The discovery of inorganic solids with ionic conductivities comparable to those of aqueous electrolytes has revolutionized solid-state electrochemistry. Sodium beta alumina, a Na(+) conductor, and LixTiS(2), an intercalation compound with simultaneous Li(+) and electronic conductivity, are two of the best and most versatile fast ionic conductors. A wide variety of cations can replace Na(+) in beta alumina and Li(+) in LixTiS(2) and change the properties of the materials. Sodium beta alumina and LixTiS(2) are currently used in the development of high-energy density batteries for electric vehicles and electrical utility load leveling. Current research in solid ionic conductors is exploring new intercalation compounds, solid polymer electrolytes, and alkali ion and proton transport in crystalline solids.

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This paper presents measurements of ionic conductivity in single crystals of Li + and mixed Li+/Na+ beta alumina. The crystals were prepared by ion exchange of Na + beta alumina crystals in LiC1, LiNO3, or LiNO3 with NaNO3 added. The measured room temperature conductivity of Li + beta alumina, about 3 X 10 -8 ~-i cm-i, is higher than earlier values. The activation energy was found to be 0.24 eV from --80 ~ to 400~ Room temperature conductivities of Li+/Na + beta alumina crystals pass through a minimum as the composition is varied from pure Na + to pure Li + beta alumina. The activation energy achieves a maximum at the same composition. The theory of Hendrickson and Bray for mixed-alkali conduction in glasses is adapted to explain this effect. The deleterious effect of water on lithium transport in beta alumina is also examined.

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