Electronic relaxation of deep bulk trap in CaCu3Ti4O12 ceramics: Post-annealing studies

The influence of annealing after sintering on the non-ohmic and dielectric behavior of CaCu₃Ti₄O₁₂ ceramics was investigated from -140 to 200 °C. Sintering at 1080 °C was followed by a cooling rate of 2.5 °C/min and quenching to ambient temperature for comparison. And both ceramic samples were annealed in flowing O₂, then N₂ and O₂ again at 950 °C. It was found that annealing in O₂ can reduce dielectric loss and enhance non-ohmic behavior of the quenched sample, while dielectric loss rose back up again after annealing in N₂. On the contrary, the slow cooled sample showed low dielectric loss, analogous to annealing in O₂. Trapped electron relaxation processes caused by V_o⁺ and V₀⁺⁺ in the depletion layer of Schottky barrier can be identified, and the energy levels were deduced to 0.10 eV and 0.49 eV respectively. A relaxation with an energy level of 0.66 eV was detected in slowly cooled sample, which can be eliminated by annealing in N₂ and then re-created by annealing in O₂. This energy level was proposed to relate with the additional interface states caused by oxygen adsorption along the interface. Introducing more electronegative defects at boundaries was supposed as a promising solution to promote the application of CCTO as non-ohmic device with low dielectric loss.