Anion Reorientations and Cation Diffusion in LiCB11H12 and NaCB11H12: 1H, 7Li, and 23Na NMR Studies

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• 作者：Alexander V. Skripov ; Roman V. Skoryunov ; Alexei V. Soloninin ; Olga A. Babanova ; Wan Si Tang ; Vitalie Stavila ; Terrence J. Udovic
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：December 3, 2015
• 年：2015
• 卷：119
• 期：48
• 页码：26912-26918
• 全文大小：326K
• ISSN：1932-7455

文摘

To study the dynamical properties of the monocarba-closo-dodecaborates LiCB₁₁H₁₂ and NaCB₁₁H₁₂ showing the exceptionally high ionic conductivities in the high-temperature disordered phases, we have measured the temperature dependences of the ¹H, ⁷Li, and ²³Na NMR spectra and spin鈥搇attice relaxation rates in these compounds below and above the phase transition points. It has been found that for both compounds the transition from the low-T ordered to the high-T disordered phase (near 384 and 376 K for LiCB₁₁H₁₂ and NaCB₁₁H₁₂, respectively) is accompanied by a nearly 3 orders of magnitude increase in the reorientational jump rate of [CB₁₁H₁₂]^{鈭?/sup> anions. The results of our 7Li and 23Na NMR measurements indicate that the phase transitions from the low-T to the high-T phases of both LiCB₁₁H₁₂ and NaCB₁₁H₁₂ are also accompanied by a strong acceleration of translational diffusion of cations (Li+ or Na+). In the high-T phases of LiCB₁₁H₁₂ and NaCB₁₁H₁₂, the cation diffusion is characterized by low activation energies: 92 (7) and 152 (8) meV, respectively. These results are consistent with the high superionic conductivity in the disordered phases of LiCB₁₁H₁₂ and NaCB₁₁H₁₂; furthermore, they suggest that the enhanced reorientational mobility of large nearly spherical anions may facilitate the translational mobility of the cations.}