Optical Response of High-Dielectric-Constant Perovskite-Related Oxide

TLDR

Optical conductivity measurements on CaCu₃Ti₄O₁₂ suggest that its giant dielectric effect originates from charge redistribution within the unit cell. The material exhibits a low‑frequency vibrational anomaly and a dielectric constant of ~80 at terahertz versus ~10⁵ at kilohertz, indicating strong low‑frequency dipole relaxation with relaxation times of ~500 ns at room temperature that lengthen dramatically at low temperature, consistent with relaxor‑like slowing of nanoscale dipolar fluctuations.

Abstract

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 approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.