Thermally stimulated current in low-density polyethylene/MgO nanocomposite - On the mechanism of its superior dielectric properties

Recently polymer nanocomposite has been attracting much attention as an emerging insulating material. In this paper, we measured thermally stimulated depolarization current (TSDC) in low-density polyethylene (LDPE)/MgO nanocomposite by changing measuring parameters such as the temperature increasing rate and the intensity of electric field applied. As a result, a TSDC peak that spreads over a wide temperature range from 0 °C to 60 °C was observed in all the samples. As the amount of MgO nano-filler increases, the TSDC peak height decreases. Furthermore, by adopting a partial heating method, the wide TSDC peak was resolved into several component peaks. Among them, the peak at around 12 °C was found not to appear in the base LDPE. By analyzing its initial rising portion, the 12-°C peak was assumed to have a fairly deep energy depth of about 2 eV. These results indicate that charge carriers tend to be captured more strongly by the addition of MgO nano-fillers. If these captured charge carriers induce homocharge layers in the vicinity of the electrodes further formation of space charge would be suppressed. This seems to explain the fact that the amount of space charge is smaller in the nanocomposite with a proper addition of MgO than in the base LDPE.