High Dielectric Constant and Dielectric Relaxations in La_2/3Cu₃Ti₄O₁₂ Ceramics

La_2/3Cu₃Ti₄O₁₂ ceramics were prepared by the same method of solid-state reaction as CaCu₃Ti₄O₁₂ ceramics. The structure and dielectric responses for La_2/3Cu₃Ti₄O₁₂ and CaCu₃Ti₄O₁₂ ceramics were systematically investigated by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, and impedance analyzer. Compared with CaCu₃Ti₄O₁₂ ceramics, La_2/3Cu₃Ti₄O₁₂ ceramics with higher density and refined grain exhibit a high dielectric constant (ε' ~ 10⁴) and two dielectric relaxations in a wide temperature range. The dielectric relaxation below 200 K with an activation energy of 0.087 eV in La_2/3Cu₃Ti₄O₁₂ ceramics is due to the polyvalent state of Ti³⁺/Ti⁴⁺ and Cu⁺/Cu²⁺, while the dielectric relaxation above 450 K with higher activation energy (0.596 eV) is due to grain boundary effects. These thermal activated dielectric relaxations with lower activation energy in La_2/3Cu₃Ti₄O₁₂ ceramics both move to lower temperatures, which can be associated with the enhanced polyvalent structure in La_2/3Cu₃Ti₄O₁₂ ceramics. Such high dielectric constant ceramics are also expected to be applied in capacitors and memory devices.