Protonic conductivity and phase transition in K1 − x(NH4)xHSO4

Temperature dependence of the dc conductivity has been investigated in the solid solution K 1 − x(NH4) xHSO4 for several x at temperatures 300 K ≤ T ≤ 400 K. In spite of the fact that each constituent compound is not a superprotonic conductor, the samples with x = 0.15, 0.37, 0.5 and 0.72 show the typical superprotonic phase transition. The best Arrhenius fits of the conductivity in the superprotonic phase provide the activation energies ranging from 0.37 to 0.49 eV. For the low conducting phase they are between 0.79 and 0.59 eV. The complex modulus of each sample is well described by a sum of two Cole–Cole type modulus functions. One of the two relaxation processes associated with the two modulus functions has the peak frequency which is nearly the same as the conductivity in its temperature dependence. It is suggested that the coupled reorientation of NH4+ and HSO4− is the most probable origin of those two relaxation processes.