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 (Na 2 SO 4 )-based composite systems. The dispersoids that have been used are MgO, Al 2 O 3 , and SiO 2 . 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 Na 2 SO 4 -SiO 2 and Na 2 SO 4 -Al 2 O 3 composite systems. In the Na 2 SO 4 -SiO 2 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 Na 2 SO 4 -Al 2 O 3 system, although slightly indistinguishable, two peaks in the conductivity vs composition plot have been observed around 12-and 30-mol% Al 2 O 3 concentrations.

Structural, electrical conductivity and dielectric behavior of Na2SO4–LDT composite solid electrolyte

“…3 displays the DTA curves of the pure and LDT doped Na 2 SO 4 samples with the heating rate of 20 °C/min. The thermogram of the pure Na 2 SO 4 shows that the endothermic peak at the temperature 250 °C corresponds to the phase transition from phase V → I [19]. It is interesting to note that, introduction of LDT components into the crystal lattice of Na 2 SO 4 induces small changes i.e.…”

“…Several theoretical models such as space charge layer model, defect-induced order–disorder phase model and random resistor model have been developed by various investigators, satisfactorily explaining the phenomenon of composites in the field of solid state ionics [17], [18]. The ionic salt Na 2 SO 4 undergoes a phase transition from room temperature phase V to phase I during heating at 250 °C whereas cooling the phase I it transforms to phase III, which subsequently leads to phase V [19]. In this study a series of LDT doped Na 2 SO 4 samples i.e.…”