The effect of sintering pressure on nonlinear properties of ZnO–polymer composite varistors

ZnO-polymer composite varistors were prepared by using hot press method at the temperature of 130 °C and different sintering pressures of 20 MPa, 40 MPa, 60 MPa and 80 MPa. Samples with the following specific mass percentage values were prepared: 92% wt. ZnO- 4% wt. PANI- 4% wt. PE. Then, the effect of sintering pressure on their electrical properties and microstructure was investigated. Study of (I-V) characteristic of the samples indicates that the increase of sintering pressure leads to increase of varistor leakage current. Moreover, it is observed that with increasing sintering pressure, electrical resistance in prebreakdown region, nonlinear coefficient, breakdown voltage and potential barrier height decrease. Results are analyzed regarding SEM micrographs of the samples. SEM micrographs of the samples show that with increasing sintering pressure, both the average grain size and inter-grain spacing decrease. Thus, both the average path which charge carriers pass between the two boundaries and electrical resistance of the samples, decrease at pre-breakdown region and leakage current increases.