In 1971 Bob Huggins and I presented a paper at NBS, titled as above*. Little did we realize how prophetic our title would be. The remarkable ion transport properties of the beta alumina family not only led to searches for other ion conducting solids, but also to the use of mixed conducting materials as electrodes for electrochemical cells and shortly thereafter to the use of mixed conducting intercalation compounds for rechargeable lithium batteries.

The studies at Stanford identified several key parameters that control the ionic conductivity of such ions as Na⁺, Ag⁺, Cu⁺, Li⁺, K⁺, Tl⁺and NO⁺. These parameters include the ionic size, the lattice spacing (diffusion path size), the defect concentration, defect type and diffusion mechanism. Later, similar studies on the WO₃, MoO₃, TiO₂and VOPO₄materials, all of which exist in several different structures with varying molar volumes, show the criticality of matching the diffusion path size to the mobile cation. The learnings from these studies will be described.

*NBS Special Publication 364, Washington DC: U.S. Department of Commerce and National Bureau of Standards, 1972, 139-154