Oxygen-Stoichiometry-Driven Phase Reconstruction and Multifunctional Responses in Epitaxial Strontium Cobaltite Thin Films

Oxygen stoichiometry critically governs the phase stability and physical properties of transition-metal oxides, yet a unified understanding of how oxygen-stoichiometry-driven phase reconstruction underlies the cooperative evolution of multiple physical properties in SrCoOx remains lacking. Here, high-quality epitaxial brown millerite SrCoO2.5 and perovskite SrCoO3−δ thin films were grown by pulsed laser deposition under controlled oxygen conditions. Their structural, magnetic, electrical, optical, and photocatalytic properties were systematically compared. SrCoO2.5 exhibits antiferromagnetic insulating behavior, infrared-dominant transmittance, and higher photocatalytic activity, whereas SrCoO3−δ shows ferromagnetism, much lower resistivity, and strong optical opacity. First-principles calculations reveal that oxygen-stoichiometry-driven phase reconstruction strongly modifies the electronic structure, accounting for the distinct magnetic, transport, and optical responses. These results establish a direct correlation between oxygen stoichiometry, structural transformation, and multifunctional properties in SrCoOx, highlighting oxygen-vacancy ordering as an effective route to tailoring correlated oxide functionalities.