Ikuo Nagasawa

Capacitance‐vs‐voltage characteristics of ZnO varistors

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 Schottky‐barrier model of the grain‐boundary region, the barrier height φ and donor concentration Nd of ZnO grains were obtained by the modified 1/C2‐V plot reduced from observed C‐V relations. φ and Nd were obtained as 0.72 V and 1.6×1018 cm−3, respectively, for a ZnO‐Pr6O11‐Co3O4 system and 1.00 V and 0.76×1018 cm−3, respectively, for a ZnO‐Pr6O11‐La2O3‐Co3O4 system. These results support the validity of this model and the treatment.

Non-Ohmic Properties of ZnO-Rare Earth Metal Oxide-Co3O4 Ceramics

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 A. 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.