Specific features of the dielectric spectrum of CaCu$_3$Ti$_4$O$_{12}$ in the low-frequency range

The dielectric spectra of CaCu$_3$Ti$_4$O$_{12}$ ceramics with giant values of the dielectric constant have been presented. The spectrum exhibits Debye dispersion with an activation energy of 0.075 eV in the high-frequency range of 10$^6$–10$^7$ Hz, and a characteristic plateau has been seen in the frequency dependence of the dielectric constant in the range of 10$^4$–10$^5$ Hz. A considerable increase in the loss factor $\varepsilon''$ has been observed in the low-frequency part of the spectrum and a capacitive-to-inductive impedance transition has been revealed in some samples at a frequency below 10$^{-2}$ Hz. The causes of this transition have been discussed.