NASICON-type compounds, Li1+xAlxA2-x(PO4)3, in these systems were fabricated by using sol-gel and co-grinding processes, and the structural and electrical characteristics of pellet samples were examined. Solid solutions were obtained which had x-values ranging from 0 to 0.6. A minimum in the rhombohedral c-parameter occurred at an x-value of about 0.1, for both materials. The grain ionic conductivity was characterized only in the case of the Ge-based compounds. It was related to the carrier concentration and the structural properties of the NASICON covalent skeleton. The results confirmed that the Ti-based framework was more conducive to Li migration than was the Ge-based one. A grain conductivity of 10-3S/cm was found at 25C in the case of Li1.3Al0.3Ti1.7(PO4)3. A total conductivity of about 6 x 10-5S/cm was found for sintered pellets, because of grain-boundary effects. The use of such ceramics in ionosensitive selective electrode devices showed that the most confined unit cell (as in Ge-based materials) was more advantageous for selectivity, although it was less conductive.

Comparative Study of Lithium Ion Conductors in the System, Li(Al,A)2(PO4)3. M.Cretin, P.Fabry: Journal of the European Ceramic Society, 1999, 19[16], 2931-40