Neutron Scattering Investigations of the Global and Local Structures of Ammine Yttrium Borohydrides

Published

July 22, 2021

Author(s)

Jakob Grinderslev, Mikael S. Andersson, Benjamin Trump, Wei Zhou, Terrence J. Udovic, Maths Karlsson, Torben Jensen

Abstract

Complex metal hydrides are a fascinating and continuously expanding class of materials with many properties relevant for solid-state hydrogen and ammonia storage and solid state electrolytes. The crystal structures are often investigated using powder X-ray diffraction (PXD), which can be ambiguous. Here we revisit the crystal structure of Y(¹¹BD₄)₃∙3ND₃ with the use of neutron diffraction, which, in comparison to previous PXD studies, provides accurate information about the D positions in the compound. Upon cooling to 10 K, the compound underwent a polymorphic transition, and a new monoclinic low-temperature polymorph denoted as α-Y(¹¹BD₄)₃∙3ND₃ was discovered. Furthermore, the series of Y(¹¹BH₄)₃∙xNH₃ (x = 0, 3 and 7) were also investigated with inelastic neutron scattering and infrared spectroscopy techniques, which provided information of the local coordination environment of the ¹¹BH₄- and NH₃ groups as well as unique insight into the hydrogen dynamics. Partial deuteration using ND₃ in Y(¹¹BH₄)₃∙xND₃ (x = 3 and 7) allowed for an unambiguous assignment of the vibrational bands corresponding to the NH₃ and ¹¹BH₄- in Y(¹¹BH₄)₃∙xNH₃, due to the much larger neutron scattering cross section of H compared to D. The vibrational spectra of Y(¹¹BH₄)₃∙xNH₃ could roughly be divided into three regions: i) below 55 meV, containing mainly ¹¹BH₄- librational motions, ii) 55 - 130 meV, containing mainly NH₃ librational motions and iii) above 130 meV, containing ¹¹B-H and N-H bending and stretching motions.

Citation

Journal of Physical Chemistry C

Volume

125

Issue

28

Pub Type

Journals

Keywords

ammine yttrium borohydrides, crystal structures, inelastic neutron scattering, neutron powder diffraction, neutron vibrational spectroscopy, x-ray diffraction, Y(BH4)3, yttrium borohydride

Citation

Grinderslev, J. , Andersson, M. , Trump, B. , Zhou, W. , Udovic, T. , Karlsson, M. and Jensen, T. (2021), Neutron Scattering Investigations of the Global and Local Structures of Ammine Yttrium Borohydrides, Journal of Physical Chemistry C (Accessed April 25, 2024)