The significance of temperature-dependent distributions of activation energies

While the response to an electric field of many disordered systems can be accounted for by postulating that the system contains independent particles with transition rates having a distribution of energy barriers or activation energies, in order to account for the temperature dependence of the experimental results it is often assumed that this distribution depends on temperature. In this paper, the question is examined of the minimum temperature dependence of the energies of the rates for the individual particles that is required to produce such temperature-dependent distributions for the system. This permits the clarification of the meaning of a temperature-dependent distribution of activation energies, and also shows that standard techniques such as the measurement of thermally stimulated depolarization currents often cannot determine whether or not such a distribution exists.