Charge transfer in the high dielectric constant materials CaCu3Ti4O12 and CdCu3Ti4O12

The cubic perovskite-related ceramic CaCu 3 Ti 4 O 1 2 has a very high static dielectric constant e 0 ≥10 000 at room temperature (RT), which drops to about 100 below ≃ 100 K. Substituting Cd for Ca reduces the RT value of e 0 by over an order of magnitude. The origin of the large e 0 is not fully understood, but may be due to an internal barrier layer capacitance (IBLC) effect. Infrared measurements on the Ca and Cd compounds show that low-frequency modes increase dramatically in strength at low temperature, suggesting a change in the effective charges and increasing electronic localization that may lead to a breakdown of the IBLC effect.