Influence of polarization and iron content on the transport properties of praseodymium–barium manganite

Abstract

Polarization and iron effects on the electrical properties of Pr0.67Ba0.33Mn1−xFexO3 have been studied using impedance measurements. When iron is introduced, the insulator–metal transition (MI), observed in free compound, disappears and destroying such transition needs an iron concentration less than 5%. We also found that electrical conductance decreases when increasing Fe content. Such results are attributed to the decrease of Mn3+/Mn4+ ratio. Also, they are ascribed to the high probability of encountering Fe3+–O–Fe3+ and Mn3+–O–Fe3+ interactions, which greatly weakens the influence of Mn3+–O–Mn4+ interactions. The AC conductivity studies indicate that different types of hopping are involved. The contribution of hopping mechanism is confirmed by the temperature dependence of the frequency exponent ‘s’. Conductivity analysis shows that small polaron hopping (SPH) and variable range hopping (VRH) models are present in the conduction process. For small iron concentrations (x<0.1), we found that activation energy (Ea) does not changes significantly. Such result is in good agreement with the literature. But, for high iron concentrations (x>0.1), we found that Ea depend strongly in Fe content. We also found in this work that DC-bias does not affect the conduction process but proves its thermal activation. The variation of the conductance with polarization is a proof of an electro-resistance effect.