Structure-Dependent Vibrational Dynamics in Mg(BH4)2 Polymorphs Probed with Neutron Vibrational Spectroscopy and First-Principles Calculations

Published

August 19, 2016

Author(s)

Mirjana NMN Dimitrievska, James L. White, Wei Zhou, Vitalie Stavila, Leonard E. Klebanoff, Terrence J. Udovic

Abstract

The structure-dependent vibrational properties of different Mg(BH₄₎d2^ polymorphs (α, β, γ and δ phases) were investigated with a combination of neutron vibrational spectroscopy measurements and density functional theory (DFT) calculations, with emphasis placed on the effects of 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 the different polymorphs. This is explained by the differences in the spatial distribution of BH₄^- anions within the various structures. These results provide fundamental insights of benefit to researchers currently studying these potentially promising hydrogen-storage materials.

Citation

Physical Chemistry Chemical Physics

Volume

18

Issue

36

Pub Type

Journals

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Keywords

Mg(BH4)2, neutron vibrational spectroscopy, DFT calculations, structural dynamics, vibrational properties

Citation

, M. , , J. , Zhou, W. , Stavila, V. , , L. and , T. (2016), Structure-Dependent Vibrational Dynamics in Mg(BH₄)₂ Polymorphs Probed with Neutron Vibrational Spectroscopy and First-Principles Calculations, Physical Chemistry Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=921232 (Accessed May 9, 2024)