Al-doped ZnO varistors prepared by a two-step doping process

ABSTRACT

It is difficult to dope Al into main grains of ZnO varistor ceramics, especially for small doping amount. Generally, all raw materials including Al dopant are directly mixed together and sintered into ceramics. However, in this direct doping process, Al is apt to stay in grain boundaries, and almost does not enter grains. This does harm to the electrical properties of ZnO varistors. In this paper, we proposed a two-step doping process. Al₂O₃ powder was first mixed only with a part of the ZnO powder and pre-sintered. The pre-sintered powder was mixed with other additives such as Bi₂O₃ and the rest ZnO. Then ZnO varistor ceramics were prepared via solid state sintering processes. Results showed that two-step doped ZnO varistors exhibited improved electrical properties with a significant increased nonlinear coefficient and a great decreased leakage current compared to directly doped ones because more Al was incorporated into ZnO grains.

KEYWORDS:

• ZnO varistors
• two-step doping process
• Al₂O₃ doping

Acknowledgement

The authors thank the Analytical and Testing Center, Huazhong University of Science and Technology for the XRD and SEM measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Qiuyun Fu http://orcid.org/0000-0001-6352-5144

Chunfeng Ke http://orcid.org/0000-0002-7767-4893

Zhiping Zheng http://orcid.org/0000-0002-9613-2117

Additional information

Funding

This work was supported by The National Key Research and Development Program of China [grant number 2017YFB0406301].