Strain-mediated insulator-metal transition in topotactically hydro-reduced SrFeO2

Controlling oxygen redox reactions in transition metal oxides offers an attractive route to tune their physical properties; a topotactic structural transformation from their parent phases effectively modifies the electronic state. In this work, infinite-layered SrFeO2 thin films were produced from brownmillerite SrFeO2.5 via low-temperature hydro-reduction. After the structural transition, their out-of-plane lattice constants dramatically shrank by similar to 12%; tensilely strained samples exhibited metallic character, whereas the compressively strained ones maintained the insulating behavior of their bulk form. According to X-ray linear dichroism results, this strain-mediated electronic anisotropy may be attributed to electron redistribution within degenerated orbitals. This suggests a possible mechanism for the metallic conductivity of infinite-layered SrFeO2, giving a hint for understanding emergent quantum phenomena, such as the recently discovered superconductivity in nickelates, and stimulating various applications, including in ionic conductivity and oxygen catalysis.

Automated summary

In this study, infinite-layered SrFeO2 thin films were successfully produced from brownmillerite SrFeO2.5 via low-temperature hydro-reduction, resulting in significant changes in lattice constants and electronic behavior. The strain-mediated electronic anisotropy may be attributed to electron redistribution within degenerated orbitals, providing insight into emergent quantum phenomena and potential applications in various fields such as ionic conductivity and oxygen catalysis.