Microstructure and dielectric property of hot-pressed high density CaCu3Ti4O12 ceramics

High density CaCu3Ti4O12 ceramics has been prepared by the hot-press sintering technique under ambient atmosphere. Its microstructure, crystalline structure and dielectric property are investigated and compared with those of the conventionally sintered ceramics. While the conventionally sintered ceramics show generally the theoretical relative densities lower than 95.0%, the hot-pressed one with a short sintering duration reaches the value of 99.3% and exhibits the microstructure of very uniform grain size distribution with the average large grain size of about 3 μm. X-ray diffraction analysis shows that there are Cu2O minor phases in the hot-pressed ceramics whereas no secondary phase exists after a further thermal treatment in ambience. Both the hot-pressed ceramics and its further thermally treated one exhibit two dielectric relaxations at room temperature, whereas the conventionally sintered ceramics have only one dielectric relaxation. Moreover, the hot-pressed CCTO ceramics has an extremely large low-frequency permittivity of 4.3 × 105, which further increases to nearly 2 × 106 through the ambient thermal treatment. The relation between microstructure and dielectric property is discussed.

► The high density CCTO ceramics are prepared by hot-press sintering technique.
► The HP ceramics exhibit an extremely high ε′ of 4.3 × 105 and two relaxations at RT.
► Previous model could well explain the dielectric dispersions in HP ceramics.