Normal and anomalous thermally stimulated currents and space charge in polypropylene

The short-circuit thermally stimulated discharge (TSD) currents for isotactic commercial grade polypropylene (PP) foil thermoelectrets, poled under different field and temperature conditions, indicate the distribution of traps in energy. Anomalous TSDCs flowing in the same direction as the charging current, observed in electrets poled above 100°C, are attributed to injected space charges and the blocking condition of the electrodes. Experimental data indicate that as the carrier mobility increases with the temperature and as the density of injected space charge increases with the applied field, a high charging field and a high temperature result in a high rate of return of carriers to the injecting electrode