Influence of Fabrication Parameters on the Phase Formation and Dielectric Properties of CaCu ₃Ti ₄O ₁₂ Ceramics

The giant dielectric permittivity materials CaCu ₃Ti ₄O ₁₂ (CCTO) were synthesized by conventional solid-state reaction techniques. X-ray diffraction and Raman scattering for the powder indicate that the powder calcined at 950 °C for 12 h has been completely transformed into the purer CCTO phase. Furthermore, the morphology and size of the grains of the ceramics sintered at 1090 °C in the dwell time range from 0 to 26 h were observed by scanning electron microscopy (SEM). Dielectric properties of the polycrystalline CCTO ceramics were characterized in a broad frequency range (100 Hz-1 MHz) and at a temperature ranged from 300 to 500 K. The longer sintering time may lead to more defect structures and the enhanced conductivity, also leads to substantial improvements in permittivity. Grain size and density differences were not large enough to account for the enhancement in dielectric permittivity. Based on the observations, it is believed that the primary factor affecting dielectric behavior is the development of internal defects. The CCTO ceramics sintered at 1090 °C for 15 h exhibit lower dielectric loss (∼0.05) near room temperature, and the dielectric relaxation behavior above 1 kHz was observed to follow the Arrhenius law. The activation energy (E _a) of 0.65 eV indicates that the doubly ionized oxygen vacancies in the grain boundaries are responsible for the dielectric relaxation of the CCTO ceramics.