Preparation of CaCu_3Ti_4O_(12) ceramics with low dielectric loss and giant dielectric constant by the sol-gel technique

摘要

CaCu_3Ti_4O_(12) 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 0.60mol/L, the pH value of the sol was 1.58, and the aging time of the sol was 6 h. After sintering at 1100℃for 15 h, the CCTO ceramics with the highest density and fine-grained microstracture were obtained, exhibiting outstanding dielectric properties: ε≈3.50 ×10~4 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℃. The complex, impedance spectroscopy analysis suggested that the obtained CaCu_3Ti_4O_(12) 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.