New model for nearly constant dielectric loss in conductive systems: Temperature and concentration dependencies

By appropriate fitting of conductive-system frequency-response data for two different ionic materials over ranges of temperature and ionic concentration, it is shown how dispersion associated entirely with ionic motion and that leading to nearly constant dielectric loss (NCL) can be unambiguously distinguished and separated. The latter is clearly associated with polarization of the bulk material, and in the limit of zero mobile-ion concentration NCL appears to approach zero, yielding only a bulk dielectric constant, epsilon(Dinfinity0), one that is frequency-independent over the usual immittance-spectroscopy experimental range. For nonzero ionic concentration, however, dielectric NCL appears and can be represented by a small-exponent constant phase element (CPE) complex power law in frequency. This part of the full response may be modeled either by a CPE that includes all bulk dielectric dispersion or, more plausibly, by epsilon(Dinfinity0) and a CPE representing only incremental bulk dispersion associated with coupling between ionic motion and bulk polarization. In this case, interestingly, precise power-law dependencies of various dielectric parameters on ionic concentration are established but need theoretical explanation. Fitting of the ionic part of the total dispersion with three different Kohlrausch-Williams-Watts models leads to dependencies of their different beta-shape parameters and dielectric quantities on temperature and on ionic concentration and strongly suggests that the widely used original-modulus-formalism dispersion fitting model is incorrect and should be replaced by a corrected version. (C) 2002 American Institute of Physics.