Compositional changes adjacent to grain boundaries during electrical degradation of a ZnO varistor

Abstract
Compositional changes adjacent to grain boundaries in heavily degraded samples of a ZnO varistor containing the additives Bi and Co have been observed with the scanning transmission electron microscope. A marked asymmetry in the distribution of Bi and Co with respect to the physical location of the boundary is found, consistent with the accumulation of mobile cations on one side of the boundary under the influence of a dc electric field.

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