Low energy electron conduction in insulators

The electrical conduction due to trapped electrons with energy higher than the potential barrier (Poole-Frenkel effect) is claimed to take part in several materials /1/. Much less is known about the current due to electrons whose energy is lower than the trapping well. A classical model is here formulated to take into account such contribution and the theoretical results are compared with those experimentally obtained in CdF 2: Gd crystals.