Determination of Dielectric Behavior at Low Frequencies from Measurements of Anomalous Charging and Discharging Currents
The relation between anomalous charging or discharging currents and ac dielectric behavior of a material is discussed together with the use of the Hamon approximation for calculating the loss factor from these currents. The validity of the assumption used in deriving the Hamon approximation is discussed with reference to the behavior of a material with a Cole-Cole distribution of relaxation times. An analytical derivation of the Hamon approximation which has appeared in the literature is described together with a discussion of the limits of its validity. A description of the experimental methods which have been used to measure these anomalous currents (dc transient technique) is given, and experimental data in the literature showing the continuity of the loci of relaxation processes and values of loss factor from the audio frequency region into the very low-frequency region (e.g., 10-4 to 10-2 cps) is discussed. Solids often have long relaxation times at ordinary temperatures and are then suitable for examination with the dc transient technique. Moreover, the components of loss due to relaxation and conduction may be separately determined using this technique, and this is an essential prerequisite to an understanding of the different mechanisms involved. When peaks in loss factor are obtained, all the usual dielectric information may be obtained-including distribution of relaxation times, activation energy and entropy for dipole orientation, and dipole-moment values for the structural units involved.