Solid-state electrochemical redox control of the optoelectronic properties for SrFeO_x thin films

摘要

By utilizing redox reactions, the physical properties of several transition metal oxides can be drastically changed, which is useful for developing multifunctional memory devices. Strontium iron oxide (SrFeO_x), which exhibits a clear phase transition from antiferromagnetic insulator (x = 2.5) to helimagnetic metal (x = 3), is a good candidate for the active material in multifunctional memory devices. However, practical applications using previous demonstrations of redox reactions in SrFeO_x are limited by the use of a liquid electrolyte due to the leakage problem. Here, we demonstrate solid-state electrochemical redox reaction in SrFeO_x using a yttria-stabilized zirconia (YSZ) single-crystal substrate as the solid electrolyte. We fabricated the SrFeO_(2.5) film on the YSZ substrate and the applied electric current using Au electrodes. The phase gradually changed from SrFeO_(2.5) to SrFeO_(2.5+x) and SrFeO_(3-x). The color of the film changed from yellowish-transparent to dark brown. Although the as-grown SrFeO_(2.5) film showed high resistivity (p>10~1Ωcm), the p dramatically decreased (～10~2Ωcm) with increasing the applied charge density. Simultaneously, the thermopower greatly decreased from ～+200 to ～-10μV K~(-1). The present results would provide a design concept for future SrFeO_x-based solid-state multifunctional memory devices.