Comparative study of lithium ion conductors in the system Li(1-x)Al(x)A(2-x)(IV) (PO4)(3) with A(IV) = Ti or Ge and 0 <= x <= 0.7 for use as Li+ sensitive membranes

Preparations and physico-chemical characterizations of NASICON-type compoun ds in the system Li1+x Al(x)A(2-x)(IV)(PO4)(3) (A(IV)= Ti Or Ge) are descri bed. Ceramics have been fabricated by sol-gel and co-grinding processes for use as ionosensitive membrane for Li+ selective electrodes. The structural and electrical characteristics of the pellets have been examined. Solid so lutions are obtained with Al/Ti and Al/Ge substitutions in the range 0 less than or equal to x less than or equal to 0.6. A minimum of the rhombohedra l c parameter appears for x about 0.1 for both solutions. The grain ionic c onductivity has been characterized only in the case of Ge-based compounds. It is related to the carrier concentration and the structural properties of the NASICON covalent skeleton. The results confirm that the Ti-based frame work is more calibrated to Li+ migration than the Ge-based one. A grain con ductivity of 10(-3) S cm(-1) is obtained at 25 degrees C in the case of Li1 .3Al0.3Ti1.7(PO4)(3) A total conductivity of about 6x10(-5) S cm(-1) is mea sured on sintered pellets because of grain boundary effects. The use of suc h ceramics in ISE devices has shown that the most confined unit cell (i.e. in Ge-based materials) is more appropriate for selectivity effect, although it is less conductive. (C) 1999 Elsevier Science Ltd. All rights reserved.