Interplay between the Reorientational Dynamics of the B3H8 - Anion and the Structure in KB3H8

M S Andersson; J B Grinderslev; X-M Chen; X Chen; U Häussermann; W Zhou; T R Jensen; M Karlsson; T J Udovic

doi:10.1021/acs.jpcc.0c10186

Interplay between the Reorientational Dynamics of the B₃H₈ ^- Anion and the Structure in KB₃H₈

J Phys Chem C Nanomater Interfaces. 2021 Feb 25;125(7):3716-3724. doi: 10.1021/acs.jpcc.0c10186. Epub 2021 Feb 16.

Authors

M S Andersson^{1

2}, J B Grinderslev³, X-M Chen⁴, X Chen^{4

5}, U Häussermann⁶, W Zhou², T R Jensen³, M Karlsson¹, T J Udovic^{2

7}

Affiliations

¹ Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Göteborg SE-412 96, Sweden.
² NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, United States.
³ Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, DK-8000 Aarhus, Denmark.
⁴ School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang, Henan 453007, China.
⁵ College of Chemistry and Green Catalysis Center, Zhengzhou University, Zhengzhou, Henan 450001, China.
⁶ Department of Materials and Environmental Chemistry, Stockholm University, SE-10691 Stockholm, Sweden.
⁷ Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, United States.

Abstract

The structure and reorientational dynamics of KB₃H₈ were studied by using quasielastic and inelastic neutron scattering, Raman spectroscopy, first-principles calculations, differential scanning calorimetry, and in situ synchrotron radiation powder X-ray diffraction. The results reveal the existence of a previously unknown polymorph in between the α'- and β-polymorphs. Furthermore, it was found that the [B₃H₈]^- anion undergoes different reorientational motions in the three polymorphs α, α', and β. In α-KB₃H₈, the [B₃H₈]^- anion performs 3-fold rotations in the plane created by the three boron atoms, which changes to a 2-fold rotation around the C ₂ symmetry axis of the [B₃H₈]^- anion upon transitioning to α'-KB₃H₈. After transitioning to β-KB₃H₈, the [B₃H₈]^- anion performs 4-fold rotations in the plane created by the three boron atoms, which indicates that the local structure of β-KB₃H₈ deviates from the global cubic NaCl-type structure. The results also indicate that the high reorientational mobility of the [B₃H₈]^- anion facilitates the K⁺ cation conductivity, since the 2-orders-of-magnitude increase in the anion reorientational mobility observed between 297 and 311 K coincides with a large increase in K⁺ conductivity.