Institute of Physical Chemistry and Electrochemistry, Leibniz University Hannover, Callinstraße 3a, D-30167 Hannover, Germany.
J Phys Condens Matter. 2010 Jun 23;22(24):245901. doi: 10.1088/0953-8984/22/24/245901. Epub 2010 May 26.
Li diffusion and transport parameters of binary lithium carbide Li(2)C(2) were complementarily investigated by (7)Li (nuclear magnetic resonance) NMR and impedance spectroscopy. Long-range Li diffusion parameters were measured by using mixing-time-dependent and temperature-variable stimulated echo NMR spectroscopy. The method is sensitive to ultra-slow Li hopping processes which were probed from an atomic-scale point of view. Two-time phase correlation functions S(2) obtained can be parameterized by stretched exponentials only. The corresponding echo decay rates τ(-1), which were recorded at a resonance frequency of e.g. 155.5 MHz, show Arrhenius behaviour revealing an activation energy of 0.80(2) eV. This value is in very good agreement with that deduced from dc conductivity measurements (0.79(2) eV) probing Li transport processes on a macroscopic length scale. The comparison of impedance data with the measured NMR echo decay functions showed that both methods reflect diffusion processes being characterized by very similar motional correlation functions.
采用（7）Li（核磁共振）NMR 和阻抗谱法对二元碳化锂 Li（2）C（2）的 Li 扩散和输运参数进行了补充研究。通过使用混合时间相关和温度变化的受激回波 NMR 光谱法测量长程 Li 扩散参数。该方法对超慢 Li 跳跃过程非常敏感，可以从原子尺度的角度探测到这些过程。仅通过拉伸指数对获得的两个时间相位相关函数 S（2）进行参数化。在例如 155.5 MHz 的共振频率下记录的相应回波衰减率 τ（-1）表现出 Arrhenius 行为，揭示出 0.80（2）eV 的活化能。该值与通过直流电导率测量（0.79（2）eV）推断的结果非常吻合，后者探测宏观长度尺度上的 Li 输运过程。将阻抗数据与测量的 NMR 回波衰减函数进行比较表明，两种方法都反映了由非常相似的运动相关函数表征的扩散过程。
