Grain Growth Control of ZnO-V2O5-Cr2O3 Based Varistors by PrMnO3 Addition

In this work, the grain growth behaviour of ZnO+V 2 O 5 (1 mol%)+Cr 2 O 3 (0.35 mol%)-based ceramics with 0.25–0.75 mol% additions of PrMnO 3 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 PrMnO 3 , not only did the average grain size decrease, but the grain size distribution also narrowed and eventually changed from a bimodal to unimodal distribution after a 0.75 mol% PrMnO 3 addition. The grain growth control was achieved by a pinning effect of the secondary ZnCr 2 O 4 and PrVO 4 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 PrVO 4 ; hence, the observed reduction in the ZnO grain sizes.