Influence of particle size on electrical transport properties of $La_{0.67}Sr_{0.33}MnO_3$ manganite system

A systematic investigation of lanthanum-based manganite, $La_{0.67}Sr_{0.33}MnO_3$, has been undertaken with a view to understand the influence of varying particle sizes on electrical transport properties. With a view to obtain materials with varying particle size, they were prepared by sol-gel route, sintering at four different temperatures. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD data has been analyzed by Rietveld refinement technique and it has been confirmed that the materials have rhombohedral crystal structure with R (3) over barc space group. Metal-insulator transition temperatures $(T_p)$ were found to decrease continuously with decreasing particle size where as ferro to paramagnetic transition temperatures $(T_c)$ are found to remain constant. The magnetoresistance (MR) values are found to increase with decreasing particle size. With a view to understand the conduction mechanism, the electrical resistivity data have been analyzed both in the ferromagnetic metallic $(T < T_p)$ as well as high temperature paramagnetic insulating $(T > T_p)$ regions