Ionic Transport Behavior in Na₂SO₄-Li₂O-MoO₃-P₂O₅ Glassy System

Abstract

The need for electrolytes suitable for energy storage has spurred investigations into a number of lithium, silver and sodium ion conducting inorganic glass systems. It is apparent that two strategies have been used in the design of ion conducting electrolytes. The first is to use a combination of two anionic species which has been known to give increased ionic conductivity and is attributed to the so-called mixedanion effect. The second strategy is to dissolve ionic cation salt in a conventional polymeric silicate, borate or phosphate glass containing a same cation. The increased conductivity is attributed to a volume increasing effect of the dissolved ionic salt. Several studies have been reported on lithium phosphate glasses to which lithium halides and lithium sulphate have been added. However, there has been no experimental results for the introduction of sodium sulphate into the lithium phosphate network. How specifically this feature – mixed alkali in the presence of sulphate ion — influences ion transport in the glasses is unclear. It is therefore necessary to investigate the ion transport behaviour of Na₂SO₄ containing lithium phosphate glasses in order to understand better the role of Na₂SO₄ in the ionic cation transport in these glasses. In this paper we report both dc and ac conductivity measurements performed on the 0.5[xNa₂SO₄-(1-x)Li₂O]-0.5[0.4 (MoO₃)₂-0.6P₂O₅] glasses with x varying between 0 and 1. The complex impedance data is analyzed in conductivity and electric modulus formalism in order to throw light on transport mechanism. The glass composition relative to (x = 0.5) has exhibited a decreasing in the conductivity of about two orders of magnitude compared to the simple end glasses (x = 0, 1). This behaviour is associated with the mixed alkali effect (MAE). It could be attributed to the fact that the two types of alkali ions are randomly mixed and have distinct conduction pathways.