Effects of powder synthesis method on dielectric properties of CaCu₃Ti₄O₁₂ ceramics

To investigate the effects of powder synthesis methods on dielectric relaxation mechanism and defect structure of CaCu₃Ti₄O₁₂(CCTO) ceramics, two kinds of CCTO ceramics were synthesized. CCTO powders were obtained by solid-state process and sol-gel process. CCTO ceramic samples were prepared by corresponding CCTO powders and sintered at 1080℃ for 4 hours. The obtained sol-gel ceramic samples with average grain size 4 times larger than that of solid-state sample presented an abnormal grain growth. The breakdown field was decreased from 4980 V/cm for solid-state sample to 170 V/cm for sol-gel sample. Besides, the dielectric loss and dielectric constant of the latter are both 19 times higher. It is revealed by the impendence spectroscopy and ε″ curve fitting results that the grain boundary resistance of sol-gel sample (0.272 MΩ) is one third of that of solid-state sample (1.03 MΩ), and the relaxation peak height of the former is about 14 times higher. However, the activation energies of intrinsic relaxation peaks are close for the samples from different synthesis processes. It is concluded that sol-gel process leads to much lower grain boundary resistance and higher relaxation peak height, but exerts little effect on intrinsic dielectric relaxation mechanism of CCTO ceramics.