. Department of Energy
- National Energy Research Scientific Computing Center
- National Research Foundation
- Korea Basic Science Institute
- National Research Foundation of Korea
- Ministry of Science and ICT, South Korea
- Office of Science
- Joint Research Centre
- Japan Society for the Promotion of Science
- Basic Energy Sciences