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

作者：Skripov Alexander V^*; Skoryunov Roman V; Soloninin Alexei V; Babanova Olga A; Tang Wan Si; Stavila Vitalie; Udovic Terrence J

来源：Journal of Physical Chemistry C, 2015, 119(48): 26912-26918.

DOI：10.1021/acs.jpcc.5b10055

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 H-1, Li-7, and Na-23 NMR spectra and spin-lattice 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](-) anions. The results of our Li-7 and Na-23 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.

• 出版日期2015-12-3