(A) study on the microstructure and electrical properties of the $ZnO-Bi_2O_3$ varistor dopped with $MnO-2$

Abstract

In order to investigate the $MnO_2$ dopping effect, the $ZnO-Bi_2O_3$ binary system chosen, and then the $MnO_2$ was added in the range of 0 mol% to 1 mol%. Also, in the case of ternary system dopped with the 0.5 mol% $MnO_2$, the changing effect of the sintering temperature was studied from 1000℃ to 1350℃. In this $ZnO-Bi_2O_3-MnO_2$ ternary system, the intergranular materials were detected and the segregation of $Bi_2 O_3$ was observed, but the Mn was spreaded within the ZnO grain and intergranular materials. In the V-I characteristics, the dopping of $MnO_2$ additive resulted in the increase of $V_{1mA}$/mm, but in the case of leakage current region, the decrease of leakage current was observed from 0 mol% to 0.1 mol% $MnO_2$ addition and above 0.1 mol%, the leakage current was increased again. Also, the increase of sintering temperature resulted in the decrease of the leakage current up to 1150℃, but above 1150℃, resulted in the increase of leakage current. Nonlinear coefficient was increased by increasing the $MnO_2$ content, but in 0.5 mol% $MnO_2$ dopping ternary system, was maximum at 1150℃ sintering temperature and above 1150℃, the abrupt decrease was observed. Also, the addition of more than 0.5 mol% $MnO_2$ in the studied $ZnO-Bi_2O_3$ binary system resulted in the abrupt increase of current instability.