Wilkening Martin, Mühle Claus, Jansen Martin, Heitjans Paul
J Phys Chem B. 2007 Aug 2;111(30):8691-4. doi: 10.1021/jp0734979. Epub 2007 Jul 11.
Li self-diffusion in rhombohedral Li7BiO6, being a promising basic material for cathodes of rechargeable ion batteries, is studied by means of 7Li stimulated echo NMR. Using the pulse sequence introduced by Jeener and Broekaert, a spin-alignment echo is created whose amplitude decay is recorded as a function of mixing time. The so-obtained two-time correlation functions follow stretched exponential behavior and lead to decay rates which can be identified directly with microscopic Li motional correlation rates (tau(-1)). Using a jump distance of about 0.2 nm, this results in a diffusion coefficient (D) of about 0.5 x 10(-16) m(2) s(-1) at 294 K. The activation energy turned out to be 0.53(3) eV which is in very good agreement with recently obtained results by means of dc-conductivity measurements probing long-range diffusion parameters. This shows that stimulated echo NMR, due to its inherent time scale, gives microscopic access to long-range transport. The prefactor tau(0)(-1) of the corresponding Arrhenius law lies in the typical range of phonon frequencies, tau(0)(-1) = 3 x 10(12) s(-1).
作为一种有前景的可充电离子电池阴极基础材料的菱面体Li7BiO6中的锂自扩散，通过7Li受激回波核磁共振进行了研究。使用Jeener和Broekaert引入的脉冲序列，产生了一个自旋排列回波，其幅度衰减作为混合时间的函数被记录下来。如此获得的二次相关函数呈现拉伸指数行为，并导致衰减率，该衰减率可直接与微观锂运动相关率（tau(-1)）确定。使用约0.2纳米的跳跃距离，这在294 K时导致约0.5×10(-16) m(2) s(-1)的扩散系数（D）。活化能结果为0.53(3) eV，这与最近通过探测长程扩散参数的直流电导率测量获得的结果非常吻合。这表明，由于其固有的时间尺度，受激回波核磁共振能够从微观角度研究长程传输。相应阿仑尼乌斯定律的前置因子tau(0)(-1)处于声子频率的典型范围内，tau(0)(-1) = 3×10(12) s(-1)。
