Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku Sendai 980-8577, Japan.
J Chem Phys. 2014 Mar 28;140(12):124509. doi: 10.1063/1.4869347.
The lithium ion diffusion coefficient of a 93% Li β-alumina single crystal was measured for the first time using pulsed field gradient (PFG) NMR spectroscopy with two different crystal orientations. The diffusion coefficient was found to be 1.2 × 10(-11) m(2)/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10(-13) m(2)/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the β-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297-333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li β-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li β-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li β-alumina system.
首次使用脉冲梯度（PFG）NMR 光谱法，通过两种不同的晶体取向，测量了 93% Liβ-氧化铝单晶体的锂离子扩散系数。在室温下，垂直于 c 轴方向的扩散系数为 1.2×10(-11) m(2)/s。沿 c 轴方向的 Li 离子扩散系数非常小（333 K 时为 6.4×10(-13) m(2)/s），这表明 Li 离子在β-氧化铝晶体中的宏观扩散主要是二维的。还使用 NMR 线宽减小数据和阻抗测量来估计相同样品的扩散系数。阻抗数据与 PFG-NMR 数据吻合较好，而线宽减小测量则提供了较低的扩散系数。线宽减小测量还提供了相对较低的扩散系数活化能和指数前因子。通过 PFG-NMR 在 297-333 K 的温度范围内获得了温度相关的扩散系数，由此估算了 Li 离子扩散的活化能。通过 PFG-NMR 获得的活化能小于通过阻抗测量获得的活化能，这表明 93% Liβ-氧化铝单晶体存在热激活缺陷形成能。通过 PFG-NMR 实验观察到了 93% Liβ-氧化铝单晶体中 Li 离子的扩散系数随扩散时间的变化。Li 离子在分形维度上的运动可能是解释 93% Liβ-氧化铝体系中观察到的扩散系数随扩散时间变化的一种可能解释。
