Electric-field-induced migration of oxygen vacancy in calcium doped bismuth ferrite films

Migration of ionized oxygen vacancy in oxide materials modulates their local physical properties and functionalities. In resistive memory, electric-field-driven distribution of oxygen vacancy establish the local conducting channel or bulk conducting region. Solid oxide fuel cell can convert stored chemical energy to electrical energy via oxygen ions migration through electrolyte materials. Thus, understanding the motion of oxygen vacancies is important to design effective oxide devices and enhance their functionalities. Ca-doped BiFeO₃ (BCFO) has massive oxygen vacancies to stabilize the oxidation number of Fe³⁺ ions and suitable to investigate the motion of oxygen vacancies [1, 2]. Depletion of oxygen vacancies in BCFO results in the dark-colored region induced by hole carriers. In this study, we introduce a visualization of oxygen vacancy propagation through optical microscope during the electrical forming process. Tracing the color change of BCFO films can quantify their thermodynamic variables. Furthermore, from their thermodynamic variables, we suggest BCFO films can be one of promising material to utilize for further device.
[1] C.-H. Yang, et al. Nature Materials 8, 485 (2009).
[2] J. S. Lim, et al. Physical Review B 94, 035123 (2016)