Gd doping effect on impedance spectroscopy properties of sol-gel prepared Pr0.5-xGdxSr0.5MnO3 (0 ≤ x ≤ 0.3) perovskites

The electrical and dielectric properties of Pr0.5-xGdxSr0.5MnO3 (0 ≤ x ≤ 0.3) manganites prepared by the conventional sol-gel method have been studied in a wide range of temperature [80-320 K] and frequency [40-107 Hz] using impedance spectroscopy technique. DC conductivity (σDC) results show that for x = 0, 0.1 and 0.2, the samples present a semiconductor behavior in the temperature range of the study. For x = 0.3, a semiconductor-metal transition is observed at 280 K. σDC shows also a decrease in the conductivity with the increase of Gd doping. The calculated activation energies are Gd content dependent. AC conductivity results were analysed using Drude model in the metallic region and by the Jonsher power law in the semiconductor one. The Niquist plots for x = 0.2 and x = 0.3 obeys at Cole-Cole model. The impedance spectra were fitted by an adequate equivalent circuit involving two contributions attributed to grains and grain boundaries associated with an inductance. Such a result reveals a correlation between electrical and magnetic properties of Gd-doped manganites. In addition, grain-boundary resistance shows a major contribution at higher temperature. High dielectric constants are obtained in particular at low frequencies. Dielectric loss is analyzed through the Giuntini theory with which we have calculated the energy required for charge carriers to hope over the potential barriers.