Conductivity properties of Rb3H(SeO4)2 crystals in the region of superionic phase transition

The dielectric/impedance spectra of Rb3H(SeO4)2 crystals has been studied in room- and high-temperature phases in wide frequency range. The original method of calculation of the distribution function g(τ) of relaxation times is applied for the ionic conducting materials. The high-frequency impedance spectrum splits into two relaxators by one order of magnitude at high temperatures. The calculated mean time for fast relaxation is 5.5 · 10−9 s at Tc = 450 K. The slower relaxation time is about ten times longer in the superionic phase. The difference between the faster and the slower relaxation times at high temperatures corresponds to the proportion of the rate of the proton transfer within hydrogen bond and that of the rotational hopping. The appearance of the two peaks in g(τ) confirms the two-stage transport mechanism in the hydrogen-bonded system and supports the theoretical suggestions of the important role of interproton interactions and the polaronic effect in superionic phase transition mechanism.