Effects of Charge Compensation on Colossal Permittivity and Electrical Properties of Grain Boundary of CaCu(3)Ti(4)O(12) Ceramics Substituted by Al(3+) and Ta(5+)/Nb(5+)

The effects of charge compensation on dielectric and electrical properties of CaCu(3)Ti(4-x)(Al(1/2)Ta(1/4)Nb(1/4))(x)O(12) ceramics (x = 0−0.05) prepared by a solid-state reaction method were studied based on the configuration of defect dipoles. A single phase of CaCu(3)Ti(4)O(12) was observed in all ceramics with a slight change in lattice parameters. The mean grain size of CaCu(3)Ti(4-x)(Al(1/2)Ta(1/4)Nb(1/4))(x)O(12) ceramics was slightly smaller than that of the undoped ceramic. The dielectric loss tangent can be reduced by a factor of 13 (tanδ ~0.017), while the dielectric permittivity was higher than 10(4) over a wide frequency range. Impedance spectroscopy showed that the significant decrease in tanδ was attributed to the highly increased resistance of the grain boundary by two orders of magnitude. The DFT calculation showed that the preferential sites of Al and Nb/Ta were closed together in the Ti sites, forming self-charge compensation, and resulting in the enhanced potential barrier height at the grain boundary. Therefore, the improved dielectric properties of CaCu(3)Ti(4-x)(Al(1/2)Ta(1/4)Nb(1/4))(x)O(12) ceramics associated with the enhanced electrical properties of grain boundaries. In addition, the non-Ohmic properties were also improved. Characterization of the grain boundaries under a DC bias showed the reduction of potential barrier height at the grain boundary. The overall results indicated that the origin of the colossal dielectric properties was caused by the internal barrier layer capacitor structure, in which the Schottky barriers at the grain boundaries were formed.