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21. Electrical performance of ZnO varistor ceramics with cobalt doped.

Author

ZHOU Libin, CHEN Hongiin, CAO Wenbin, and LIU Jianke

Abstract

Cobalt (Co) as an additive has a remarkable impact on the microstructure and electrical properties of zinc oxide (ZnO) varistor ceramics. In this paper, ZnO varistor ceramics were prepared by the conventional solid-phase method, based on the base formula of ZnO-Bi2O3-Sb2O3-MnO2-Cr2O3 with Co2O3 doped and Co3O4 doped respectively, and their microstructure and electrical properties were compared. It's found that doped Co mainly affects the average grain size of ZnO varistor ceramics, and the average grain size of samples doped Co2O3 s greater than that of samples doped Co3O4. In addition, the Co3O4 doped samples has a higher nonlinear of 51. 40, a higher breakdown field of 338. 29 V/mm, a lower leakage current density of 1.33 µA/cmµ, and a higher barrier height of 0.69 eV, which has excellent comprehensive performance. Therefore, Co3O4 s better than Co2O3 to improve microstructure and electrical properties of ZnO varistor ceramic. [ABSTRACT FROM AUTHOR]

Published
2023
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48. Influences of sintering process on (BiO-VO-MnO-YO-CoO-CrO)-doped ZnO varistors.

Author

Liu, Jianke, Chen, Yongjia, Cui, Yonghong, Han, Chen, Zhang, Cheng, Fan, Yahong, and Liang, Chuxuan

Subjects
ZINC oxide, DIELECTRIC properties, MICROSTRUCTURE, ELECTRIC fields, DIELECTRIC loss, SINTERING, VARISTORS
Abstract

The effects of sintering temperatures on the microstructure, electrical and dielectric properties of (VO-BiO-MnO-YO-CrO-CoO)-doped ZnO varistors had been researched systematically. The results showed that, when the sintering temperature increased from 870 to 930 °C, the following changes occurred: the average grain size enlarged from 0.83 to 1.67 μm and the density increased from 4.97 to 5.3 g/cm. The conclusion can be drawn that the optimal microstructure and uniformity could be obtained at 910 °C; Meanwhile, it was observed that the breakdown electrical field E decreased from 5127.3 to 2687.5 V/cm and the nonlinear coefficient α was likely to increase as the sintering temperature increased, however, the latter decreased to 15.6 sharply at 930 °C; Simultaneously, it was noted that the relative dielectric constant ε and the dielectric loss tan δ increased first and then decreased as the sintering temperature increasing when the frequency was 10 kHz. Another conclusion can be drawn that the best electrical and dielectric properties were obtained at 910 °C, where α was 27, E was 3456.5 V/cm; when the frequency was 10 kHz the values of ε and tan δ were 194 and 0.29 at this sintering temperature, respectively. Meanwhile, the temperature coefficient of resistance α was only −0.67 % and the impedance was also fairly stable at this sintering temperature. [ABSTRACT FROM AUTHOR]

Published
2017
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