Abstract
ZnO nanoparticles were prepared by a solid state pyrolysis reaction of zinc acetate dihydrate and oxalic acid dihydrate at 500°C. The course of reaction at various temperatures was followed by XRD. Subsequently varistors were fabricated from this nano-ZnO material by solid state mixing with various oxide additives and sintering to 1050°C. The microstructure of the sintered material was studied using XRD, field emission SEM (FESEM), and EDX, and ZnO grains, bismuth rich regions and spinel phases were identified. Discs made from oxide doped nanoZnO show considerably higher breakdown voltage (656 ± 30 V mm-1) compared to those prepared from micrometre sized ZnO (410 ± 30 V mm-1) and commercial varistors (454 ± 30 V mm-1). However, varistors made from the nano-ZnO show very low densification and high leakage current, making them unsuitable for device fabrication.
Highlights
ZnO varistors are well known electroceramic devices, which have voltage dependent switching capabilities.[1,2,3,4] Varistors are usually connected across the power line in parallel with the instrument to be protected from overvoltage surges.[3]
It should be noted that careful control of the microstructure is required to produce varistors with a high breakdown voltage as Vc is proportional to the number of active grain boundaries in the sintered body.[1,3,6,7]
Using thermogravimetric analysis (TGA) Shen et al.[14] proposed that in this reaction the ZnO is formed via zinc oxalate hydrate
Summary
ZnO varistors are well known electroceramic devices, which have voltage dependent switching capabilities.[1,2,3,4] Varistors are usually connected across the power line in parallel with the instrument to be protected from overvoltage surges.[3]. Nano-ZnO has been successfully prepared by solid state pyrolysis[14,15] and used for making a gas sensor[14] and UV emitter.[15] In this paper nano-ZnO has been prepared by the previously reported solid state pyrolysis procedure[14] and varistors have been fabricated by incorporating various additives, and sintering at 1050uC. These samples are compared to others prepared from micrometre sized ZnO
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