GRAIN-BOUNDARY SEGREGATION IN A COMMERCIAL ZNO-BASED VARISTOR

By using thin-film x-ray spectroscopy, it is found that the grain boundaries of a commercially available ZnO-based varistor which are devoid of a discrete intergranular phase are nevertheless enriched in bismuth. No direct measurement of the bismuth concentration could be made but an estimate is obtained by comparing the observed intensity of the bismuth peaks from the grain boundary to that from a bismuth containing thin intergranular film of measurable thickness. In this manner, it is estimated that bismuth is concentrated to within about 20 Å of either side of the grain boundary, a value commensurate with that obtained previously by Auger electron spectroscopy.