Low-frequency dispersion in volume and interfacial situations

Abstract

The ubiquitous and little-understood phenomenon of low-frequency dispersion (LFD) is described and the experimental evidence for it is summarized for a variety of dielectric and semiconducting systems. Both frequency- and time-domain behaviour are reviewed and it is pointed out that very high charge densities are being stored at low frequencies. The connection between LFD and electrochemical reactions is emphasized. The physical conditions under which LFD can be seen are discussed with particular emphasis on the distinction between interfacial and volume processes. Earlier interpretations of LFD-like phenomena in terms of Maxwell-Wagner processes and fractal geometry of contacts are briefly discussed and found to be insufficient to account for the observed facts. It is concluded that there is likely to be more than one physical or physico-chemical cause giving rise to the variety of LFD phenomena observed in nature but their common feature must be a frequency independent ratio of loss to polarization. We define an “energy criterion” which gives a physical basis for the interpretation of power-law responses and on this basis we propose a new electrochemical model of very general applicability giving the correct dynamic response and having the advantage of not requiring enormous electric fields to account for the very high charge storage observed. Further critical experimental studies are required to elucidate the remaining questions.