The effect of composition on flash sintering parameters of varistors based on ZBS

Flash sintering is one of the latest sintering processes of ceramics, which has recently attracted the attention of researchers due to its high sintering speed and significant energy reduction. An essential feature of successful flash is negative temperature coefficient (NTC) semiconductor behavior. In this research, the flash sinter process of ceramic varistor based on ZnO-Bi2O3-Sb2O3 (ZBS) has been investigated and the effect of changing the molar ratio of the compound and adding cobalt oxide (Co3O4) as an increasing factor of electrical conductivity has been studied. The optimal conditions of the flash process were determined by applying different values ​​of electric field and current density, and finally, the electric field was 300 V/cm and the current density was 100 mA/mm2. The structural investigation and identification of the formed phases have been done by scanning electron microscope and X-ray diffraction, respectively. The electrical characteristics of the varistor (non-linear coefficient, breakdown voltage, and leakage current) were measured under the DC electric field. The density of the sample with cobalt oxide additive was 97% of the theoretical density. SEM results indicate the formation of varistor microstructure with an average grain size of 3 microns. By determining the electrical characteristics, the behavior of the varistor was observed, in which the nonlinear coefficient was 22, the threshold voltage was 4500 V/cm and the leakage current density was 50 μA/mm2.