5 years ago

Reorientational Hydrogen Dynamics in Complex Hydrides with Enhanced Li+ Conduction

Reorientational Hydrogen Dynamics in Complex Hydrides with Enhanced Li+ Conduction
Bernhard Frick, Yigang Yan, Léo Duchêne, Hans Hagemann, Arndt Remhof, Ruben-Simon Kühnel, Zbigniew Łodziana, Tatsiana Burankova, Jan P. Embs
Lithium amide–borohydrides Li[BH4]1–x[NH2]x possess liquid-like Li superionic conductivity at nearly ambient temperature. The fast Li+ diffusion facilitated by the localized motions of the anions is proposed to occur through a network of vacant tetrahedral sites, acting as conduction channels. To study the reorientational dynamics of the anions, we have performed quasielastic neutron scattering experiments on samples with different compositions (x = 2/3, 0.722, 0.737, 3/4) over a broad temperature and time range. To unambiguously disentangle the contributions of the two species, [BH4] and [NH2], we took advantage of deuterium labeling and could clearly demonstrate that the quasielastic broadening is mainly determined by the [BH4] reorientations. With the help of a newly developed model, supported by ab initio molecular dynamics calculations, we have identified three relaxation components, which account for generally anisotropic C3-rotations of the [BH4] tetrahedra including jumps by a small angle from the equilibrium position.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b05651

DOI: 10.1021/acs.jpcc.7b05651

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