Structural, magnetotransport and morphological studies of Sb-doped La 2/3Ba 1/3MnO 3 ceramic perovskites

Abstract

We report here the structural, magnetotransport and morphological studies of Sb-doped La 2/3Ba 1/3Mn 1− x Sb x O 3 perovskite manganites. Pristine material La 2/3Ba 1/3MnO 3 (LBMO) shows two insulator–metal (I–M) transitions in the electrical resistivity–temperature ( ρ– T) behavior. While the higher temperature transition ( T P1) at ∼340 K is reminiscent of the usual I–M transition in manganites, the lower temperature transition ( T P2) at ∼250 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 (La 3+ and Ba 2+). With Sb-doping T P1 shifts to lower temperatures while T P2 remains invariant up to 3% and shifts to lower temperature for 5%. Room temperature electrical resistivity and the peak values also increase successively with Sb-doping. Scanning electron micrographs of the samples exhibit a gradual increase in their grain sizes with Sb indicating a gradual decrease in the GB density. Shift of T P1 with doping is explained on the basis of a competition between double-exchange and super-exchange mechanisms. The overall electrical resistivity increases and the shift in the electrical resistivity hump ( T P2) with Sb-doping is found related to be gradually decreasing GB density and the ensuing lattice strain increase at the GBs. The intrinsic magnetoresistance (MR) gets suppressed and extrinsic MR gets enhanced with Sb-doping. At T> T P1, the electrical resistivity is found to follow the adiabatic polaron hopping model whereas the electron–magnon scattering is found to dominate in the metallic regime ( T< T P1).