Abstract
An industrially viable solution-based processing route using minimal amounts of solvent has been used to prepare bulk quantity nanopowders (average particle size 15 ± 3 nm) for the fabrication of ZnO varistors. The xerogels, calcined powders and sintered materials were fully characterised. The preparation of varistors from nanopowders has been optimised by studying the effect of temperature on grain growth, densification and breakdown voltage. The varistors are prepared by sintering at 1050 °C for 2 hours, a temperature that is significantly lower than that used in the current industrial process. Highly dense varistor discs prepared from the sintered material produce devices, with a breakdown voltage 85% higher than that of commercial varistors, making them suitable for use in miniaturised electronic circuitry. Improved performance of these materials has been attributed to the small grain size and better dispersion of additives on ZnO grains.
Highlights
Varistors are ceramic-based semiconductors that are used in many areas of electronics and communication technology.[1,2,3,4,5,6,7] The function of a varistor is to sense and limit over-voltage surges and to function continuously without loss of performance.[1]
We have recently found that nano-ZnO synthesised from zinc acetate dihydrate and oxalic acid dihydrate either by a solution route[18] or by a solid-state pyrolysis route[19] can be used to produce varistors with an improved breakdown voltage
The xerogel dried at 80 C was calcined to 500 C for 2 hours and the powder obtained was analysed by X-ray powder diffraction (XRD) which showed the presence of only ZnO (Fig. S2, see Electronic supplementary information (ESI)†)
Summary
Varistors are ceramic-based semiconductors that are used in many areas of electronics and communication technology.[1,2,3,4,5,6,7] The function of a varistor is to sense and limit over-voltage surges and to function continuously without loss of performance.[1]. Several attempts using chemical methods have been reported for the production of varistor materials.[3,5,6,8,9,10,11,12,13,14,15,16,17,18,19] We have recently found that nano-ZnO synthesised from zinc acetate dihydrate and oxalic acid dihydrate either by a solution route[18] or by a solid-state pyrolysis route[19] can be used to produce varistors with an improved breakdown voltage.
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