Dopant Effects to Pores in ZnO Varistors

Pore is an intrinsic property of ZnO varistor. There are two different shapes of pores in ZnO varistor samples, one is sphere shape, and another is irregular polyhedron. Pores are caused by air particles wrapped in initial varistor compact and grains-surrounded spaces during the sintering. By analyzing the pore phenomena in two different systems of ZnO varistors, we observed the pore ratio decreases, pores with large size are formed, and the pores inside ZnO grains decreases with the increase of the amount of Al
₂
O
₃
additives, which are caused by the pinning effect of spinel formed by additives. The pores are possibly related to grain growth inhibition by dragging effects