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Title: Structure-dependent vibrational dynamics of Mg(BH 4 ) 2 polymorphs probed with neutron vibrational spectroscopy and first-principles calculations

Journal Article · · Physical Chemistry Chemical Physics. PCCP
DOI:https://doi.org/10.1039/C6CP04469G· OSTI ID:1325623
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The structure-dependent vibrational properties of different Mg(BH4)2 polymorphs (..alpha.., ..beta.., ..gamma.., and ..delta.. phases) were investigated with a combination of neutron vibrational spectroscopy (NVS) measurements and density functional theory (DFT) calculations, with emphasis placed on the effects of the local structure and orientation of the BH4- anions. DFT simulations closely match the neutron vibrational spectra. The main bands in the low-energy region (20-80 meV) are associated with the BH4- librational modes. The features in the intermediate energy region (80-120 meV) are attributed to overtones and combination bands arising from the lower-energy modes. The features in the high-energy region (120-200 meV) correspond to the BH4- symmetric and asymmetric bending vibrations, of which four peaks located at 140, 142, 160, and 172 meV are especially intense. There are noticeable intensity distribution variations in the vibrational bands for different polymorphs. This is explained by the differences in the spatial distribution of BH4- anions within various structures. An example of the possible identification of products after the hydrogenation of MgB2, using NVS measurements, is presented. These results provide fundamental insights of benefit to researchers currently studying these promising hydrogen-storage materials.

Research Organization:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Fuel Cell Technologies Office
DOE Contract Number:
AC36-08GO28308
OSTI ID:
1325623
Report Number(s):
NREL/JA-5900-67131
Journal Information:
Physical Chemistry Chemical Physics. PCCP, Vol. 18, Issue 36; ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English

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Cited By (3)

In‐Situ/Operando X‐ray Characterization of Metal Hydrides journal March 2019
Structural and reorientational dynamics of tetrahydroborate (BH 4 − ) and tetrahydrofuran (THF) in a Mg(BH 4 ) 2 ·3THF adduct: neutron-scattering characterization journal January 2020
Hydrogen Desorption in Mg(BH4)2-Ca(BH4)2 System journal August 2019

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Related Subjects

36 MATERIALS SCIENCE
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
polymorphs
vibrational properties
neutron vibrational spectroscopy
NVS
density functional theory
DFT