Percolative ionic conduction in the LiAlSiO4glass-ceramic system

Abstract

The effect of crystallinity on the lithium ion conductivity in LiAlSi${\mathrm{O}}_4$ glass and glass-ceramic solid electrolytes has been determined. The ionic conductivity is thermally activated with an activation energy and preexponential factor that change in a marked and nonsimple manner as the volume fraction of crystallinity changes. These results are explained by using a continuum percolation model (effective medium approximation) which assumes that ionic conduction in the glass-ceramic is almost entirely within the glass phase until the crystalline volume fraction rises above ∼ 55%. The LiAlSi${\mathrm{O}}_4$ system would seem to be nearly ideal for application of percolation theory since the crystalline phase, $\beta$ eucryptite, has nearly the same composition as the glass phase. Hence, as the crystallite volume fraction increases in the glass-ceramic, the residual glass composition and conductivity remain the same. This is the first application of percolation theory to ionic transport in glass-ceramics and excellent agreement is obtained between theory and experiments for the LiAlSi${\mathrm{O}}_4$ system.