Effects on the properties and microstructure of ZNO varistors

In this research, after preparation of zinc oxide nano powder via a high energy ball mill (SPEX) and evaluation of its particle size distribution, as well as morphology, by a zeta potential particle size analyzer and transmission electron microscopy, the samples were made and sintered at different temperatures. The physical and electrical properties were measured and the microstructure was studied by scanning electron microscopy. For determining the grain size distribution, X-ray diffraction analyses were also used. Finally, the I-V characteristics of the varistors were obtained with an 1-V meter (Keithley 237). It was shown that by using nano powders produced by high energy ball milling, the electrical properties of Zn O based varistors, such as breakdown voltage and the non-linear coefficient (α), were enhanced, in comparison with micro powders. The non-linear coefficient (α) was about 60 and breakdown voltage was about 5500 V/cm. The enhancement of the properties was related to the fine and homogeneous microstructures of the samples