Comparative characteristics of yttrium oxide and yttrium nitric acid doping in ZnO varistor ceramics

Abstract

The effect of different molar ratios of Y₂O₃ and Y(NO₃)₃ on the microstructure and electrical response of ZnO-Bi₂O₃-based varistor ceramics sintered at 1 000 °C was investigated, and the mechanism by which this doping improves the electrical characteristics of ZnO-Bi₂O₃-based varistor ceramics was discussed. With increasing amounts of Y(NO₃)₃ or Y₂O₃ in the starting composition, Y₂O₃, Sb₂O₄ and Y-containing Bi-rich phase form, and the average grain size significantly decreases. The average grain size significantly decreases as the contents of rare earth compounds of Y(NO₃)₃ or Y₂O₃ increase. The maximum value of the nonlinear coefficient is found at 0.16% Y(NO₃)₃ or 0.02% Y₂O₃ (molar fraction) doped varistor ceramics, and there is an increase of 122% or 35% compared with the varistor ceramics without Y(NO₃)₃ or Y₂O₃. The threshold voltage V_T of Y(NO₃)₃ and Y₂O₃ reaches at 1 460 V/mm and 1 035 V/mm, respectively. The results also show that varistor sample doped with Y(NO₃)₃ has a remarkably more homogeneous and denser microstructure in comparison to the sample doped with Y₂O₃.

Keywords

ceramics / varistor / rare earth / microstructure / electrical properties

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