Charge transfer in the high dielectric constant materials CaCu3Ti4O12 and CdCu3Ti4O12

Abstract

The cubic perovskite-related ceramic ${\mathrm{CaCu}}_3{\mathrm{Ti}}_4{\mathrm{O}}_{12}$ has a very high static dielectric constant ${\varepsilon }_0\gtrsim 10000$ at room temperature (RT), which drops to about 100 below $\simeq 100\mathrm{K}.$ Substituting Cd for Ca reduces the RT value of ${\varepsilon }_0$ by over an order of magnitude. The origin of the large ${\varepsilon }_0$ 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.