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In this research, DC degradation for ZnO varistors at 3.2 kV/cm and 50 mA/cm2 for 115 hours was performed, and its effect on electrical properties and defects of ZnO varistors was investigated. It was found that the breakdown field and nonlinear coefficient drops sharply from 2845 V/cm to 51.6 V/cm and 38.3 to 1.1, respectively, when the DC degradaion time reaches 115 hours. For the degraded sample, the dielectric loss was dominated by the increase of conductivity so that some defect relaxation peaks cannot be observed is the DC degraded ZnO varistors. However, in electrical modulus plot, one relaxation peak can be observed. The conductivity in low frequency range increases greatly and the conductance activation energy drops from 0.84 to 0.083 eV. Additionally, the heat-treatment process of ZnO varistors at 800 ℃ for 24 hours was also performed. It is interesting to note that the electrical properties and the relaxation processes of ZnO varistor is restorable completely again after heat-treatment. The breakdown field and the nonlinear coefficient increase to 3085 V/cm and 50.8, respectively, and the activation energy of conductance increases to 0.88 eV. It is also found that the defect relaxation peak, which is shown in dielectric spectra corresponding to oxygen vacancy defect, is suppressed evidently by heat-retreating. Therefore, it is proposed that oxygen is likely to diffuse into the ZnO grain boundaries at the heat-treatment process, which can play an important role in restorability of the DC degraded ZnO varistor.
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Keywords:
- ZnO varistors /
- dielectric properties /
- DC degradation /
- heat-treatment
[1] Gupta T K, Straub W D 1989 J. Appl. Phys. 66 6132
[2] Xu D, Shi L Y, Wu Z H, Zhong Q D, Wu X X 2009 J. Eur. Ceram. Soc. 29 1789
[3] Zhao K Y, Zeng H R, Li G R, Song H Z, Cheng L H, Hui S X, Yin Q R 2009 Chin. Phys. Lett. 26 100701
[4] Li S T, Yang Y, Zhang L, Cheng P F, Li J Y 2009 Chin. Phys. Lett. 26 077201
[5] Zhao X T, Li J Y, Li H, Li S T 2012 Acta Phys. Sin. 61 153103 (in Chinese) [赵学童, 李建英, 李欢, 李盛涛 2012 61 153103]
[6] Wang Y P, Cheng P F 2010 Insulators and Surge Arresters 4 34 (in Chinese) [王玉平, 成鹏飞 2010 电瓷避雷器 4 34]
[7] Gupta T K 1990 J. Am. Ceram. Soc. 73 1817
[8] Li S T, Cheng P F, Wang Y P 2008 Insulators and Surge Arresters 4 16 (in Chinese) [李盛涛, 成鹏飞, 王玉平, 朱斌 2008 电瓷避雷器 4 16]
[9] Yin G L, Li J Y, Yao G, Cheng P F, Li S T 2010 Acta Phys. Sin. 59 6345 (in Chinese) [尹桂来, 李建英, 尧广, 成鹏飞, 李盛涛 2010 59 6345]
[10] Chen J D, Liu Z Y 1982 Dielectric Physics (Beijing: Mechanical Industry Press) p151 (in Chinese) [陈季丹, 刘子玉 1982 电介质物理学 (北京: 机械工业出版社) 第151页]
[11] Jonscher A K 1996 Universal Relaxation Law (London: Chelsea Dielectrics Press)
[12] Tripathi R, Kumar A, Bharti C, Sinha T P 2010 Curr. Appl. Phys. 10 676
[13] Roling B, Happe A, Funke K, Ingram M D 1997 Phys. Rev. Lett. 78 2160
[14] Yin G L, Li J Y, Li S T 2009 Acta Phys. Sin. 58 4219 (in Chinese) [尹桂来, 李建英, 李盛涛2009 58 4219]
[15] Cheng P F, Li S T, Li J Y 2009 Acta Phys. Sin. 58 5721 (in Chinese) [成鹏飞, 李盛涛, 李建英 2009 58 5721]
[16] Cheng P, Li S, Zhang L, Li J 2008 Appl. Phys. Lett. 93 012902
[17] Zhao X T, Li J Y, Li S T 2012 J. Appl. Phys. 111 124106
[18] Greuter F 1995 Solid State Ionics 75 67
[19] Li J Y, Li S T, Liu F Y, Alim M A 2006 J Mater Sci: Mater Electron 17 211
[20] Sinclair D C, West A R 1989 J. Appl. Phys. 66 3850
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[1] Gupta T K, Straub W D 1989 J. Appl. Phys. 66 6132
[2] Xu D, Shi L Y, Wu Z H, Zhong Q D, Wu X X 2009 J. Eur. Ceram. Soc. 29 1789
[3] Zhao K Y, Zeng H R, Li G R, Song H Z, Cheng L H, Hui S X, Yin Q R 2009 Chin. Phys. Lett. 26 100701
[4] Li S T, Yang Y, Zhang L, Cheng P F, Li J Y 2009 Chin. Phys. Lett. 26 077201
[5] Zhao X T, Li J Y, Li H, Li S T 2012 Acta Phys. Sin. 61 153103 (in Chinese) [赵学童, 李建英, 李欢, 李盛涛 2012 61 153103]
[6] Wang Y P, Cheng P F 2010 Insulators and Surge Arresters 4 34 (in Chinese) [王玉平, 成鹏飞 2010 电瓷避雷器 4 34]
[7] Gupta T K 1990 J. Am. Ceram. Soc. 73 1817
[8] Li S T, Cheng P F, Wang Y P 2008 Insulators and Surge Arresters 4 16 (in Chinese) [李盛涛, 成鹏飞, 王玉平, 朱斌 2008 电瓷避雷器 4 16]
[9] Yin G L, Li J Y, Yao G, Cheng P F, Li S T 2010 Acta Phys. Sin. 59 6345 (in Chinese) [尹桂来, 李建英, 尧广, 成鹏飞, 李盛涛 2010 59 6345]
[10] Chen J D, Liu Z Y 1982 Dielectric Physics (Beijing: Mechanical Industry Press) p151 (in Chinese) [陈季丹, 刘子玉 1982 电介质物理学 (北京: 机械工业出版社) 第151页]
[11] Jonscher A K 1996 Universal Relaxation Law (London: Chelsea Dielectrics Press)
[12] Tripathi R, Kumar A, Bharti C, Sinha T P 2010 Curr. Appl. Phys. 10 676
[13] Roling B, Happe A, Funke K, Ingram M D 1997 Phys. Rev. Lett. 78 2160
[14] Yin G L, Li J Y, Li S T 2009 Acta Phys. Sin. 58 4219 (in Chinese) [尹桂来, 李建英, 李盛涛2009 58 4219]
[15] Cheng P F, Li S T, Li J Y 2009 Acta Phys. Sin. 58 5721 (in Chinese) [成鹏飞, 李盛涛, 李建英 2009 58 5721]
[16] Cheng P, Li S, Zhang L, Li J 2008 Appl. Phys. Lett. 93 012902
[17] Zhao X T, Li J Y, Li S T 2012 J. Appl. Phys. 111 124106
[18] Greuter F 1995 Solid State Ionics 75 67
[19] Li J Y, Li S T, Liu F Y, Alim M A 2006 J Mater Sci: Mater Electron 17 211
[20] Sinclair D C, West A R 1989 J. Appl. Phys. 66 3850
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