Impedance spectroscopy study of the electrical properties of composites of CaCu3Ti4O12-CuO

Abstract

Calcium copper titanate Cacu3Ti4O12 attracts considerable attention of researchers due to the manifestation of extremely high values of dielectric constant (ε ~104 -105) in wide temperature (100 - 600 K) and frequency (from 20 Hz to 1 MHz) ranges. In spite of the active studies of CaCu3Ti4O12, there are unresolved questions on the influence of microstructure, the presence of copper (II) oxide layers in the intergrain space of the ceramics and on the selective influence of paramagnetic dopants on the electrophysical properties of the compound. In this connection, the electrical properties of the CaCu3Ti4O12-CuO composite were studied by the method of impedance spectroscopy. The composite was synthesized by the solid-phase method of staged calcination at 650°C, 850°C and 1050°C for 50 hours. The analysis of the impedance spectroscopy results has shown that CaCu3Ti4O12-CuO is a material with mixed electron-ion conductivity. The strong dispersion of the conductivity at room temperature was explained by the polarization of copper ions or protons, which can be present in the sample due to the dissociative adsorption of water molecules from the air. The minimum of the dispersion of the dielectric constant was found at a temperature of about 300°C, which was explained by the appearance of oxygen conductivity substantially neutralizing the cation conductivity. The simulation of electrical properties by the method of constructing equivalent circuits showed that the sample consisted of two layers. The high-resistivity layer was assigned to the crystalline part of the sample, and the low-resistivity layer to the intergranular part. The significant change in the electrical properties of the sample at the temperature of 200 - 225°C is not associated with the occurrence of a phase transition in it.