A new analysis of the bulk ac electrical response of ionic conductors

Measurements of the bulk ac electrical response of the fluorine ion conductor (1 - x)CdF(2)xErF(3), x = 0.15, are shown to be composed of separable dipolar dielectric and hopping conductive components. The dielectric component has a relaxation frequency of similar to 4 kHz and power law, Cole-Davidson frequency dependencies of real and imaginary parts. The conductive component is frequency independent up to similar to 100 kHz and decreases in a Drude fashion at higher frequencies. Ion hopping, characterised by a narrow exponential distribution of activation energies, is shown to generate the measured electrical responses. A model is proposed in which the dielectric component is identified with ions associated with immobile counter-ion or defect clusters and the conductive component with ions at lower activation energy sites between the clusters. It is found that a quantitative account of the conductivity can be obtained by assuming it to arise from a percolation fraction of the ions. (C) 1998 Elsevier Science B.V. All rights reserved.