STRUCTURAL AND LITHIUM ION-TRANSPORT STUDIES IN SOL-GEL-PREPARED LITHIUM SILICOPHOSPHATE GLASSES

Lithium silicophosphate glasses have been prepared by a sol-gel route over a wide range of compositions. Their structural and electrical pro perties have been investigated. Infrared spectroscopic studies show th e presence of hydroxyl groups attached to Si and P. MAS NMR investigat ions provide evidence for the presence of different phosphatic units i n the structure. The variations of de conductivities at 423 K and acti vation energies have been studied as a function of composition, and bo th exhibit an increasing trend with the ratio of nonbridging oxygen to bridging oxygen in the structure. Ac conductivity behavior shows that the power law exponent, s, is temperature dependent and exhibits a mi nimum. Relaxation behavior has been examined in detail using an electr ical modulus formalism, and modulus data were fitted to Kohlraush-Will iam-Watts stretched exponential function. A structural model has been proposed and the unusual properties exhibited by this unique system of glasses have been rationalized using this model. Ion transport in the se glasses appears to be confined to unidimensional conduits defined b y modified phosphate chains and interspersed with unmodified silica un its.