Dielectric Aspects of Prebreakdown Phenomena in Insulators

Experimental studies of conduction processes in various insulators at dc and ac voltages up to 50 kHz show that frequency dependent dielectric losses contribute to critical power densities Pk1 and Pk2 independently and equally to resistive losses in the insulating materials which arehar characterized by a spatially inhomogeneous charger carrier transport. The upper critical power density Pk2 marks the transition of the insulator into the prebreakdown state, since thermal equilibrium is no longer conserved. The value of Pk2 may be detected experimentally by the observation of shape-changes of current-instabilities. This is possible, however, only below frequency limits fg which are determined for all our samples. The processes of switching of conductivity, for example the Ovshinsky-effect ffect in the case of amorphous semiconductors, are phenomena which are restricted to the prebreakdown own state.