Improved dielectric and nonlinear properties of CaCu3Ti4O12 ceramics with Cu-rich phase at grain boundary layers

The formation and compositions of grain boundary layers are very important factors to improve the electrical properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics. In present work, the dielectric and nonlinear properties of the CCTO ceramics are enhanced by controlling the Cu-rich phase degree at grain boundary layers. The dense CCTO ceramics were prepared successfully through mixing the nanometer and micrometer powders and using the cold isostatic pressing process. The average grain size of these CCTO ceramics is about 30.71(±11.76) ～ 62.01(±32.16) μm, and their grain microstructures show the Cu-rich phases at grain boundary layers. The CCTO ceramics with the mass ratios of nanometer and micrometer powders 7:3 display a giant dielectric constant of 5.4 × 10⁴, low dielectric loss of 0.048 at 10³ Hz, enhanced nonlinear coefficients of 11.12, as well as the noteworthy breakdown field of 4466.17 V/cm. The complex impedance spectroscopy results indicate that the giant dielectric behavior is due to the electrically heterogeneous grain/grain boundary characteristics from internal barrier layer capacitance (IBLC) model. The lower dielectric loss and the higher breakdown field are attributed to the high resistance grain boundary layers with the Cu-rich phase. The improved nonlinear properties are related to the increased Schottky barrier height at grain boundary. This work may provide a potential way to design the CCTO ceramics with excellent electrical properties from the viewpoint of controlling the response of the Cu-rich phase grain boundary.