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

Area of Science:

• Materials Science
• Solid-State Chemistry
• Oxide Electronics

Background:

• Oxygen-vacancy engineering in transition metal oxides allows for tunable material properties.
• Controlling valence states and local coordination is key to programmable functionalities.

Purpose of the Study:

• To achieve selective reduction of cobalt ions in SrFe_0.5Co_0.5O_2.5 thin films.
• To investigate the resulting structural, electronic, and optical property changes.
• To demonstrate reversible redox-driven phase transitions.

Main Methods:

• Epitaxial thin film growth of SrFe_0.5Co_0.5O_2.5.
• X-ray absorption spectroscopy (XAS) for valence state analysis.
• Optical spectroscopy for bandgap determination.
• In situ X-ray diffraction and transport measurements for phase transition studies.
• Density functional theory (DFT) for structural confirmation.

Main Results:

• Selective reduction of Co ions from Co^2.91+ to Co^2.00+ observed via XAS.
• Formation of a distinct oxygen-deficient phase with vacancies at tetrahedral sites confirmed by DFT.
• Bandgap increased from 2.47 eV to 3.04 eV, enhancing transparency.
• Fully reversible redox-driven transitions between perovskite, brownmillerite, and oxygen-deficient phases demonstrated.

Conclusions:

• Site- and element-specific redox control is achievable in multi-cation oxides.
• Selective reduction enables the creation of chemically and functionally distinct oxygen-deficient phases.
• Programmable functionalities can be realized through controlled oxygen-vacancy engineering.