Microstructural analysis of varistors prepared from nanosize ZnO

摘要

ZnO nanoparticles were prepared by a solid state pyrolysis reaction of zinc acetate dihydrate and oxalic aciddihydrate at 500uC. The course of reaction at various temperatures was followed by XRD. Subsequently varistorswere fabricated from this nano-ZnO material by solid state mixing with various oxide additives and sintering to1050uC. The microstructure of the sintered material was studied using XRD, field emission SEM (FESEM), andEDX, and ZnO grains, bismuth rich regions and spinel phases were identified. Discs made from oxide doped nano-ZnO show considerably higher breakdown voltage (656¡30 V mm21) compared to those prepared frommicrometre sized ZnO (410¡30 V mm21) and commercial varistors (454¡30 V mm21). However, varistors madefrom the nano-ZnO show very low densification and high leakage current, making them unsuitable for devicefabrication.