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.

Keywords

varistor ceramics / zinc oxide / Yb₂O₃ / microstructure / electrical properties

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