Effect of annealing on electrical responses of electrode and surface layer in giant-permittivity CuO ceramic

The effect of heat treatments on the electrical responses of the electrode and surface layer in a giant-permittivity CuO ceramic is investigated. It is found that the giant low-frequency relative permittivity of the CuO ceramic can be tuned by annealing in Ar and O₂—it can be reduced by annealing in Ar, and then it can be enhanced up to the initial value by annealing in O₂. The results indicate to the effect of oxygen vacancy concentration on the giant dielectric properties of the CuO ceramic. Interestingly, three sets of dielectric relaxations are observed in the O₂–annealed sample, which can be assigned as the effects of outmost surface layer, electrode, and grain boundary. Our results reveal that the giant low-frequency dielectric response in the CuO ceramic is associated with both of the interfacial polarization at the sample–electrode interface resulted from a non-Ohmic electrode contact and the outmost surface layer-inner part interface.