Microstructural and electrical properties of flash sintered ZnO-Bi2O3-Sb2O3 based varistors: Effect of current density with a controlled current ramp

The ZnO-Bi2O3-Sb2O3-based varistors were produced by the flash sintering method. The effects of current density passed through the sample during the sintering process on the microstructure, and electrical properties of Varistors were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), impedance spectroscopy, and electrical measurements. The average grain size increased from 1.46 mu m to 4.85 mu m by increasing the current density from 80 to 200 mA/mm2, respectively. The XRD analysis showed that the pyrochlore phase was decomposed in the samples sintered by the current density of 200 mA/mm2. Increasing the current density passed through the sample during the flash sintering process resulted in the modified nonlinear characteristics of varistors. The highest relative density (94% of theoretical density) and the optimum electrical properties were obtained in varistors sintered by 200 mA/mm2, i.e., the nonlinear coefficient, leakage current density, and Schottky barrier height of 39.1, 12 mu A/cm2, and 0.43 eV, respectively.