Effects of dc bias on dielectric relaxations in CaCu₃Ti₄O₁₂ ceramics

Effects of dc bias on dielectric relaxations in CaCu₃Ti₄O₁₂ ceramics were investigated via an improved dielectric spectroscopy. A new low-frequency dielectric relaxation, which was assigned to space charge polarization, was found shifting towards higher frequency with increasing bias voltage in the improved spectra. It was suggested that the Schottky barrier at grain boundary was lowered under dc bias resulting in higher possibility for carriers to migrate. Therefore, the relaxation time was decreased, which was in accordance with rightward shift of this relaxation under increased dc bias. In addition, dependence of the widely reported high-frequency relaxation (> 10⁵ Hz) and middle-frequency relaxation (10³–10⁵ Hz) on bias voltage was also discussed. Permittivity contributed by either high-frequency or middle-frequency relaxation presented inverse dependence on dc bias. Discrepancy on barrier parameters was obtained assuming both of them physically correlated with the barrier at grain boundary.