The effect of sintering temperature on ZnO varistor properties is investigated in the range of 700–1400 1C. The
increase of sintering temperature does not influence the well-known peaks related to hexagonal wurtzite
structure of ZnO ceramics, whereas the average grain size is increased from (1.08 to 2.1 mm).With increasing
sintering temperature up to 1200 1C, the nonlinear region is clearly observed in the I–V characteristics,
whereas this region is completely absent only for the sample sintered at 1400 1C. As the sintering
temperature increased, the breakdown field decreased over a wide range from 2838.7 to 6.41 V/cm,
while the nonlinear coefficient is increased in the range of (23.86–47.76). Furthermore, the barrier height
decreased from 1.76 to 0.974 eV, whereas electrical conductivity is improved. On the other hand, the optical
band gap is gradually decreased in the range of 3.08–2.70 eV with increasing sintering temperature. These
results showed a strong correlation between sintering temperature and the properties of ZnO ceramic
varistor.