Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy |
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Authors: | Michael R Hartman John J Rush Robert C Bowman Jr |
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Institution: | a NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-8562, USA b Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA c Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA |
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Abstract: | The crystalline structure of a 7Li and 11B labeled lithium borohydride has been investigated using neutron powder diffraction at 3.5, 360, and 400 K. The B-H bond lengths and H-B-H angles for the BH4]− tetrahedra indicated that the tetrahedra maintained a nearly ideal configuration throughout the temperature range investigated. The atomic displacement parameters at 360 K suggest that the BH4]− tetrahedra become increasingly disordered as a result of large amplitude librational and reorientational motions as the orthorhombic to hexagonal phase transition (T=384 K) is approached. In the high-temperature hexagonal phase, the BH4]− tetrahedra displayed extreme disorder about the trigonal axis along which they are aligned. Neutron vibrational spectroscopy data were collected at 5 K over an energy range of 10-170 meV, and were found to be in good agreement with prior Raman and low-resolution neutron spectroscopy studies. |
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Keywords: | Neutron scattering Lithium borohydride NMR Hydrogen storage |
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