THE EFFECT OF PRECURSORS ON THE IONIC-CONDUCTIVITY IN LITHIUM SILICATE GELS

ac impedance measurements were carried out on lithium silicate gels prepared in four different ways. The first two referred to as polymerized gels are prepared by hydrolysis of tetraethylorthosilicate (TEOS) with either a methanol-water-LiNO3 solution, or a methanol-LiOH solution. The second two referred to as infiltrated gels are prepared by soaking previously formed colloidal silica gels in either LiNO3 or LiOH solutions. The ionic conductivity results indicate different conducting mechanisms in the gels prepared with LiNO3 versus those with LiOH. In the LiNO3 gels, the conductivity mechanism is associated with the xerogel/crystalline-LiNO3 composite, while in the LiOH gels the lithium is found to be associated with non-bridging oxygens. Furthermore, the conductivity in the LiNO3 gels is higher in the cooling cycle than in the heating cycle, corresponding to a supercooling of the LiNO3 melt below its crystallization temperature of 254-degrees-C. In general, polymerized gels have higher conductivities than infiltrated gels.