Enhanced electrical properties of CaCu₃Ti₄O₁₂ ceramics by spark plasma sintering: Role of Zn and Al co-doping

Highly dense CaCu₃Ti₄O₁₂ (CCTO) ceramics co-doped by ZnO and Al₂O₃ were synthesized by spark plasma sintering (SPS) at 750 °C for 10 min, and then annealed at 1000 °C for 3 h. The homogeneous microstructures were achieved, and the grain size was suppressed to around 2 μm. Dramatically enhanced electrical properties of CCTO ceramics were obtained when 1 mol% ZnO and Al₂O₃ were co-doped. The breakdown field was improved to 12.13 kV/cm and the nonlinear coefficient was increased to 6.59, accompanying with a low dielectric loss of 0.02 at around 1 kHz, which were ascribed to the elevation of Schottky barrier height from 0.54 eV to 0.80 eV. Comparing with the pure CCTO sample, the activation energy of grain boundary obtained from the impedance spectra increases from 0.64 eV to 0.92 eV. Additionally, the grain and grain boundary resistance were also discussed based on the Cole-Cole plot, from which the grain boundary resistance was found to be increased significantly from 3.8 × 10⁵ Ω to 4.0 × 10⁶ Ω after co-doping.