Influence of morphological variations on the microscopic, structural, and magnetotransport characteristics of La0.67Ba0.33MnO3 compounds

In this study, the impact of morphological variations was investigated with respect to the structural, electrical transport, and magnetoresistance properties of La0.67Ba0.33MnO3 manganites, comparing their behaviours at both bulk and nanoscale levels. The structural analysis through Rietveld refinement confirmed the rhombohedral phase crystallization in both samples in R-3c space group. The SEM analysis revealed the crystalline nature of the bulk sample, while the nano sample exhibited particle agglomeration. Additionally, TEM imaging revealed a mean particle size 53.75 nm in the nano sample. The investigation of the metal-insulator transition (TMI) in the nano sample suggests an increase in electron-electron scattering at grain boundaries with diminishing grain size, resulting in a shift of the TMI to approximately 200 K. Below 50 K, the resistivity data indicated a Kondo-like transport behaviour. At the same time, the ferromagnetic-metallic region includes resistivity contributions from grain/domain boundaries, as well as electron-electron and electron-phonon scattering interactions. The conductive behaviour at temperatures above TMI was elucidated through the small polaron hopping (SPH) mechanism and the variable range hopping (VRH) model. Both bulk and nano LBMO samples showed resistivity dominance by grain boundary effects and electron-electron scattering, with the highest MR values recorded as 47.14 and 41.93, respectively, showing a decrease as grain size reduces.