The Li diffusion and transport parameters of binary lithium carbide Li2C2 were complementarily investigated by 7Li nuclear magnetic resonance and impedance spectroscopy. Long-range Li diffusion parameters were measured by using mixing-time-dependent and temperature-variable stimulated echo nuclear magnetic resonance spectroscopy. The method was sensitive to ultra-slow Li hopping processes which were probed from an atomic-scale point of view. Two-time phase correlation functions S2 obtained could be parameterized by stretched exponentials only. The corresponding echo decay rates τ−1, which were recorded at a resonance frequency of e.g. 155.5MHz, showed Arrhenius behaviour revealing an activation energy of 0.80eV. This value was in very good agreement with that deduced from dc conductivity measurements (0.79eV) probing Li transport processes on a macroscopic length scale. The comparison of impedance data with the measured nuclear magnetic resonance echo decay functions showed that both methods reflect diffusion processes being characterized by very similar motional correlation functions.

Ultra-Slow Li Ion Dynamics in Li2C2 - on the Similarities of Results from 7Li Spin-Alignment Echo NMR and Impedance Spectroscopy. B.Ruprecht, H.Billetter, U.Ruschewitz, M.Wilkening: Journal of Physics - Condensed Matter, 2010, 22[24], 245901