Structural, electrical and magnetic properties of Sb-doped Pr2/3Ba1/3MnO3 perovskite manganites

We report here the electrical, magnetic and micro-structural features of the Sb-doped (nominally at Mn-sites) Pr2/3Ba1/3MnO3 perovskite manganites. Pristine material shows two insulator–metal (I–M) like transitions in the resistivity–temperature (ρ–T) behaviour. While the higher temperature transition (TP1) at ∼195 K is reminiscent of the usual metal–insulator transition, the lower temperature transition (TP2) at ∼160 K has been ascribed to the grain boundary (GB) effects arising out of the ionic size mismatch between the ions present at the rare-earth site (Pr and Ba). With Sb doping at the Mn-site, both the resistivity peaks are seen to shift to lower temperatures. Room temperature resistivity and the peak values are also successively increasing with Sb doping. Scanning electron micrographs of the samples indicate a gradual increase in their grain sizes with Sb which indicates a gradual decrease in the GB density. The higher temperature insulator–metal transition (TP1) shift is explained on the basis of a competition between double-exchange and super-exchange mechanisms. The observed overall resistivity increase and the shift in the resistivity hump (TP2) with Sb are found related to the gradually decreasing GB density and the ensuing lattice strain increase at the grain boundaries. The intrinsic MR gets suppressed and the extrinsic MR gets enhanced with Sb doping. The observed low temperature resistivity upturn related to the localization of carriers, is also seen to increase with Sb.