Large breakdown field and dielectric performance of CaCu3Ti4O12 ceramics modified by Al2O3

CaCu₃Ti₄O₁₂ ceramics samples with varied Al₂O₃ additions have been prepared by a dispersion-precipitation-sintering method. The ceramics with nominal addition of 8 wt% Al₂O₃ sintered at 1100°C for 4 hours shows a breakdown electric field E_b of 21 kV/cm, compared with reported values of 1.0~2.0 kV/cm. Three energy levels of dielectric relaxation, two of which do not vary with either second phase addition or sintering condition, are found. The nearly constant levels of ~0.13 eV and ~0.33 eV are considered to relate to bulk and domain boundary relaxations. Another level varied from 0.61 to 0.84 eV is suggested to be Maxwell-Wagner relaxation of grain boundary, which correlates well with breakdown electric field E_b. It was proposed that the enhanced breakdown field is attributed to higher energy level of grain boundary relaxation and CuAl₂O₄ aggregation in the intergranular region.