Quasi-ideal Nonlinear Electrical Behavior of Polycrystalline SnO2 Ceramic Varistors Doped with SiO2

The influence of SiO2 doping on the microstructure and electrical behavior of SnO2 varistors has been studied. The varistor effect was studied over a wide range from 10(A cent E dagger'9) A to 10(4) A. It is shown that the J(E) characteristic of SnO2 ceramics exhibits a nonlinear coefficient > 100. The SiO2 doping also resulted in a sharp-abrupt upturn region in the IA cent a,not signaEuroeV characteristic, indicating a single semiconductor junction behavior. The leakage current of the varistors is rather low, on the order of 10(A cent E dagger aEuro (TM) 10) S m(A cent E dagger aEuro (TM) 1). In the upturn region of operation where the curve departs from the nonlinear relation and approaches the value of the bulk resistivity of the material, the ceramic is characterized by a current density almost independent of the applied voltage. A very small amount of SiO2 causes large perturbations of the conventional thermionic emission observed in varistor ceramic materials.