Influence of phase transitions on the ionic conductivity of protonic superconductors

The temperature dependence of the proton conductivity in protonic superconductors MHAO₄ and M₃H(AO₄)₂ (M=K,Rb,Cs,NH₄; A=S,Se) is calculated for low-conducting phases near the phase-transition temperature. The observed deviations from the Arrhenius law in the temperature dependence of the conductivity below the phase-transition temperature can be explained by taking into account three facts: (1) the influence of the ferroelectric ordering, (2) the first-order character of the phase transition, and (3) the propagation of protonic defects. The study is based on using an exact solution of the equation of motion for the applied model.