Characteristics of thermally stimulated depolarization phenomena in zinc-oxide ceramics for varistors

The results of experimental investigations and an analysis of the temperature dependences of the thermally stimulated depolarization current are presented for zinc-oxide ceramics suitable for use in high-voltage varistors. A model for the depolarization phenomena is proposed that takes into account charge exchange on localized electronic states on both sides of the intercrystallite potential barrier. The model is used to obtain estimates of the ionization energy and density of shallow (∼0.07 eV, 1×1017 cm−3) and deeper (∼0.2 eV, 1×1018 cm−3) bulk levels and surface-localized levels (∼0.1 eV, 1×1013 cm−2).