Direct Current Degradation and Electrophysical Properties of ZnO–Polyaniline Composites

This study investigates the electrical nonlinear properties of ZnO–polyaniline composite varistors before and after direct current degradation, as well as the influence of ZnO content variation in the composite. All samples were fabricated via the hot-pressing method at a temperature of 130°C and a pressure of 60 MPa. The results show that increasing the ZnO content reduces both the nonlinear coefficient (from 8.3 to 7.7) and the breakdown voltage (from 560 to 340 V). However, direct current degradation induced a notable rise in the nonlinear coefficient, most prominently in the 80% ZnO sample, where it increased from 8.3 to 11.1. All samples showed a slight increase in breakdown voltage (~40 V) alongside a reduction in leakage current. Microstructural analysis via scanning electron microscope reveals two distinct phases, i.e., ZnO grains and polymer-rich intergranular regions. Post-degradation scanning electron microscope analysis indicated no significant changes in ZnO grain morphology, suggesting that the observed electrical shifts are primarily linked to interfacial modifications.