The study of trivalent donor dopants is one of the main research subjects in the varistor area. Several researchers have been studying these dopants aiming at a better understanding of the effects of their addition on the electrical and microstructural properties of these electronic ceramics. Both transition and rare earth metals have been added to SnO2-based ceramics with the purpose of assessing their behavior. It has been observed that some of these oxides, such as Cr2O3 and La2O3, improve significantly the electrical properties of the varistors, whereas other oxides, such as Bi2O3 and Er2O3, for example, do not produce such effect. Improvements in the varistor behavior have been attributed to the different oxygen species produced by the reactions with these dopants. This review shows what has been studied recently, in terms of the dopants incorporated into the SnO2-based varistor lattices.
varistors; electrical properties; microstructure
