Abstract
In this study, the grain growth behaviour of ZnO-V2O5-based ceramics with 0.25–0.75 mol% additions of PrMnO3 was systematically investigated during sintering from 850 °C to 925 °C. with the aim to control the ZnO grain size for their application as varistors. It was found that with the increased addition of PrMnO3, in addition to the decrease in the average grain size, the grain size distribution also narrowed and eventually changed from a bimodal to unimodal distribution after a 0.75 mol% PrMnO3 addition. The grain growth control was achieved by a pinning effect of the secondary ZnCr2O4 and PrVO4 phases at the ZnO grain boundaries. The apparent activation energy of the ZnO grain growth in these ceramics was found to increase with increased additions of PrVO4, hence the observed reduction in the ZnO grain sizes.
Highlights
ZnO-Bi2 O3 ceramics are an established class of ZnO-based varistors
This study investigated the effect of increased additions of PrMnO3 on the grain growth of ZnO-V2 O5 ceramics, with the aim to control the average grain size and size distribution of ZnO to improve their electrical properties as practical varistors
The resulting ZVCP75 sample was shown to have a markedly improved stability in its switching field strength. This was consistent with the results reported by Hng et al [12], which showed that the presence of just a few abnormally grown ZnO grains could have a pronounced destabilisation effect on the switching field strength of ZnO-V2O5 varistors
Summary
ZnO-Bi2 O3 ceramics are an established class of ZnO-based varistors. It is well known that the nonlinear current–voltage (I–V) characteristics of these ZnO-Bi2 O3 varistors are directly dependent on their microstructures, mainly the average grain size and size distribution of ZnO [1]. ZnO-V2 O5 based ceramics suffer from a distinct disadvantage in that they have been shown to exhibit abnormal ZnO grain growth [17] This is commonly attributed to the high reactivity of the V2 O5 -rich liquid phase formed during sintering. With Sb2 O3 , the addition of up to 2 mol% is needed to control the grain growth of ZnO-V2 O5 ; the addition of Sb2 O3 increases the required sintering temperature for the system. This study investigated the effect of increased additions of PrMnO3 on the grain growth of ZnO-V2 O5 ceramics, with the aim to control the average grain size and size distribution of ZnO to improve their electrical properties as practical varistors
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