Space charge formation in LDPE/MgO Nano-composite under high electric field at high temperature

Time dependence of space charge formation under high dc electric field at various temperatures between 30 and 60degC in nanocomposite of low density polyethylene (LDPE) mixed with nano-size filler of magnesium oxide (MgO) were studied using pulsed electro-acoustic (PEA) method. In LDPE without MgO, it is found that huge amounts of both positive and negative packet-like charges injection at all measured temperatures, and they makes a local electric field in bulk higher. On the other hand, there is almost no such huge packet-like charge was observed in LDPE/MgO with MgO content of more than 1 phr even under high electric field at high temperature, while it was observed in that with MgO content of 0.2 phr. To study the reason of such space charge suppression effect by nano-filler, we tried to calculate the potential distribution which is induced by the difference of relative permittivities between LDPE and MgO under such high electric field. By a numerical analysis, it is found that the induced potential distribution induced around the nano-filler under high electric field works as a deep trap to capture and to prevent the movement of injected carriers from electrode.