Optical response of high-dielectric-constant perovskite-related oxide

Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is similar to 80 at room temperature, which is far smatter than the value of similar to 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very tow frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or similar to 500 nanoseconds) but increase dramatically at tow temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical stowing down of dipolar fluctuations in nanosize domains.