High field dielectric properties of EB irradiated crosslinked polyethylene films in high temperature region

We have already reported that tan δ of nonpolar polymeric films, such as low density polyethylene (LDPE), becomes larger in its value and has a large electric field dependence in the high temperature region above about 50degC. Assuming the conductivity due to mobile carrier σX in high-field and high-temperature region has a small frequency dependence, we concluded that dielectric loss in this region is mainly dominated by carrier motion like DC conduction. To investigate this mechanism further, DC absorption current and electric field dependence of tan δ were measured for electron beam irradiated crosslinked polyethylene (IR-XLPE) and LDPE. The electric field dependence of σX derived from tan δ in high temperature region elucidated following results: (1) The slope of the electric field dependence of σX comes to coincide with that of σDC at 80degC and above. (2) The electric field dependence of σDC seems to fit better with Schottky model than with Poole-Frenkel model in high field region. Although the carrier generation seems to follow the Schottky model, the AC conduction mechanism is not straightforward. (author)