Excellent dielectric performance and nonlinear electrical behaviors of Zr-doped CaCu₃Ti₄O₁₂ thin films

The dielectric and nonlinear current–voltage properties of CaCu₃Ti_4−xZr _x O₁₂ (x = 0, 0.05, 0.1, 0.15 and 0.2) thin films prepared by the modified sol–gel method and annealed at 750 °C for 1 h were systematically studied. Zr doping resulted in a significant reduction in the mean grain size from 177.4 to 42.9 nm. The dielectric properties of the thin films increased significantly with the increase of Zr content from x = 0 to 0.2, indicating the importance of microstructure in controlling the dielectric properties of CaCu₃Ti_4−xZr _x O₁₂ thin films. A highly frequency-independent giant dielectric permittivity from 10² to 10⁶ Hz was successfully achieved in CaCu₃Ti_3.8Zr_0.2O₁₂ thin film, which possessed a very high dielectric permittivity value of 7591 and a very low tanδ value of 0.023 at 1 kHz. The results indicated that reduction in the mean grain size affected the number of polarized ions per unit volume n₀ (to improve ε′) and the number of grain boundaries (to reduce tanδ). CaCu₃Ti_3.75Zr_0.15O₁₂ thin film showed the highest nonlinear coefficient (5.8) and lowest leakage current (131 μA). In addition, the relaxation mechanism based on the internal barrier layer capacitance model and the back-to-back dual Schottky barrier model were used to explain the dielectric properties and the nonlinear electrical behaviors of the samples.