Impact of the sintering temperature on the structural, magnetic and electrical transport properties of doped La0,67Ba0,33Mn0,9Cr0,1O3 manganite

Abstract

A systematic investigation of the La0,67Ba0,33Mn0,9Cr0,1O3 perovskite has been undertaken, mainly to understand the impact of the sintering temperature on the structural, microstructural, magnetic and electrical transport properties in these materials. The La0,67Ba0,33Mn0,9Cr0,1O3 manganite was sintered by a solid-state route at 1000°C, 1200°C and 1400°C. The X-ray diffraction studies show that all samples crystallize with the rombohedral symmetry within the space group R3¯C, regardless of the sintering temperatures employed in this work. The MnOMn bond angle decreases and the MnO bond length increases with the increase of the grain size. All samples undergo a paramagnetic (PM)–ferromagnetic (FM) phase transition at T=TC. Both the magnetization and the Curie temperature TC decrease with increasing grain size mainly due to the increase of the MnO bond length dMnO. The electrical resistivity (ρ) increases with decreasing grain size because of the enhancement of the grain boundary effect. Low temperature resistivity data below TC was fitted by the relation ρ=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of the grain/domain boundary, the electron–electron scattering effects and, to a lesser extent, the electron–(magnon,phonon) scattering effects in the mechanism of conduction. On the other hand, the high temperature resistivity above the metal–insulator (M–I) transition Tp for the sample sintered at 1000°C was explained using variable range hopping (VRH) and small polaron hopping (SPH) models. IR studies revealed that the vibration mode at 411cm−1, associated with the internal bending of MnO6 octahedra, becomes softer, indicating an increase of the distortion.