Invariant reactions inducing densification of ZnO varistors

The electrical properties of ZnO varistors are induced by a sintering step. The phenomena occurring during this thermal treatment have been studied th rough model systems whose nature and composition are well defined. The pure BiSbO4 and Bi3Zn2Sb3O14 phases have been synthetised by Direct Oxidation o f a Precursory Alloy (DOPA) and characterized using XRD method. Each one of these phases can react with zinc monoxide through an invariant isobaric re action in the ZnO-Bi2O3-Sb2O3 system: - at 998 degrees C 17/3 < ZnO>+2/3 < Bi3Zn2Sb3O14> <-> <Zn7Sb2O12> + ((Bi2O 3)) - at 1058 degrees C 7 < ZnO>+2 < BiSbO4> <-> < Zn7Sb2O12>+((Bi2O3)) These thermodynamic considerations can explain the thermal domain of the si ntering reaction described in the literature.