Giant dielectric constant response in a copper-titanate

We describe a material, cubic CaCu3Ti4O12, which exhibits a large dielectri c response, the temperature-dependence of which has not been seen, to our k nowledge, in any existing material. This compound possesses a low-frequency dielectric constant, epsilon similar to 10(4) [1], which is only weakly va rying in the temperature range 100-400 K. Below T similar to 100 K, however , there is an abrupt 100-fold reduction in the value of epsilon. X-ray diff raction and thermodynamic data argue against an explanation in terms of fer roelectricity, i.e. the collective ordering of local dipole moments. Both t he low-frequency dielectric response as well as Raman scattering data sugge st the existence of highly polarizable relaxational modes with a characteri stic gap energy of 28 meV. (C) 2000 Elsevier Science Ltd. All rights reserv ed.