Pecularity of lithium electrodiffusion into fulleride single crystals

Diffusion of lithium cations in C₆₀ single crystals driven by an electric field has been studied. It was found that the stoichiometry of C₆₀ single crystals can be changed with respect to lithium by injection of Li⁺ ions through the heterojunction Li₇SiPO₈|C₆₀ and electrons through the heterojunction C₆₀| Graphite. The double charge injection changes the stoichiometry of lithium in a C₆₀ single crystal and increases both the lithium ionic and electronic conductivity. The electronic conductivity in Li_xC₆₀ crystals is non-metallic in nature. The temperature dependence of the electronic conductivity lithium doped C₆₀ single crystals was investigated. It was found that electrons occupied the lowest singlet exited states (LUMO) and that this leads to the appearance of an intensive EPR signal. The temperature dependence of the concentration of paramagnetic centers was investigated. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.