The advantages of simultaneously plotting alternating-current data in terms of impedance, electric modulus and dissipation factor were illustrated. It was recalled that complex impedance was generally used for ionic conductors because it could easily distinguish between bulk and grain boundary effects. However, comparison with modulus and dissipation factor data permitted easier interpretation of the microscopic processes which were responsible for the measured alternating-current response. In particular, the difference between localized (dielectric relaxation) and non-localized conduction (long-range conductivity) processes within the bulk of the material could be distinguished by the presence or absence of a peak in the imaginary modulus versus frequency plot. Similarly, the absence of a peak in the imaginary impedance versus frequency plot could be correlated with space charge effects and non-localized conductivity. Long-range conductivity produced almost complete impedance semicircles, but no frequency dispersion in the permittivity, while localized conductivity was reflected by a frequency-dependent permittivity, but no measurable conductance. The degree of certainty to which these attributions could be made was related to the dielectric relaxation ratio and to differences between the time constants of the various relaxation processes which were operating in the material.

R.Gerhardt: Journal of the Physics and Chemistry of Solids, 1994, 55[12], 1491-506