STUDY OF LI1+XALXTI2-X(PO4)(3) FOR LI+ POTENTIOMETRIC SENSORS

Mineral compounds LiI+xAlxTi2-x(PO4)(3) (x = 0 and x = 0.3) have been made by co-grinding and soil-gel processes. Structural characterisations by X-ray diffraction and Raman spectroscopy indicate that alumina substitution (x = 0.3) does not modify the crystallographic structure, whatever the synthesis process: compounds crystallize in the rhombohedral system with an R-3C space group. The use of the sol-gel route makes low-temperature sintering (950 degrees C) easier and moreover, lends to ceramics with a high water stability. Li1.3Al0.3Ti1-7(PO4)(3) compounds are fast ionic conductors: sigma(25 degrees C) varies from 15(-5) to 10(-4) S cm(-1), depending on the synthesis process. They have been used as ionic membranes for lithium-selective electrodes. Sensors prepared with sol-gel membranes have the best performance. the detection limit is 1.4 x 10(-4) mol dm(-3). The potassium and the protonic selectivity properties are attractive for such electrodes. For sodium, they need to be improved for biomedical applications.