Nuclear Magnetic Resonance Studies of Reorientational Motion and Li Diffusion in LiBH4-LiI Solid Solutions

作者：Skripov Alexander V^*; Soloninin Alexei V; Rude Line H; Jensen Torben R; Filinchuk Yaroslav

来源：Journal of Physical Chemistry C, 2012, 116(50): 26177-26184.

DOI：10.1021/jp3080892

To study the reorientational motion of the BH4 groups and the translational diffusion of Li+ ions in LiBH4-LiI solid solutions with 2:1, 1:1, and 1:2 molar ratios, we have measured the H-1, B-11, and Li-7 NMR spectra and spin-lattice relaxation rates in these compounds over the temperature range 18-520 K. It is found that, at low temperatures, the reorientational motion of the BH4 groups in LiBH4-LiI solid solutions is considerably faster than in all other borohydride-based systems studied so far. Our results are consistent with a coexistence of at least two types of reorientational processes with different characteristic rates. For the faster reorientational process, the average activation energies derived from our data are 53 +/- 4, 39 +/- 4, and 33 +/- 4 meV for the LiBH4-LiI solid solutions with 2:1, 1:1, and 1:2 molar ratios, respectively. In the studied range of iodine concentrations, the Li+ jump rates are found to decrease with increasing I- content. The activation energies for Li diffusion obtained from our data are 0.63 +/- 0.01, 0.65 +/- 0.01, and 0.68 +/- 0.01 eV for the samples with 2:1, 1:1, and 1:2 molar ratios, respectively.

• 出版日期2012-12-20