The Role of Polypyrrole in Electrical Properties of ZnO-Polymer Composite Varistors

Composite films on the base of ZnO with different weight percentages of polypyrrole have been prepared using the hot pressing method and their current-voltage characteristics have been studied. Results show that the films have nonlinear varistor behavior and can be used to protect sensitive circuits from 110V up to 350V overvoltages. It is found that the higher the content of polypyrrole in the varistor, the lower the breakdown voltage. Samples with higher polypyrrole content have less nonlinearity. The interesting result is that, unlike semiconductor-polyaniline based varistors, varistor hysteresis decreases through increasing polypyrrole content. Results have been analyzed with respect to SEM micrographs and XRD patterns of the samples. Energy gaps of varistors are evaluated using their UV spectra analysis regarding Tauc relation, which show that increasing polypyrrole content in varistors causes their absorption to increase and the corresponding band gap to decrease.