Interpreting the real part of the dielectric permittivity contributed by mobile ions in ionically conducting materials

Electrical conductivity relaxation experimental data of ionically conducting glasses, crystals, and melts are most often discussed in the context of either the real part of the complex conductivity, Re[σ*(ω)], the imaginary part of the complex permittivity Im[ε*(ω)], or the complex electric modulus M*(ω). In contrast, the real part of the complex permittivity, Re[ε*(ω)], and the contribution of mobile ions to it are seldom considered. One reason for the lack of attention to Re[ε*(ω)] is the complication caused by a large additional capacitive contribution to Re[ε*(ω)] from electrode surface polarization, making the task of separating the two contributions difficult. However, there are still many ionic conducting materials in which the electrode polarization effects can be isolated and the contribution from mobile ions, εᵢₒₙ^'(ω), determined. The frequency dispersions of εᵢₒₙ^'(ω) in several such ionic conductors are used to examine the different interpretations of the mechanism of ion conductivity.