The nonlinear conductivity and mechanism of ZnO ceramic-epoxy composite material

The nonlinear electrical properties of ZnO ceramic-epoxy composite materials with different ZnO filler concentrations were studied and the mechanisms were analyzed in this work. The electric field dependence of leakage current density was measured, which indicates that composites with ZnO filler concentration from 10 vol% to 20 vol% exhibit nonlinear electrical properties. However, the mechanisms about their nonlinear electrical properties are different. Nonlinear conductivity of composite with 10 vol% ZnO fillers appears after multiple partial discharges, which is ascribed to combination of partial discharge and tunneling effect. In order to further understand the mechanism, series resistance model of ZnO fillers and epoxy resin for conduction channel is put forward. Whereas, for the composites with 15 vol% and 20 vol% ZnO fillers, nonlinear conductivity directly appears with increasing electric field, without partial discharge, which is attributed to tunneling effect. Besides, as filler concentration increases from 10 vol% to 20 vol%, the switching field significantly drops from 380 V/mm to 56 V/mm, while the nonlinear coefficient sharply increases from 9.60 to 16.08. These results are important to clearly understand the electrical performance and mechanisms of composites for field grading materials.