Change of conduction mechanism in the impedance of grain boundaries in Pr0.4Ca0.6MnO3

Abstract

Freshly synthesized polycrystalline Pr0.4Ca0.6MnO3 sample has been analyzed by employing X-ray diffraction, magnetization and impedance spectroscopic techniques. Magnetization M(T) showed charge ordering (TCO) around 268K and below this temperature variation of magnetic and electric field effects is discussed. With the decrease of temperature, the change in the size and shape of the impedance plane plot is explored in terms of modulation of different relaxation processes. An equivalent circuit model (RQ) is used to determine the electrical parameters of Pr0.4Ca0.6MnO3 sample at different temperatures. Impedance of grain boundaries derived from the fitting of experimental data using an equivalent circuit model shows a change in conduction mechanism from small polaron hopping (SPH) to the variable range hopping (VRH) model around 148K. Activation energies calculated from the SPH model and relaxation frequencies of imaginary part of impedance are compared and discussed. Average normalized change (ANC) deduced from the impedance data illustrates a change in conduction mechanism around 148K due to the superexchange networks of Mn3+ and Mn4+.