Various approaches to the enhancement of the conductivity of Na2SO4 were reviewed. The effect of the size of the dopant cation upon conductivity enhancement was emphasized. In the case of anion doping, the roles played by the shape and orientational ordering of the dopant ion were also highlighted. The structure of the guest ion appeared to affect the stabilization of Na2SO4 at low temperatures. A new development was the formation of Na2SO4-based composites. Stabilization of the Na2SO4-I phase in a 4mol%La2(SO4)3 composition at 120C was established here. Several new features appeared in the conductivity behavior of the Na2SO4-Al2O3 composite system. The formation of a high-conductivity Na β-alumina phase in a 5mol%Al2O3 composition was reported. Two peaks were observed in the conductivity versus composition plot. This feature was not usually encountered in known composite systems. Unlike other composite electrolyte systems, the size of the dispersoid phase did not appear to affect the conductivity enhancement. In most known systems, Al2O3 was used as a dispersion. However, enhancements in conductivity of the Na2SO4-Al2O3 system were observed only when the identified phase was α-Al2O3.

On Various Approaches to Enhancing the Conductivity of Sodium Sulfate - Review and Current Developments. P.Gopalan, S.Saha, S.Bobade, A.Kulkarni: Journal of Solid State Chemistry, 2000, 155[1], 154-67