Morphological instability and mobility of the color front during the electrocoloration of perovskite oxide thin films

Visualization of dynamic processes during ionic migration in oxides can provide us opportunities for direct observation of various ionic phenomena and for understanding mechanisms of various applications that work based on ionic migration in solids. Electrocoloration is a readily accessible means of the direct observation of dynamic processes governed by oxygen ion migration. Here, we investigate the dynamic behavior of color fronts in the lateral devices of Ca-doped $\mathrm{BiFe}{\mathrm{O}}_{3}$ thin films grown on $\mathrm{SrTi}{\mathrm{O}}_{3}$ (100) substrates by recording the electrocoloration process with an optical microscope while simultaneously measuring the channel current. Voltage-dependent morphological instabilities, such as kinetic roughening of color fronts, are analyzed. We found that a significant amount of oxidation preceded the propagation of color fronts during electrocoloration and hence oxygen ionic mobility measured from the electrocoloration methods is the property of the intermediate phase, more oxidized than the pristine phase. This work provides intriguing insights into the dynamic behaviors of oxygen ions in oxides and the ionic mobility measurements with electrocoloration methods.