SCANNING AUGER MICROPROBE INVESTIGATION OF GRAIN BOUNDARY SEGREGATION IN SOME ELECTROCERAMICS

Spatial distributions of elements near the grain boundaries of both ZnO varistors and NiO ceramics were investigated by a scanning Auger microprobe. In ZnO varistors doped with Bi and Co, the content of the additive Bi segregated at every grain boundaries measured in the range from 2 to 10 nm in thickness. In many segregation layers, a total molar fraction of cations, Zn and Bi, was higher than that of oxygen, suggesting that the segregated Bi was in a state with a deficit of oxygen. In NiO ceramics doped with Li, the content of the additive Li segregated at grain boundaries in the range from 10 to 20 nm in thickness. In this material, contrary to the cases of the varistor, the segregated Li was in a state with a surplus of oxygen