Microstructure and electric properties of a SnO 2 based varistor

Abstract High non-linear J Â E electrical characteristic (a=41) were obtained in the Nb 2 O 5 and Cr 2 O 3 doped CoO highly densi®ed SnO 2 ceramics. X-ray diraction analysis showed that these ceramics are apparently single phase. Electrical properties and microstructure are highly dependent on the Cr 2 O 3 concentration and on the sintering temperature. Excess of Cr 2 O 3 leads to porous ceramics destroying the material's electrical characteristics probably due to precipitation of second phase of CoCr 2 O 4 . Dopant segregation and/or solid solution formation at the grain boundaries can be responsible for the formation of the electrical barriers which originate the varistor behaviour.