LITHIUM ALUMINATE-DOPED LITHIUM ORTHOSILICATE - SOL-GEL CERAMICS AND LITHIUM DYNAMICS

Dense ceramics (Li4+xSi1-xAlxO4 with 0 ≤ x ≤ 0.3) are obtained by sintering at 700-900°C, without prior calcination, of sol-gel powders prepared by an alkoxide-hydroxide route. In comparison with the pure lithium orthosilicate (3 × 10-4 S · cm-1 at 350°C), only a slight enhancement of the ionic conductivity is noted for monophase ceramics with Li4SiO4-type structure (5 × 10-4 S · cm-1 at 350°C for x = 0.3). Higher conductivity (2 × 10-2 S · cm-1 at 350°C) is observed for an heterogeneous material formed of a lithium silicoaluminate phase (x = 0.2) with the Li4SiO4-type structure coexisting with lithium hydroxide. In this two-phase material, ac conductivity and 7Li spin-lattice relaxation data are consistent with the formation of a new kinetic path, via a thin layer along the interface, which enhances the lithium mobility. © 1991.