The electrical properties of ZnO varistors are induced by a sintering step. The phenomena occurring during this thermal treatment
have been studied through model systems whose nature and composition are well defined. The pure BiSbO4 and Bi3 Zn2 Sb3 O14 phases have been synthetised by Direct Oxidation of a Precursory Alloy (DOPA) and characterized using XRD method. Each one
of these phases can react with zinc monoxide through an invariant isobaric reaction in the ZnO–Bi2 O3 –Sb2 O3 system:
– at 998C 17/3<ZnO>+2/3<Bi3 Zn2 Sb3 O14 > arrow <Zn7 Sb2 O12 > + ((Bi2 O3 ))
– at 1058C 7<ZnO>+2<BiSbO4 > arrow <Zn7 Sb2 O12 >+((Bi2 O3 ))
These thermodynamic considerations can explain the thermal domain of the sintering reaction described in the literature.