Influence of Yb2O3 doping on microstructural and electrical properties of ZnO-Bi2O3-based varistor ceramics

Abstract

ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% (molar fraction) were obtained by a solid reaction route. The X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were applied to characterize the phases and microstructure of the varistor ceramics, and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V–I characteristics. The XRD analysis of the samples shows that the ZnO phase, Bi2O3 phase, Zn7Sb2O12-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present, and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3. The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content. The result also shows that the threshold voltage is between 656 V/mm and 1 232 V/mm, the nonlinear coefficient is in the range of 14.1–22.3, and the leakage current is between 0.60 μA and 19.6 μA. The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 °C have the best electrical characteristics.