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.

Graphical abstractThis figure shows the frequency dependence of ɛ′ for the samples of CuO–as, CuO–Ar, and CuO–O2 at 293 K. It is seen from the figure that the dielectric constant is decreased by one order of magnitude after the as prered sample (CuO–as sample) was annealed in Ar atmosphere (CuO–Ar sample). Interestingly, the value of ɛ′ can be increased to the initial value by annealing the CuO–Ar sample in O2 atmosphere (CuO–O2 sample). These results strongly indicate that the oxygen vacancy has a great influence on the dielectric properties of the CuO ceramic.Figure optionsDownload full-size imageDownload as PowerPoint slide