Quasielastic Neutron Scattering Study of Tetrahydroborate Anion Dynamical Perturbations in Sodium Borohydride due to Partial Halide Anion Substitution

Published

October 5, 2015

Author(s)

Kristina Verdal, Terrence J. Udovic, John J. Rush, Alexander V. Skripov

Abstract

Equimolar NaBh₄-NaX (X=cl and l) solid solutions were synthesized to study, via quasielastic neutron scattering, the effect of partial halide anion substitution on the reorientational dynamics of tetrahydroborate (BH₄-) anions in NaBH₄. The BH₄- reorientational mobility increased in the order of NaBH₄-NaCl, NaBH₄, and NaBH₄-Nal, which corresponded with expanding face-centered-cubic lattices accommodating the respective increasing sizes of the Cl, BH₄ nad I anions. The BH₄ anions in NaBH₄-NaCl were found (at least above 400 K) to undergo 'cubic' tumbling motions with the four H atoms per anion visiting all eight corners of a cube, similar to what was previously observed for NaBH₄. In contrast, the BH₄ anions in NaBH₄-Nal were found to undergo something more akin to 'tetrahedral' tumbling motions, where the H atoms visit all four corners of a tetrahedron. Despite a noticeable softening of the BH₄ torsional energies with increasing lattice constant amongst NaBH₄ and the two solid solutions, all three compounds exhibited similar activation energies for reorientation of about 11-12 kJ mol^-1.

Citation

Journal of Alloys and Compounds

Volume

645

Pub Type

Journals

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Keywords

dynamics, neutron scattering, quasielastic neutron scattering, neutron vibrational spectroscopy, reorientational mobility, sodium borohydride, sodium chloride, sodium iodide, tetrahydroborate

Citation

Verdal, K. , Udovic, T. , Rush, J. and Skripov, A. (2015), Quasielastic Neutron Scattering Study of Tetrahydroborate Anion Dynamical Perturbations in Sodium Borohydride due to Partial Halide Anion Substitution, Journal of Alloys and Compounds, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=917131 (Accessed July 17, 2024)