Vibrational properties of β-KSiH3 and β-RbSiH3: A combined Raman and inelastic neutron scattering study

J. Mink, Yuan Chih Lin, Maths Karlsson, Carin Österberg, Terrence J. Udovic, Henrik Fahlquist, Ulrich Häussermann

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The hydrogen storage materials ASiH3 (A=K and Rb) represent complex metal hydrides built from metal cations and pyramidal SiH3 - ions. At room temperature, SiH3 - moieties are randomly oriented because of dynamical disorder (α-modifications). At temperatures below 200K, ASiH3 exist as ordered low-temperature (β) modifications. The vibrational properties of β-ASiH3 were characterized by a combination of Raman spectroscopy and inelastic neutron scattering. Internal modes of SiH3 - are observed in the spectral range 1800-1900cm-1 (stretching modes) and 890-1000cm-1 (bending modes). External modes are observed below 500cm-1. Specifically, SiH3 - librations are between 300-450cm-1 and 270-400cm-1 for A=K and Rb, respectively, SiH3 - translations are between 95 and 160cm-1, K+ translations are in the range 60-100cm-1 and Rb+ translations in the range 50-70cm-1. The red-shift of libration modes for A=Rb is associated with a 15-30% reduction of the libration force constants of SiH3 - ions in β-RbSiH3. This correlates with a lower temperature for the β-α order-disorder phase transition (278 vs 298K). Libration modes become significantly anharmonic with increasing temperature but are maintained up to at least 200K. The vibrational properties of ASiH3 compare well to those of alkali metal borohydrides ABH4 (A=Na-Cs).

Original languageEnglish
JournalJournal of Raman Spectroscopy
DOIs
Publication statusAccepted/In press - 2016

Keywords

  • Alkali metal silanides
  • Complex metal hydrides
  • Inelastic neutron scattering
  • Libration modes
  • Order-disorder phase transition

ASJC Scopus subject areas

  • Materials Science(all)
  • Spectroscopy

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    Mink, J., Lin, Y. C., Karlsson, M., Österberg, C., Udovic, T. J., Fahlquist, H., & Häussermann, U. (Accepted/In press). Vibrational properties of β-KSiH3 and β-RbSiH3: A combined Raman and inelastic neutron scattering study. Journal of Raman Spectroscopy. https://doi.org/10.1002/jrs.5013