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A detailed study of current as a function of voltage coupled with that of the thermoelectret state has been undertaken in sisal wax. Below 65°C, Ohm's law is seen to be followed at low voltages, while at higher voltages space-charge-limited conduction following a power-law dependence of current on voltage has been observed. A complete study of the current as a function of voltage, temperature, and thickness indicates an exponential distribution of trapping states in the band gap which is found to be about 7.38-eV wide. Voltage dependence of the quasi-Fermi energy, Ef, has been shown to be consistent with the filling of an exponential trap distribution. The dependence of the initial charge densities on the polarizing field and temperature, and their decay with time have shown that the electret state is due to the localization, in different trapping states, of charges which have a double origin: the injection from the electrodes and a thermally activated production of electron—hole pairs in the bulk. The observed initial positive charge densities on one-sided metallized sisal wax samples correspond to trap densities of the order of 1012 cm−3.

A detailed study of the initial charge developed on the nonmetallized surface, coupled with that of short-circuit thermally stimulated currents (TSC), has been undertaken in breakdown-charged one-sided metallized 25 μm polystyrene foils. The observed surface charge densities are of the order of 10 −8 C cm −2 . Short-circuit TSC spectra of freshly prepared electrets show a dominant high-temperature peak and two other peaks of small magnitude at lower temperature. The polymer does not become totally discharged before reaching its softening point at 125°C. Analysis of thermally stimulated currents indicates that the electrons are subject to fast retrapping in this polymer. The largest ratios of the mean charge depth to the sample thickness, obtained for electrets depolarized soon after charging and 24 h after changing, are found to be 0.08 and 0.17, respectively. This increase is considered to be due to electron retrapping at various energy levels. The observed initial released charge densities correspond to full-trap densities of the order of 10 15 cm −3 .