Characterization of SnO2-varistors with different additives

Some aspects of the effects of additives on the sintering process and their influence on the microstructure and electrical properties of SnO2 varistors are still not well understood. Aiming at a better interpretation of the involved phenomena, the effects on microstructures and electrical properties of adding Co3O4, CuO, MnO2, Bi2O3 and Sb2O3 to SnO2 have been studied. We found that Co3O4 and MnO2 enhance the densification of these ceramics by increasing the number of oxygen vacancies and, as a consequence, the sintering rate increases. Sb2O3, on the other hand, reduces the oxygen vacancy concentration and then the sintering rate is decreased. CuO and Bi2O3 form a liquid phase during the sintering process enhancing the sintering rate. We found that electrical properties are improved by the addition of all the studied dopants, due to the modifications in the microstructure and in the defect concentration. (C) 1998 Elsevier Science Limited. All rights reserved.