Processing strategies to control grain growth in ZnO based varistors

Development of functional microstructure during sintering in ZnO based varistors will determine its electrical properties. Particularly influenced is the nominal breakdown voltage of the ceramic device, since it is directly related to the ZnO grain size. Bi2O3-doped ZnO varistors sinter in the presence of a liquid phase which enhances grain growth. Addition of antimony oxide, however, leads to the formation of a spinel type phase Zn7Sb2O12, which inhibits grain growth. Both phases are formed through reactions that take place during the sintering process. In the present work, different sintering strategies are performed in order to modify these reactions, so affecting the kinetics of grain growth and hence the electrical properties from that derived.