Diffusional mass transport in ionic conductors needs to reach equilibrium state. Although thin samples of micrometers can reach equilibria in a couple of seconds or minutes, thicker samples should be kept for a longer time to reach equilibrium. Therefore, the experiments were carried out after the necessary relaxing time to reach equilibrium. The time to reach equilibrium, 𝜏, is a function of sample thickness, 𝑙, and chemical diffusion coefficient of the mobile species 𝑖 with 𝑛 ± oxidation state, D OE 9 %± , which according to Thangadurai and Weppner , in the absence of the electrical field, can be estimated by