Structural and impedance spectroscopic studies of spark plasma sintered CaCu_3Ti_4O_(12) dielectric ceramics: an evidence of internal resistive barrier effect

摘要

A giant dielectric constant CaCu_3Ti_4O_(12) ceramic was prepared by solid-state reaction route. Powders were spark plasma sintered at 1050 ℃ for 30 min. Rietveld refined XRD pattern reveals the formation of pure phase cubic perovskite CCTO. The dielectric properties were characterized in a broad frequency range of 10 Hz-8 MHz at temperatures 20-120 ℃. The grain size of sintered pellets was found in range of 12-15 μm. Impedance spectroscopic analysis shows that the observed semicircle in the Cole-Cole plot was associated with grain boundary relaxation effect. This study reveals that there is an evidence of internal resistive barrier which responsible for a giant dielectric constant in CaCu_3Ti_4O_(12) ceramic. An Arrhenius temperature dependent relaxation effect was observed in grain boundary. Using the characteristic frequency of relaxation peak, grain boundary capacitance was calculated to be 0.27 μF. It was found that on increasing the temperature, the resistance of grain boundaries was decreased rapidly as compared to that of the grains. The activation energy of grain boundary was calculated to be 0.165 eV.