Dynamic Breakdown of ZnO Varistor Ceramics under Pulsed Electric Field

Electrical breakdown process of ceramics is a complex process related to electrical, thermal, and light effects. It has attracted lots of attentions. But the mechanism of dielectric breakdown is still under debate, especially for the solid ceramics. In this study, the ceramics with different grain size were sintered at different temperatures. A square pulsed voltage of 27 kV with the pulse width of 7 s was generated to breakdown the ZnO ceramics with a thickness of 2 mm. Electric breakdown process of these ceramics were investigated using a homemade high-timeresolution electric detection system with the resolution < 1 ns. Compared the electric behaviors of ZnO ceramics with different grain sizes during the breakdown process, it is clear that the whole electric breakdown process could be divided into three main steps, all of which can completed within 7 s. The first breakdown step is the pores breakdown due to the electric field concentration, and the second step is the grain boundaries breakdown, and then the