Dependence of residual voltage ratio behavior of SnO-based varistors on NbOaddition

SnO2-based varistor samples doped with Co2O3,Nb2O5 and Cr2O3 were prepared by ball-mixed oxide method.The microstructure,nonlinear I-V characteristic and surge current performances of these samples were investigated.This paper mainly focused on the dependence of the residual voltage ratio behavior of SnO2-based varistors on Nb2O5 addition,different factors influencing the residual voltage ratio in different concentration of Nb2O5 were analyzed.The Nb2O5 addition influences its residual voltage ratio by changing the grain size,forming defects(especially the free electrons) and cumulative effect.The measured results indicated that the optimally obtained sample with 0.07mol% Nb2O5 possesses the lowest residual voltage ratio of 1.86,the corresponding nonlinear coefficient and the threshold electric field are 42.6 and 364.6 V/mm,respectively.