Dielectric Properties and Conductivity of (K,NH4)3H(SO4)2 Single Crystals at Low Potassium Concentrations

Abstract

The dielectric spectroscopy method was used to study the dielectric properties and conductivity of superprotonic single crystals (K_x(NH₄)_1−x)₃H(SO₄)₂ (x = 0.19, 0.27, 0.43)in the 0.1 Hz–10 MHz frequency range and the 223–353 K temperature interval. An analysis of experimental data was carried out using the formalisms of AC conductivity and the electric modulus. The room temperature value of DC conductivity of the studied crystals obtained from solid solutions was approximately ∼10⁻⁵ (Ω · cm)⁻¹, which corresponds to the conductivity values of the initial compounds at high temperatures. The comparable values of the activation energy of both DC conductivity and modulus spectrum suggest that protons are involved not only in the conductivity, but also in the process of electric relaxation. Modulus analysis indicated the temperature independent distribution of relaxation times and the non-Debye behavior in these materials. The temperature dependence of DC conductivity exhibits three (for x = 0.l9 and 0.27) and two (for x = 0.43) temperature intervals with different activation energies, which indicates the presence of structural transitions that cause a change in the mechanism of proton transport.