Multi-level ionic conductivity in Ca-doped BiFeO₃ thin films

Ca-doped bismuth ferrite is a promising material for studying collective ionic migration in solids [1]. We conduct impedance analysis with different magnitudes of AC voltage to understand the ionic conduction mechanism of this material. To suppress the electronic contribution to the conductivity, we annealed the sample in a reducing condition at elevated temperatures before the measurement. By using the mixed conductor equivalent circuit model [2], we obtain ionic conductivity, which shows a multi-level feature. This result shows consistency with the observation from electroforming experiments with DC voltages. This work provides useful insight into the ionic conduction mechanism in solids.