Electric Conductivity and Proton Motion below Superionic Transition on Rb₃H(SeO₄)₂

Abstract

We have studied the proton motion below the ferroelastic-paraelastic phase transition (superionic transition) temperature T_c=449 K from the NMR absorption lines. From the analysis of the NMR absorption lines, it was found that the second moment changes drastically in the temperature region from 340 K to 420 K. Moreover, we obtained the result that even below T_c the correlation time of proton τ_c obeys the Arrhenius relation τ_c = τ₀ exp(Δ E / kT) with τ₀=4.3 × 10^-11 s and Δ E= 0.47 eV. This activation energy is close to that of proton above T_c. Furthermore, the electric conductivity calculated with τ_c, which is obtained from the second moment of the NMR absorption lines, was compared with the experimental one. The result indicated that proton motion plays an important role in the electric conductivity even below T_c.