Characterization of charge trapping/detrapping phenomena by calorimetric measurements in charged dielectrics

Dielectric behavior of insulators can be explained using the space charge physics based on the concept of polarons. The local variation of polarisability due to crystal defects is responsible for trapping charges. In polycrystalline ceramics, point and extended defects, grain boundaries or impurities are sites of trapping charges. The charge detrapping can be initiated by any perturbation and corresponds to the free energy minimization occurring when an activation barrier height is reached. Any kind of variation (for example electrical, mechanical or thermal variation) contributes to approach this barrier. So a soft relaxation of a charged dielectric can be obtained by annealing the sample with slow heating rates to avoid a rapid destabilization of the space charge leading to inevitable breakdown. In this work we have tried to investigate the effect of detrapping/trapping of the space charge on the relaxation/polarization of charged dielectrics from measurements of the heat flow as function of the temperature by differential scanning microcalorimetric method