Sodium impurities in ZnO–Bi2O3–Sb2O3 based varistors

Sodium impurities are frequently present in the raw oxides that constitute the complex formulation of ZnO–Bi2O3–Sb2O3 based varistors. But actually little is known about their effect on the microstructure and the electrical response of these materials. This is the main goal of the present contribution and according to the obtained results an excessive presence of this alkaline impurity can lead to a compositional change in the Bi-rich skeleton of the varistor microstructure. As a consequence the grain growth kinetics, the densification rate and the characteristic non-linear I–V response of these electroceramics are seriously affected.