Abstract
Pelletized samples of polycrystalline zinc oxide ceramics doped with 2mol% MnO 2 and 3mol% PbO were prepared by the conventional method of ceramic processing. The requisite composition was obtained by the direct mixing of constituent phases (DMCP) technique. Sintering was carried out at various temperatures ranging from 650 o C to 850 o C. The effects of sintering on the non-linear characteristics of the doped ceramic samples were investigated. The threshold or breakdown voltages were found to decrease as sintering temperature increased. Microstructural investigation revealed improved homogeneity and increased grain sizes with increasing sintering temperature. The random distribution of secondary phases also featured prominently. These findings were observed to correlate with the evolution of electrical characteristics while the sample sintered at 850 o C exhibited the best electrical response suitable for varistor behaviour.
Highlights
A number of studies have successfully proved that n- type doped zinc oxide ceramics are effective material for varistors or voltage- dependent resistors (VDR), using transition metal oxides as the dopant
In our previous investigations (Akinnifesi et al, 2014) we studied the electrical properties of Mn2+- Pb2+- doped ZnO varistors and found this to be considerably influenced by the microstructure
Densification at higher sintering temperatures can be improved by increasing the Mn doping level as this has been found to promote grain growth in the final stages of sintering (Han et al, 2002)
Summary
A number of studies have successfully proved that n- type doped zinc oxide ceramics are effective material for varistors or voltage- dependent resistors (VDR), using transition metal oxides as the dopant. Varistors have applications in the protection of electrical power transmission and electronic circuit devices against transient voltage surges (Gupta, 1990; Leach, 2005; Annas et al, 2007). Their current-voltage characteristics exhibit very high resistance at low voltages and low resistance at high voltages. There have been reports in the literature on the basic physics of doped varistors (Levison et al, 1975; Entage, 1977), in addition to which a brief review will be pertinent here
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