TY - JOUR
T1 - Nuclear magnetic resonance study of atomic motion in the mixed borohydride-amide Li2(BH4) (NH2)
AU - Skoryunov, R. V.
AU - Babanova, O. A.
AU - Soloninin, A. V.
AU - Skripov, A. V.
AU - Orimo, S.
N1 - Funding Information:
This work was supported by the Russian Science Foundation (Grant No. 19-12-00009 ) and by JSPS KAKENHI (Grant No. JP18H05513 ). Appendix A
Funding Information:
This work was supported by the Russian Science Foundation (Grant No. 19-12-00009) and by JSPS KAKENHI (Grant No. JP18H05513).
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/5/15
Y1 - 2020/5/15
N2 - In order to study the reorientational motion of the anions and the translational diffusion of Li+ cations in the borohydride-amide Li2(BH4) (NH2) showing fast-ion conduction, we have measured the 1H, 7Li, and 11B NMR spectra and spin-lattice relaxation rates over the temperature range of 80–341 K. Our measurements have revealed a coexistence of several motional processes in this mixed-anion compound. The fastest processes correspond to two thermally-activated types of BH4 reorientations. These reorientations give rise to two peaks of the 1H, 7Li, and 11B spin-lattice relaxation rates observed near 220 K and 290 K; they are characterized by the activation energies of 196 (2) meV and 498 (5) meV, respectively. For each of the two processes, the reorientational jump rate reaches ∼108 s−1 near the corresponding peak temperature. The diffusive jump motion of Li+ ions is found to be much slower than both reorientational processes; it leads to the 7Li NMR line narrowing above 300 K that indicates the onset of Li+ jumps at the frequency scale of ∼104 s−1. As the temperature approaches the melting point of Li2(BH4) (NH2), Tm ≈ 365 K, we have also observed the onset of diffusive motion of H-containing species at the same frequency scale.
AB - In order to study the reorientational motion of the anions and the translational diffusion of Li+ cations in the borohydride-amide Li2(BH4) (NH2) showing fast-ion conduction, we have measured the 1H, 7Li, and 11B NMR spectra and spin-lattice relaxation rates over the temperature range of 80–341 K. Our measurements have revealed a coexistence of several motional processes in this mixed-anion compound. The fastest processes correspond to two thermally-activated types of BH4 reorientations. These reorientations give rise to two peaks of the 1H, 7Li, and 11B spin-lattice relaxation rates observed near 220 K and 290 K; they are characterized by the activation energies of 196 (2) meV and 498 (5) meV, respectively. For each of the two processes, the reorientational jump rate reaches ∼108 s−1 near the corresponding peak temperature. The diffusive jump motion of Li+ ions is found to be much slower than both reorientational processes; it leads to the 7Li NMR line narrowing above 300 K that indicates the onset of Li+ jumps at the frequency scale of ∼104 s−1. As the temperature approaches the melting point of Li2(BH4) (NH2), Tm ≈ 365 K, we have also observed the onset of diffusive motion of H-containing species at the same frequency scale.
KW - A. Energy storage materials
KW - C. Diffusion
KW - D. Nuclear resonances
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U2 - 10.1016/j.jallcom.2020.153821
DO - 10.1016/j.jallcom.2020.153821
M3 - Article
AN - SCOPUS:85077933850
VL - 823
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
SN - 0925-8388
M1 - 153821
ER -