Empirical relationships for ion conduction based on vibration amplitude in perovskite-type proton and superionic conductors

For superionic and deformed perovskite-type H+-ion conductors, empirical relationships among atomic mass of host or substituted ion, H+-ion conductivity, σPR, activation energy, transition temperature Tc, etc. are proposed. We elucidate the roles of heavy host ion and specific crystal structures below and above the Tc on the H+-ion conduction by noticing a large amplitude of O-ion vibration mode arising from a large fourth order anharmonicity. We clarify the important role of strengthened ionic force for the host cation lattice at and above Tc on the H+-ion jumping, and interpret reasonably the σPR value depending on the concentration of doping ion, a large broadening of vibration band and an enhanced amplitude of OH-vibration mode, etc. We suggest the extension of this consideration to stabilized zirconium and superproton conductors, etc.