Molecular and Ionic Dynamics in NaxLi6−xC60

We report on the C60, Na, and Li dynamics in NaxLi6−xC60 fullerides (x = 0, 1, 5, and 6) in the temperature range  80−550 K by using 13C, 23Na, and 7Li solid state NMR. The results show that the C60 reorientation dynamics is hindered at room temperature for the Li-enriched fullerides, but it is active for the Na rich ones with a rate of the order of few kilohertz. 23Na and 7Li NMR measurements show the presence of two dominant thermally activated dynamics that can be associated with Li/Na ionic motions within the octahedral sites (intrasite motion) and between the octahedral and tetrahedral sites (intersite motion). The substitution of one Na or one Li ion in the end members Li6C60 and Na6C60, respectively, yields to an increase of the hopping rate of the intersite motion, which is necessary for the ionic diffusion in possible fulleride-based ionic conductors.

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