Study of Li_(1+x)Al_xTi_(2-x)(PO_4)_3 for Li~+ Potentiometric Sensors

摘要

Mineral compounds Li_(1+x)Al_xTi_(2-x)(PO_4)_3 (x = 0 and x = 0.3) have been made by co-grinding and soil-gel processes. Structural characterizations 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℃) easier and, moreover, leads to ceramics with a high water stability. Li_(1.3)Al_(0.3)Ti_(1.7)(PO_4)_3 compounds are fast ionic conductors: σ_(25℃) 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.