Anomalous relaxation behaviour in La_0.7Sr_0.3MnO₃ (LSMO)-ZnO nanocomposite

Abstract The temperature-dependent relaxation behaviour and the conduction mechanism in LSMO-ZnO nanocomposite have been studied by employing complex impedance spectroscopic techniques. The imaginary part of impedance exhibits a relaxation phenomenon, with the relaxation frequency showing a Gaussian-like dependence on temperature. At temperatures below 340 K the relaxation frequency increases with increase in temperature due to the reduction in grain and grain boundary resistances. However, an unusual decreasing nature of relaxation frequency with increase in temperature, above 358 K, is observed. This feature is explained in terms of an increased value of the grain boundary capacitance owing to a transition from bipolaron hopping to single polaron hopping. Such anomalous relaxation behavior makes the nanocomposite a suitable candidate for applications in sensors, switches, actuators etc. The dispersion behavior of the AC conductivity is explained with Jonscher’s law involving small polarons. The study confirms that the correlated barrier hopping (CBH) is the dominant dynamic process involved in the AC conduction mechanism in LSMO-ZnO nanocomposite across the measured range of temperature.