Kohlrausch relaxations: new aspects about the everlasting story

For transient, time dependent polarization processes stretched exponential functions and power laws referred to as Kohlrausch relaxations are often observed in disordered dielectrics. These relaxations can be distributed in time or frequency over more than 12 decades. Among the various existing models for an interpretation two of them based on similar mathematics but different physical grounds are repeated. In these models charges, either electrons or protons, hop between adjacent sites. The distances between the sites are distributed resulting in a distribution of relaxation times. Then two new models which emerged in the last years are discussed. (I) It is shown that the dipolar interaction between dipoles of the same kind, i.e. without a distribution of any property, can result in Kohlrausch relaxations. (II) In solid electrolytic capacitors charges can be attracted by their images in the electrode. After application of an external voltage this charge attraction leads to an external current with a power law time dependence. Index Terms--Insulators, dielectric polarization, relaxation processes, Monte Carlo methods, distribution function, dipolar interaction, electrodes, Kohlrausch relaxations.