Preparation of CaCu3Ti4O12 ceramics with low dielectric loss and giant dielectric constant by the sol-gel technique

CaCu3Ti4O12 precursor powders were synthesized by the sol-gel process. The optimized processing parameters for the synthesis of precursor powders were as follows: the Ti concentration was 0.60 mol/L, the pH value of the sol was 1.58, and the aging time of the sol was 6 h. After sintering at 1100 °C for 15 h, the CCTO ceramics with the highest density and fine-grained microstructure were obtained, exhibiting outstanding dielectric properties: ε′≈3.50×104 and tan δ=0.014 (at 1 kHz). The low dielectric loss was attributed to the highest grain boundary resistance which significantly reduced the leakage current across grain boundaries. A broad dielectric relaxation peak was observed around 300 °C. The complex impedance spectroscopy analysis suggested that the obtained CaCu3Ti4O12 ceramics were electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. The calculated grain boundary resistance and grain resistance were 0.87 MΩ and 3.50 Ω, respectively.