Influence of filler content on traps and conductivity of epoxy resin nanocomposites
Epoxy resin nanocomposites have high resistivity and high breakdown voltage and perform excellent in suppressing space charge accumulation, which is important for the development of DC power equipment. However, how nanofiller content impacts on the resistivity of nanocomposite still remains to be unclear. Therefore, a method, based on the structure model of interaction zones, is proposed to investigate densities of deep and shallow traps of nanocomposite. Then trap densities as a function of nanofiller content is obtained. With an increase in nanofiller content, shallow trap density gradually rises up, while deep trap density shows an increase firstly and then a decrease due to the overlapping of interaction zones. Additionally, at higher nanofiller content, it is found that shallow trap density goes up quantitatively and mean-distance between shallow traps decreases rapidly, thus carriers are easier to hop and migrate in shallow traps and mobilities of carriers controlled by shallow traps increase correspondingly. Then, a charge transport model is introduced to investigate charge distribution, electric field distribution and conductivity property of epoxy/TiO2 nanocomposites. It turns out that, with an increase in nanofiller content, space charge accumulation near cathode/dielectric surface goes up firstly and is followed by a decrease, correspondingly electric field distortion in cathode/dielectric field gets strengthened firstly and weakened afterwards, and the same tendency takes places in conductivity. Actually, in bulk composites, conductivity is dominated by deep traps at lower nanofiller content, while shallow traps will gradually come to domination with increasing nanofiller content. In conclusion, experimental results are in good agreement with theoretical deduction, and method and model proposed in this paper may be applied to other occasions.
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