Influence of grain size on the electrical properties of the double-layered LaSr2Mn2O7 manganite

The double-layered LaSr2Mn2O7 manganite was synthesized by the sol–gel process. Two samples with the average grain size from ∼150nm to ∼1μm were prepared by controlling the sintering temperature. Both samples had a tetragonal structure, with a small fraction of impurity phase in the S-1250 sample. In order to investigate the probable influence of grain size on the conduction mechanism, resistivity of the samples was measured as a function of temperature, and the data obtained was analyzed by different conduction mechanisms. It was found that with increase in the grain size, resistivity decreased at all temperature ranges. The results show that the adiabatic small polaron hopping (SPH) model is probably responsible for conduction at high temperature range, and that the 3D variable range hopping (VRH) model shows a better correlation with the experimental data for low temperature range. These analyses indicate the influence of grain size on the parameters obtained from fitting the data by both models. ► LaSr2Mn2O7 was synthesized with nano and micro grain sizes by the sol–gel process. ► The grain size effects on hopping were studied by analyzing of the resistivity data. ► The data was fitted by SPH model at above θD/2 and 3D and 2D VRH models at T