Writers: Mario Cilense, Miguel A. Ramirez, Cesar R. Foschini, Daniela R. Leite, Alexandre Z. Simões, Welson Bassi, Elson Longo, José A. Varela
Keywords: microstructure; Varistors
Abstract: The eﬀect of seed addition on the microstructure and non-ohmic properties of the SnO2+ 1%CoO + 0.05%Nb2O5ceramic-based system was analyzed. Two classes of seeds wereprepared: 99% SnO2+ 1%CuO and 99% SnO2+ 1%CoO(mol%); both classes were added to the ceramic-based systemin the amount of 1%, 5%, and 10%. The two systems contain-ing 1% of seeds resulted in a larger grain size and a lowerbreakdown voltage. The addition of 1% copper seeds producesa breakdown voltage (Vb)of~ 37 V and a leakage current (fic)of 29 lA. On the other hand, the addition of 1% cobalt seedsproduced a breakdown voltage of 57 V and a leakage currentof 70 lA. Both systems are of great technological interest forlow voltage varistor applications, by means of appropriatestrategies to reduce the leakage current. Using larger amountsof seeds was not eﬀective since the values of breakdown voltagein both cases are close to a system without seeds. To ourknowledge, there are no reports in the literature regarding theuse of seeds in the SnO2system for low voltage applications.A potential barrier model which illustrates the formation ofoxygen species (O′2(ads),O′ads, and O″ads) at the expense ofclusters near the interface between grains is proposed.