Abnormal capacitance voltage behaviors of bismuth-doped CaCu3Ti4O12 ceramics

Ca1−3x/2BixCu3Ti4O12 (x = 0.0, 0.1, 0.2 and 0.3; BCCTO) ceramics were prepared by traditional solid-state sintering method. All samples had pure cubic perovskite-like structure. A drastic grain size reduction was observed with bismuth doping. Dielectric spectra showed two obvious relaxation steps corresponding to two series of peaks in the imaginary part of electric modulus spectra and dielectric loss spectra too. Activation energy fitting by electric modulus spectra reflected different conducting segments in BCCTO ceramics of grains and oxygen vacancies below room temperature. Normalized capacitance dependent of extra bias showed different voltage–capacitance coefficients at special frequencies that suggested multirelaxation mechanisms related with grain and oxygen vacancy. A positive capacitance curvature implies dipolar relaxations in CCTO grains. Whereas a negative curvature suggests oxygen-related relaxations at the interface.