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ceramic materials
zinc-oxide-based varistor materials

Owing to their exceptional non-linear current-voltage characteristics and energy absorption capability, varistors based on zinc oxide (ZnO) ceramics doped with small amounts of Bi2O3, Sb2O3, Mn3O4, Co3O4, Cr2O3, NiO, and others, are extensively used for over-voltage protection. The performance of a varistor ceramic is closely related to its microstructure.

Our investigations are directed toward a comprehensive understanding of the correlations between the microstructure and the electrical characteristics of varistor ceramics in order to be able to tailor their performance in accordance with needs and demands.

These investigations include understanding the processes of microstructure development and in particular ZnO grain growth, the role of standard dopants and possible new dopants like selected rare-earth oxides in these processes and their influence on the non-linearity of the grain boundaries and the conductivity of the ZnO grains.

 

Through the optimization of the starting composition using a range of dopants and the adjustment of the ratios among them a threshold voltage (V/mm) from a few tenths of volts up to a several hundred volts at the required non-linear and energy characteristics can be achieved. In the previous year the results of these studies were used for the enhancement of the low-voltage varistors, the miniaturization of medium-voltage energy varistors by a reduction of their thickness, and the development of miniaturized high-voltage varistor blocks as elements for surge arresters.


Phase composition of a ZnO-based varistor ceramics; Z: ZnO
phase, B: Bi
2O3-rich phase, S: Zn7Sb2O12 spinel-type phase,
PY: Bi
3Zn2Sb3O14 pyrochlore-type phase, P:pore

 

comments & suggestions to:  sanja fidler