High Performance ZnO Varistors Prepared From Nanocrystalline Precursors for Miniaturised Electronic Devices
High Performance ZnO Varistors Prepared from Nanocrystalline Precursors for Miniaturised Electronic Devices, Suresh C. Pillai,* John M. Kelly, Declan E. McCormack, Ramesh Raghavendra, J. Mater. Chem, 18, 2008, 3926–3932
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.