Journal
JOURNAL OF ALLOYS AND COMPOUNDS
Volume 636, Issue -, Pages 293-297Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2015.02.194
Keywords
Energy storage materials; Diffusion; Nuclear resonances
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Funding
- Russian Foundation for Basic Research [15-03-01114]
- U.S. Civilian Research & Development Foundation [RUP1-7076-EK12]
- DOE EERE [DE-EE0002978]
- National Science Foundation [OISE-9531011]
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To study the effects of partial halide anion substitution on the reorientational motion of [BH4] anions in NaBH4, we have measured the H-1 and B-11 NMR spectra and spin-lattice relaxation rates in the cubic solid solutions Na(BH4)(0.5)Cl-0.5 and Na(BH4)(0.5)I-0.5 over broad ranges of temperature (8-324 K) and the resonance frequency (14-90 MHz). For both solid solutions, the measured H-1 spin-lattice relaxation rates are governed by reorientations of BH4 groups, and the experimental data can be satisfactorily described by the model with a Gaussian distribution of the activation energies. The average values of the activation energies derived from the H-1 spin-lattice relaxation data are 192 +/- 7 meV for Na(BH4)(0.5)Cl-0.5 and 120 +/- 3 meV for Na(BH4)0.5I0.5. At a given temperature, the reorientational jump rates are found to increase in the order of Na(BH4)(0.5)Cl-0.5-NaBH4-Na(BH4)(0.5)I-0.5, in agreement with the quasielastic neutron scattering (QENS) results. This trend correlates with the lattice expansion reflecting the increase in the size of the corresponding anions (in the order of Cl -[BH4] -I). (C) 2015 Elsevier B.V. All rights reserved.
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