Origin of Giant Dielectric Permittivity in CaCu_3Ti_4O_(12) Ceramics

CaCu3Ti4O12(CCTO) is one typical giant dielectric material with large e′ value in the order of 104,however,origin of giant dielectric permittivity in it is still controversial so far.In order to explore its possible origin,the dielectric properties and complex impedance of CCTO ceramics prepared via solid-state reaction method were investigated.Within the frequency range of 40 Hz?100 MHz,only one Debye-type relaxation around 1 MHz is ob-served at room temperature,while high-temperature dielectric dispersion shows two Debye-type relaxations below 1 kHz and around 1 MHz,respectively.The same sample surface-polished with Ag-paint electrodes and sputtered Au electrodes is measured at high temperature,respectively.It is revealed that the dielectric relaxation in the low frequency range changes significantly with the type of electrodes,while the dielectric relaxation in the high fre-quency range is independent of the type of electrodes,but exists closely relationship with the microstructure of samples.The two dielectric relaxations are thus suggested to originate from an electrode polarization effect and an internal barrier layer capacitance effect associated with insulating grain boundaries and semiconducting grains,re-spectively.