Hopping electronic conduction and long-term relaxation of an electret state in disordered dielectrics

The paper presents the results of investigating the isothermal relaxation of an electret potential difference U_e which is due to the screening of the surface charge of injected carriers in the bulk of a dielectric. Considering the hopping transport mechanism it can be explained why the decay time of U_e is much greater than the Maxwell relaxation time. The suggested model allows one to determine from experimental data some important parameters of disordered dielectrics. Among these parameters are the density of localized electrons, the scattering of localized electronic states in energy and Fermi level energy. Experimental data for U_e vs. time dependence for amorphous tantalum oxide are compared with those predicted from the model