[3] [3] CHEN G H, LI J L, YUAN C L, et al. Effect of Sm2O3 dopant on microstructure and electrical properties of ZnO-based varistor ceramics［J］. J Mater Sci: Mater Electron, 2013, 24: 3675-3679.

[4] [4] CHEN G H, LI J L, YANG Y, et al. Microsturcture and electrical properties of Dy2O3 doped ZnO-Bi2O3 based varistor ceramics［J］. Materials Research Bulletin, 2014, 50:141-147.

[5] [5] LI J L, CHEN G H, YUAN C L. Microstructure and electrical properties of rare earth doped ZnO-based varistor ceramics［J］. Ceramics International, 2013, 39(3):2231-2237.

[6] [6] CAO Z C, ZHENG L Y, CHENG L H, et al. Influence of CeO2-doping on the electrical properties of ZnO-Bi2O3-based varistor ceramics［J］. Key Engineering Materials, 2016, 697:262-266.

[7] [7] XU D, WU J T, JIAO L. Highly nonlinear property and threshold voltage of Sc2O3 doped ZnO-Bi2O3 -based varistor ceramics［J］. Journal of Rare Earths, 2013, 31(2):158-163.

[8] [8] YANG C, ZHU D C, ZENG T, et al. Microstructure and electrical properties of La2O3 and Sm2O3 co-doped ZnO-based varistor ceramics prepared from nanosize ZnO powder［J］. Journal of Electronic Materials, 2015, 44(8):2651-2656.

[9] [9] BAI H R, LI S H, ZHAO Y H, et al. Influence of Cr2O3 on highly nonlinear properties and low leakage current of ZnO-Bi2O3 varistor ceramics［J］. Ceramics International, 2016 42:10547-10550.

[11] [11] XU D, CHENG X N, WANG M S, et al. Microstructure and electrical properties of La2O3-doped ZnO-Bi2O3 based varistor ceramics［J］. Advanced Materials Research, 2009, 77/182: 2007-2010.

[12] [12] ANTOINE I, SOPHIE G F, CLAUDE E, et al. Microstructure control to reduce leakage current of medium and high voltage ceramics varistors based on doped ZnO［J］. Journal of the European Ceramic Society, 2014, 34: 3707-3714.