Non-intrinsic origin of the Colossal Dielectric Constants in CaCu3Ti4O12
  The dielectric properties of CaCu3Ti4O12, a material showing colossal values of the dielectric constant, were investigated in 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 sample thickness, provide clear evidence that the apparently high values of the dielectric constant in CaCu3Ti4O12 are non-intrinsic 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. 
P. Lunkenheimer, R. Fichtl, S.G. Ebbinghaus, A. Loidl