Studies were made on the capacitance-vs-voltage characteristics of ZnO varistors which contain rare-earth metal oxides and cobalt oxide. On the basis of the symmetrical

Zinc oxide ceramics containing rare earth metal oxide and cobalt oxide which exhibit non-ohmic current-voltage characteristics were studied. The nonlinearity was similar to that of the zinc oxide varistor containing Bi2O3 and other additives. According to microstructural observations, the intergranular layer of the ceramics was found to be a rare earth metal oxide compound without Zn and Co atoms, and its thickness was expected to be less than 100 Å. The nonlinear characteristics are attributed to the potential barrier due to the depletion layer formed in the interfacial region of the ZnO grainboundaries doped with Co atoms. Qualitative analysis of capacitance-voltage relations confirmed this model.

No abstract

Zinc oxide elements have been developed, which contain praseodymium oxide rather than bismuth oxide as a principal additive component. These elements have been used to produce gapless surge arresters with rated voltages up to 360kV. The 2-phase microstructure of these elements increases the active area of grain boundaries which is the origin of non-linearity in V-I relation.Consequently the effective area of the electrodes is increased resulting in a higher apparent dielectric constant of the element by a factor of 1.5 and higher capability for short wave front discharge withstand. The absorption capability for long duration discharge was improved by obtaining higher resistance at the peripheral of the element than at the inner area.

No abstract