Electrical properties of Na2SO4-based composite systems

Abstract

Composite electrolytes are well-known multiphase systems and exhibit maxima in the conductivity at certain second-phase concentration. An attempt has been made to investigate a number of sodium sulfate (Na2SO4)-based composite systems. The dispersoids that have been used are MgO, Al2O3, and SiO2. The samples have been characterized using impedance spectroscopy, X-ray diffraction, and differential scanning calorimetry. The maximum conductivity has been observed for MgO dispersed system, and the percolation threshold has been observed at 30-mol% dispersoid, MgO concentration. Interestingly, two maxima have been observed in case of the Na2SO4–SiO2 and Na2SO4–Al2O3 composite systems. In the Na2SO4–SiO2 system, the first maximum occurs at lower concentration, i.e., in the range between 10 and 20 mol%, whereas the second occurs at the 40-mol% dispersoid concentration. For the Na2SO4–Al2O3 system, although slightly indistinguishable, two peaks in the conductivity vs composition plot have been observed around 12- and 30-mol% Al2O3 concentrations.