Space charge trapping in electrical potential well caused by permanent and induced dipoles

Space charge formation in low-density polyethylene film containing a small amount of MgO nanoparticles (LDPE/MgO nanocomposite film) subjected to a high electric field greater than 100 kV/mm has been studied using an improved pulsed electroacoustic (PEA) system. No marked space charge formation was observed in LDPE/MgO nanocomposite films. To discuss the mechanism of no space charge accumulation in LDPE/MgO nonocomposite film, we assumed that both electric potential wells produced by a permanent dipole moment such as that of a carbonyl radical (C=0) and an induced dipole consisting of MgO nanoparticles (spherical dielectrics) under a high electric field create a trapping site for electric charge carriers. The trapping depth created by the permanent dipole moment such as that of the carbonyl radical (C=0) of chemical impurity defects is about 0.45 eV. However, that induced by high-permittivity dielectric nanoparticles is about 1.5 to 5.0 eV, which is much deeper than that of chemical impurity defects. The suppression of space charge formation is explained using the potential well model consisting of an induced dipole by a high-permittivity dielectric nanoparticle.