Temperature dependence of quasi-ferroelectric hysteresis in a model ferroelectret system

Non-uniform dielectric materials or materials systems with foam structure can be rendered piezoelectric by internal charging of their cavities through a series of dielectric barrier discharges (DBDs). DBDs inside the cavities lead to phenomenological hysteresis curves that can in principle not be distinguished from those on other ferroic materials. Here, the influence of the gas temperature on the hysteresis loops of ferroelectrets has been studied over a wide temperature range from -100 to +140°C. In order to minimize temperature-induced changes in the geometry of the cavities and in the charge-storage behaviour of the dielectric, mica sheets were employed for assembling the ferroelectret systems. The coercive voltage and the effective polarization of the mica ferroelectret samples were determined as functions of the temperature of the sample and its gas-filled cavities. The results are discussed with respect to Paschen's law for electric breakdown - taking into account the respective gas temperature. It is shown that the threshold voltage decreases with increasing temperature. Therefore, the charging or poling temperature is an important parameter that strongly affects the phenomenological coercive field and the remanent polarization of ferroelectrets. The results should be taken into account when optimizing the charging process of ferroelectrets.