Resumo:
This study presents the results obtained for the synthesis and electric
characterization of a SnO2 ceramic varistor. High densification ceramics were
attained using a ternary system SnO2.Co2O3.Cr2O3. With the specific purpose of
incrementing the non-linearity coefficient, the system was doped with internal
transition elements: dysprosium (Dy), europium (Eu), praseodymium (Pr) and
neodymium (Nd). The doping concentration was maintained at 0.05% wt. The
ceramic microstructures were analyzed by means of scanning electron microscopy
(SEM). The morphology and crystalline phase were analyzed by X ray diffraction.
The formation of secondary phases was not observed in the ceramic phases study,
as no characteristic peaks were present other than the usual SnO2 peaks. The best
results regarding the non-linear effect were achieved by the europium doping
SnO2. The non-linearity coefficients obtained in this study were: α(Eu) = 65.96;
α(Nd) = 38.33; α(Dy) = 31.57 and α(Pr) = 17.27. The SEM analysis evidenced
that the ceramic densification was function of the metal doping, showing low
pores formation and an increase in the grain average size with respect to pure
SnO2; the electric properties of varistors were function of temperature. Also, the
rupture voltage value (Vr) was seen to be function of the average size of the grain.
