Nonintrinsic origin of the colossal dielectric constants in CaCu₃Ti₄O₁₂

The dielectric properties of CaCu₃Ti₄O₁₂, a material showing colossal values of the dielectric constant, were investigated over a broad temperature and frequency range extending up to 1.3 GHz. A detailed equivalent-circuit analysis of the results and two crucial experiments, employing different types of contacts and varying the sample thickness were performed. The results provide clear evidence that the apparently high values of the dielectric constant in CaCu₃Ti₄O₁₂ are nonintrinsic and due to electrode polarization effects. The intrinsic properties of CaCu₃Ti₄O₁₂ are characterized by charge transport via hopping of localized charge carriers and a relatively high dielectric constant of the order of 100.