Impedance spectroscopy of CaCu3Ti4O12

Nowadays, due to an increased demand for miniaturization of electronic devices, electrotechnical ceramics exhibiting giant permeability, in particular, calcium copper titanate CaCu3Ti4O12 (CCTO), gain a considerable scientific interest of researchers around the world. Even though this is not a ferroelectric material, the compound demonstrates very high dielectric permeability (epsilon similar to 10(4) - 10(5)) within wide temperature (100 - 600.) and frequency (20 Hz-1 MHz) ranges. Notwithstanding intensive studies on CaCu3Ti4O12, some of problems related to the effect of structural inhomogeneities of ceramics microstructure on electric properties of the compound remain open. As one can see from the experimental data, the traditionally analyzed electrical parameters of materials, such as the loss tangent of dielectric or permeability, show not only a dependence on the temperature or frequency of the electromagnetic field, but also on the geometrical parameters of samples due to the microstructure inhomogeneity of compound. As a result, on an example of CaCu3Ti4O12, integral parameters of media obtained through impedance spectroscopy are proposed for the use. The parameters under study have a clear physical meaning and do not depend on the geometry of the samples. The study proposes an equivalent circuit adequately describing electric properties of calcium copper titanate. The structure of the CaCu3Ti4O12 equivalent circuit reveals three processes possible within the material - through-thickness conductivity and two overlapping polarization processes - electronic and dipole relaxation. The temperature dependencies of the specific conductivity in the Arrhenius scale for CaCu3Ti4O12 samples of different thicknesses are linear and are characterized by an activation energy of 1.05 eV. The temperature dependencies of electric parameters of the samples exhibit minima at T = 350 degrees C, which can be explained by the change in the polarization mechanism. It has been hypothesized that bipolar ionic conductivity created by oppositely charged ions occurs. The formation of electrically neutral associates of such ions cause the extremum of the electric parameters of the samples.