ZNO VARISTORS WITH BACOO3-X (0.12-GREATER-THAN-X-GREATER-THAN-0) AS THE ONLY FORMULATING PHASE

Varistors prepared from ZnO with 1-3 mole% 2H-perovskite, BaCoO3-x (0.12 > x > 0), have nonlinearity index, is-porportional-to, upto 35. Nonlinear resistivity is observed only when the oxygen deficiency of BaCoO3-x is < 0.12, together with controlled processing parameters such as the method of mixing, sintering temperature, cooling rate and postsintering treatment. The nonlinear property originates as a result of higher concentration of Co (III) present at the more insulating grain boundary layers, being charge-compensated by zinc vacancies. Whereas, the grain interiors are conducting because of the donor states arising out of the frozen-in oxygen vacancies, as revealed by the EPR results.