Effects of pH and sintering temperature on the synthesis and electrical properties of the bilayered LaSr2Mn2O7 manganite prepared by the sol-gel process

The bilayered LaSr2Mn2O7 manganite was synthesized by the sol-gel process at different pH values (3.5, 7, and 9.5) and different sintering temperatures (1553, 1623, and 1723 K) to investigate the effects of growth conditions upon the structural and electrical properties of the samples under investigation. X-Ray diffraction and FT-IR spectroscopy techniques confirm the phase formation for all samples. However, samples sintered at 1553, 1623, and 1723 K, and formed at pH = 7 are single phased having a tetragonal structure. Study of these single-phased samples indicates that with increase in the sintering temperature from 1553 to 1723 K, the average grain size increases from similar to 200 to similar to 1000 nm. To investigate the influence of grain size on the conduction mechanism, resistivity of the samples was measured as a function of temperature. The data obtained was analyzed by the adiabatic small polaron hopping model. These analyses show the influence of grain size on the parameters obtained by fitting the data by the above models.