Thermal expansion and electrical properties of Fe-doped CaCu3Ti4O12 ceramics

Thermal behavior and electrical properties of Fe-doped CaCu3Ti4O12 ceramics samples have been studied by high-temperature X-ray diffraction, thermal analysis, and impedance spectroscopy. According to X-ray diffraction data, samples of CaCu3Ti4-4xFe4xO12-delta and CaCu3-3xFe3xTi4O12+delta composition do not contain iron-containing impurity phases; in trace amounts may contain copper oxide (II). According to thermogravimetry data, no weight loss of samples was recorded before the melting start temperature (similar to 1033 degrees C). The DSC curves of doped calcium copper titanate samples show an exothermic effect in the range of 506-573 K, not associated with a phase transition, and an endothermic process, at a temperature above 1219 K, due to the dissociation of CuO. The thermal expansion coefficient for CaCu3Ti3,76Fe0.24O12-delta in the range of 298-1193 K changes continuously from 8.6 x 10(6) (298 K) to 11.4 x 10(6) degrees C-1 (1173 K). Based on the results of impedance spectroscopy, the electrical properties of the samples were simulated and an equivalent scheme was proposed. The samples exhibit ionic conductivity. The activation energy of conduction of the CaCu3Ti3.76Fe0.24O12-delta is 0.65 eV and 1.04 eV of the CaCu3-3xFe3xTi4O12+delta.