Degradation behavior of Ca-doped barium titanate ceramic capacitors

Electrical degradation of calcium-containing MLCCs having nickel internal electrode was studied using a highly accelerated life test set-up. Both extrinsic and intrinsic failures were identified in commercial MLCCs. From the estimated values of degradation parameters such as voltage exponent factor and pseudo-activation energy, it was found that the intrinsic failure took place by thermal runaway. Although, the degradation pattern for nickel electrode MLCCs was similar to that for common palladium electrode MLCCs, the maximum rated lifetime of the former was in the range of 5 to 30 years and was, in general, shorter than that of the latter. This difference was ascribed to the difference in oxygen vacancy concentrations. Thus, possible degradation mechanisms should be related to oxygen vacancy movement. Among them are reduction model, grain boundary barrier model and de-mixing model.