Conduction mechanism in La0.67Ba0.33Mn1−xFexO3 (x=0–0.2) perovskites

We have investigated the mechanism of conduction in relatively high iron doped manganites La0.67Ba0.33Mn1−xFexO3 (0≤x≤0.2). Below 10% of Fe3+ content these materials show metal–semiconductor transition with a peak of resistivity (ρmax) at a temperature TP, whereas above 10% of Fe3+ concentration they exhibit only semiconductor behaviour. Interestingly TP for the undoped compound is very close to room temperature (297 K) and decreases with doping rates (230 and 114 K for x=0.05 and 0.1, respectively). Low temperature resistivity (ρ) data below TP have been relatively well fitted with the relation ρ(T)=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of grain/domain boundary, electron–electron scattering effects and to a lesser extent electron–(magnon, phonon) scattering effects in the conduction of these materials. On the other hand the high temperature resistivity data (T>TP) were explained using variable range hopping (VRH) and small polaron hopping (SPH) models. Changes in resistivity variation have been analysed on the basis that the substitution of Fe3+ for Mn3+ reduces the number of available hopping sites for the Mn eg↑ electron and suppresses the double exchange (DE), rather than on the basis of lattice effect which is insignificant due to similar ionic radii of Fe3+ and Mn3+.