Effect of sintering time on microstructure and electrical properties of varistor ceramics ZnO-CoO-SLS glass

The influence of sintering time on the microstructure and electrical properties of ZnO-CoO-SLS (soda lime silica) glass varistor based ceramics has been investigated. With increased sintering time, the density of the sintered pellets increased from 5.060 to 5.644 g/cm3 resulting in an increase of the nonlinear coefficient and barrier height of the ZnO-CoO-SLS glass varistor ceramics from 6.742 to 8.252 and 0.846 to 0.955 eV, respectively. The breakdown voltage is inversely proportional to the leakage current. The breakdown voltage increases from 183.7 to 278.6 V/cm and the leakage current decreases from 5.832 to 4.324 ?A/cm2 as the sintering time is increased from 60 to 150 minutes but as the increase sintering time of 150 minutes their value decreases to 222.8 V/cm and increases to 5.078 ?A/cm2. The high nonlinearity of 7.366 with lowest leakage current of 4.324 ?A/cm2 has been achieved from the varistor sintered at 150 minutes, breakdown voltage of 278.6 V/cm and barrier height of 0.954 eV.