Role of Relaxation on the Giant Permittivity and Electrical Properties of CaCu3Ti4O12 Ceramics

CaCu3Ti4O12 (CCTO) ceramics were synthesized under various sintering conditions to investigate the role of relaxation on permittivity and electrical properties. Two relaxation processes that respectively related to grain and to domain boundary at a temperature as low as 223 K were fitted according to the Cole-Cole theory. The results indicate that both relaxations largely account for the giant permittivity of CCTO ceramics. Moreover, the relaxation behaviors of grain and of the grain boundary can be processed via impedance plots that vary from 113 K to 473 K. It is shown that longer sintering duration leads to lower resistance of grain and of grain boundary: e.g., from 3200 Omega to 810 Omega and 1.76 M Omega to 0.48 M Omega, respectively. The activation energy related to grain-boundary relaxation drops from 1.14 eV to 0.80 eV, while the value of grain stays unchanged at about 0.11 eV. The Schottky barrier of the CCTO sample decreases from 0.65 eV to 0.57 eV. It is also proposed that the nonlinearity of current-voltage property for CCTO ceramics may be strongly related to the relaxation processes of grain boundaries.