Optimizing the Proton Conductivity with the Isokinetic Temperature in Perovskite‐Type Proton Conductors According to Meyer–Neldel Rule

Abstract Perovskite‐type metal oxides such as Y‐doped BaMO₃ (M = Zr/Ce) have drawn considerable attention as proton‐conducting electrolytes for intermediate temperature ceramic electrochemical cells. Improving the proton conductivity at lower temperatures requires a comprehensive understanding of the proton conduction mechanism. By applying high pressure or varying the Ce content of Y‐doped BaMO₃, it is demonstrated that the proton conductivity follows the Meyer–Neldel rule (MNR) well. In the Arrhenius plot, the conductivities intersect at an isokinetic temperature, where the proton conductivity is independent of activation energy. Considering the relationship between isokinetic temperature and lattice vibration frequency, a high isokinetic temperature is observed in materials with stiff lattices, consisting of light atoms and small MO bond length. Based on consideration of the MNR, it is suggested that the enhancement of proton conductivity at low temperature can be well achieved by tuning lattice vibration frequency toward a desired isokinetic temperature.