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

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

doi:10.1038/s41467-025-62612-1

Selective reduction in epitaxial SrFe_0.5Co_0.5O_2.5 and its reversibility

Journal Article · Fri Aug 15 00:00:00 EDT 2025 · Nature Communications

DOI:https://doi.org/10.1038/s41467-025-62612-1· OSTI ID:2584514

^[1]; Seo, Yu-Seong ^[2]; ^[3]; ^[4]; ^[1]; ^[1]; ^[5]; ^[5]; ^[6]; ^[7]; ^[4]; ^[1]; ^[1]

Pusan National University, Busan (Korea)
Sungkyunkwan University, Suwon (Korea)
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Hokkaido University, Sapporo (Japan)
Gachon University, Seongnam (Korea)
Pohang University of Science and Technology (Korea)
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

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_0.5Co_0.5O_2.5 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 Co^2.91+ to Co^2.00+. 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.

View Accepted Manuscript (DOE)

Research Organization:: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Organization:: National Research Foundation of Korea; USDOE Office of Science (SC)

Grant/Contract Number:: AC02-05CH11231

OSTI ID:: 2584514

Journal Information:: Nature Communications, Journal Name: Nature Communications Journal Issue: 1 Vol. 16; ISSN 2041-1723

Publisher:: Nature Publishing GroupCopyright Statement

Country of Publication:: United States

Language:: English

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