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1 Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

1 2004

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Peculiarities of ZnO-based varistor ceramics doped with Ba-Bi compounds

Mielcarek W., Bernik S., Prociów K.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

2004

Vol. 40, nr 15

158-161

Varistor ceramics added with Ba-Bi and Ti is distinguished by enhanced mechanical and electrical features in comparison to the typical multicomponent ZnO ceramics. In the case of typical varistor ceramics during heating to sintering temperature forms the Bi-Sb-Zn pyrochlore phase which reacts with ZnO delivering Bi2O3 fraction in much volume. Bi2O3 volume fraction containing Bi2O3 crystallites and other secondary (spinels, pyrochlore) phases are of no importance to ZnO wet-ability or varistor a value. Just opposite, it develop tensile stresses and electrically useless areas in varistor body. The following research was intended to find the way of restricting the volume of an intergranular phase in varistor body. It was found out that when varistor ceramics is added with Bi-Ba compound, the pyrochlore phase cannot form so easy and in so much quantity, as the Ba-Bi decomposition to Bi2O3 occurs only in presence of some Ba reactant. In this case it was Ti which, as each of varistor additive, was well dispersed and present in varistor body in small quantity. What more in the case of Ba-Bi added ceramics the amount of other additives, which in typical technology are added in access, can be restricted.; As it appeared from SEM images of varistors microstructure it benefited the varistor body in better homogeneity of Bi2O3 rich intergranular phase and less quantity of secondary phases. The lower amount of secondary phases at the grain boundaries contributed to increase of effective contacts between ZnO grains In the effect also varistor electrical properties improved considerably.