Redox-Driven Nanoscale Topotactic Transformations in Epitaxial SrFe0.8Co0.2O3−x under Atmospheric Pressure

Oxygen ion exchanges at the surface of transition metal oxides have been extensively studied for understanding their nanoscale ionic behavior as well as for realizing multifunctionalities such as exotic magnetism, insulator-to-metal transition, band gap tuning, etc. To activate this exchange behavior, in many cases extreme conditions such as high temperature, high electric fields, and high vacuum are often required. These conditions have blocked the promising materials from being applied on real devices such as solid-oxide fuel cells and other electrochemical devices. In this article, we show that redox-driven reversible topotactic transformation in epitaxial $\mathrm{Sr}{\mathrm{Fe}}_{0.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_{3\text{−}x}$ thin films can be achieved at low temperature and at atmospheric pressure. This transformation triggers changes in electronic structures as well. These reversible redox reactions and/or associated changes at low temperature and under atomospheric pressure are particularly needed to develop a cathode for low solid-oxide fuel cells.