Giant dielectric-permittivity property and relevant mechanism of Bi2/3Cu3Ti4O12 ceramics

A series of Bi2/3Cu3Ti4O12 (BCTO) ceramics were prepared via conventional solid-state reaction under different sintering temperature conditions. Their microstructures, crystalline structures and dielectric and electrical properties were investigated. It has been found that all of the BCTO ceramics show giant dielectric-permittivity values with low frequency ɛ′ larger than 1.5 × 105 at room temperature. There exist two relaxations in the dielectric dispersion spectra and three semicircles in the complex impedance plane. In general, BCTO ceramics are qualitatively quite similar to CaCu3Ti4O12 (CCTO) ceramics in the aspect of dielectric and electrical properties. However, unlike CCTO ceramics, BCTO ceramics possess the dense microstructures of small and uniformly distributed grains, which are insensitive to sintering temperature conditions. From analysis, we attribute the dielectric relaxation in the high frequency region to an internal barrier layer capacitance (IBLC) effect associated with insulating grain boundaries and semiconducting grains and the other one in the low frequency region to an electrode polarization effect due to the Schottky barriers formed at electrode-ceramic interfaces.