Temperature dependence of dielectric properties for copper doped magnetite

Samples with the chemical formula CuxFe3-xO4+delta (x = 0.2, 0.4, 0.6, 0.8, 1 and 0 <= delta <= 0.4; delta = 0.5-0.5x) were prepared by the standard ceramic method. The ac conductivity (sigma(ac)) and dielectric loss tangent (tan delta) are measured. Both the dielectric constant (epsilon(')) and dielectric loss (epsilon{''}) are calculated in the temperature range from room temperature up to 773 K at different fixed frequencies. The measurements showed that the ac conductivity increases with both temperature and frequency and becomes frequency-independent at high temperatures. An abnormal behaviour was observed for the dielectric constant curves. The increase in epsilon' with increasing temperature is ascribed to the thermal energy that given to the system allows more dipoles to be free and the field orient them in its direction. The dielectric loss tangent tan delta curves exhibits a dielectric relaxation peaks. The first peak is assigned to copper-ferrite phase transition (tetragonal-cubic) and the other to ferromagnefic phase temperature (Curie temperature). It was observed that the second transition peak shifted towards lower values by increasing frequency. The relaxation frequency FD was shifted to lower values as the frequency increases. The activation energy for dielectric relaxation ED is generally increases as CU2, ion substitution increases. (c) 2006 Elsevier B.V. All rights reserved.