Discrimination between series and parallel fitting models for nearly constant loss effects in dispersive ionic conductors

Abstract The important effects of electrode polarization on the conductivity of ionic materials are illustrated for both low- and high-frequency regions. Experimental data fitting and simulation with a fully complex model, including a part representing ionic dispersion and constant-phase-element (CPE) power-laws in series or in parallel, show that the series element, usually representing electrode effects, can lead to σ ′ ( ω ) log–log slopes of 1.3 or more. In addition, over a substantial frequency region, such effects can yield σ ( ω ) response indistinguishable from that following from the parallel combination of the ionic dispersion model, here a form of Kohlrausch–Williams–Watts behavior, and a CPE. With a sufficiently wide experimental frequency range, one can discriminate between these two possibilities and identify the one that is associated with the measured experimental behavior. The problem of discrimination is particularly difficult, however, for low-temperature data that show nearly-constant-loss e ″( ω ) response. In contrast to recent conclusions, such response can be modeled and well fitted with a composite model involving either a series or a parallel CPE.