On the Various Approaches to Enhancing the Conductivity of Sodium Sulfate: Review and Current Developments

Author： Gopalan P. Saha S. Bobade S. Kulkarni A.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.155, Iss.1, 2000-11, pp. : 154-167

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Abstract

The various approaches to enhancing the conductivity of Na₂SO₄ are reviewed. The role of the size of the dopant cation on the conductivity enhancement has been emphasized. As for anion doping, apart from the size, the role of the shape and orientational ordering of the dopant ion has been highlighted. The structure of the guest ion appears to influence the stabilization of Na₂SO₄–I at low temperatures. A recent development has been the formation of Na₂SO₄-based composites. In this work, the stabilization of the Na₂SO₄–I phase for the 4 m/o La₂(SO₄)₃ composition in the Na₂SO₄–La₂(SO₄)₃ system has been established at 120°C through structural evidence. Several new features appear in the conductivity behavior of the Na₂SO₄–Al₂O₃ composite system. In contrast to a previous study, we now observe and report the formation of the high conducting Na β-alumina phase for the 5 m/o Al₂O₃ composition. As before, two peaks are observed in the conductivity–composition plot, a feature not commonly encountered in known composite systems. Unlike other composite electrolyte systems, the size of the dispersoid phase does not appear to affect the conductivity enhancement. Furthermore, in most known systems, γ-Al₂O₃ is used as a dispersoid. However, enhancements in conductivity for the Na₂SO₄–Al₂O₃ system have been observed only when the identified phase is α-Al₂O₃.