T. Vijay Kumar, R. Swarnalatha, A. Sadananda Chary and S. Narender Reddy
Mixed systems [NaNO3]100-x:[Sr(NO3)2] x with x = 0, 4.27, 9.12, 14.68 and 21.12 in different mole percentages were grown by slow evaporation method. Pellets of these crystals were prepared by applying suitable pressures and sintered at 200 0C for 20 hours. In the present study, the variation of DC ionic conductivity with temperature on these mixed matrix solid electrolytes has been measured in both single crystal and pellet forms and it is found to increase with temperature in all the systems. Enhancement of conductivity is noticed to increase with mole percent (m/o) in NaNO3-Sr(NO3)2 mixed systems. The maximum enhancement of conductivity is observed to be nearly one order of magnitude with respect to the host material in single crystals as well as pellets for x = 14.68. In all the systems the conductivity in the pellet form is found to be higher than that of single crystal form. Analysis of the Xray diffraction peaks shows the co-existence of two phases i.e. NaNO3 in rhombohedra phase and Sr(NO3)2 in fluorite type phase. The experimental data indicating higher conductivity at x = 14.68 is interpreted in terms of the increased defect concentration at phase boundaries which are the regions of misfit of disorder, the movements of atoms along the boundaries can be expected to occur easily and also the increase of defect concentration at the phase boundaries. Further, decrease in conductivity is explained in terms of the reduction of phase boundaries and decreasing of free volume available for Na+ ion transport. Activation energies are obtained from the conductivity data in the extrinsic conduction region
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