Grain Size Control in Low‐Voltage Varistors

Low‐voltage ZnO varistors often suffer from a large spread in the current/voltage characteristics, due to discontinuously grown, inhomogeneous microstructures. Addition of seed grains to the ceramic powder is an effective means of preventing the growth of single large grains, thus making the control of final grain size and electrical properties much easier. Seed grains are generally single‐crystalline particles of the same composition with a grain size which is considerably larger than the average grain size of the starting ZnO powder.