IONIC-CONDUCTIVITY IN THE H2O-P2O5-SIO2, LI2O-P2O5-SIO2, NA2O-P2O5-SIO2, K2O-P2O5-SIO2 SYSTEM PREPARED BY SOL-GEL METHODS

Glasses in the M2O-P2O5-SiO2 system (M=H, Li, Na, K) were prepared by slowly heating the corresponding sol-gels. Sol-gels were prepared from tetraethylorthosilicate and inorganic reagents. Monolithic samples are obtained when the silica content is greater than 60 mole%. Ionic conductivity was measured by the complex impedance method. For samples of the composition 0.07M2O-0.20P2O5-0.73SiO2 (M=Li, Na, K) it was found that σK+≥σNa+≥σLi+. FTIR data indicate that the gels are phase separated into phosphate rich and silicate rich regions. This is confirmed by EDX. The alkali cations are shown to be located in the phosphate rich regions. Samples prepared by immersing P2O5-SiO2 binary monoliths in molten LiCl and allowing to equilibrate under ambient conditions indicate relatively high water content. The highest value of the ionic conductivity measured was 5×10-2 (ω cm)-1 at 323 K for the composition 0.09P2O5-0.41SiO2-0.33LiCl-0.17H2O is attributed to proton motion. © 1990.