Electrical Resistivity Behavior and VRH Transport Mechanism in Semiconducting La0.6Sr0.4Mn1−2xFexCrxO3 (0.10≤x≤0.25) Manganites

The transport properties and conduction mechanism in La0.6Sr0.4Mn1−2xFexCrxO3 (0≤x≤0.3) have been investigated. The undoped samples show metal–semiconductor transition with a peak of resistivity at a temperature TP, whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr3+ and Fe3+ ions leads to the increase of resistivity because the simultaneous substitution of Fe3+ and Cr3+ for Mn3+ reduces the number of available hopping sites for the Mn eg↑ electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott’s relation obey the variable range hopping (VRH) mechanism.