Effect of low nickel substitution on structure, morphology, and electrical transport of La_0.7Sr_0.2Ba_0.1Mn_{1- x} Ni _x O₃ (x=0.02 and 0.05)

The effect of low nickel substitution at Mn-site on structure, microstructure and electrical transport properties of La_0.7Sr_0.2Ba_0.1Mn_{1- x} Ni _x O₃ (x = 0.02 and 0.05) were investigated. Samples were prepared by sol-gel method. From Rietveld refinement result, crystal structure of both samples were found to be Rhombohedral with R-3c (167) space group. Low nickel substitution at Mn-site shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increase which can link to Jahn-Teller distortion and double exchange. Scanning electron microscope (SEM) result reveals that nickel substitution leads to smaller grain size. Temperature-dependent resistivity ρ(T) has been measured at 15-285 K with zero field cooling. The experimental resistivity data were fitted by Percolation model. Percolation model can describe the electrical behavior of both samples based on electron-electron, electron-magnon, and electron-phonon scattering, and Kondo-like spin-dependent scattering at low temperature and adiabatic small polaron hopping at high temperature. It was found that nickel substitution decreases the metal-insulator transition temperature (T_M-I) from around 304 to 272 K, and Curie temperature (T_c) from around 330 to 310 K.