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Vibrational properties of β‐KSiH 3 and β‐RbSiH 3 : a combined Raman and inelastic neutron scattering study
Author(s) -
Mink Janos,
Lin YuanChih,
Karlsson Maths,
Österberg Carin,
Udovic Terrence J.,
Fahlquist Henrik,
Häussermann Ulrich
Publication year - 2017
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5013
Subject(s) - libration (molecule) , raman spectroscopy , anharmonicity , inelastic neutron scattering , chemistry , inelastic scattering , raman scattering , atmospheric temperature range , molecular vibration , oxonium ion , ion , neutron scattering , proton , analytical chemistry (journal) , atomic physics , scattering , condensed matter physics , physics , thermodynamics , optics , quantum mechanics , geometry , point (geometry) , mathematics , organic chemistry , chromatography
The hydrogen storage materials A SiH 3 ( A = K and Rb) represent complex metal hydrides built from metal cations and pyramidal SiH 3 − ions. At room temperature, SiH 3 − moieties are randomly oriented because of dynamical disorder (α‐modifications). At temperatures below 200 K, A SiH 3 exist as ordered low‐temperature (β) modifications. The vibrational properties of β‐ A SiH 3 were characterized by a combination of Raman spectroscopy and inelastic neutron scattering. Internal modes of SiH 3 − are observed in the spectral range 1800–1900 cm −1 (stretching modes) and 890–1000 cm −1 (bending modes). External modes are observed below 500 cm −1 . Specifically, SiH 3 − librations are between 300–450 cm −1 and 270–400 cm −1 for A = K and Rb, respectively, SiH 3 − translations are between 95 and 160 cm −1 , K + translations are in the range 60–100 cm −1 and Rb + translations in the range 50–70 cm −1 . The red‐shift of libration modes for A = Rb is associated with a 15–30% reduction of the libration force constants of SiH 3 − ions in β‐RbSiH 3 . This correlates with a lower temperature for the β–α order–disorder phase transition (278 vs 298 K). Libration modes become significantly anharmonic with increasing temperature but are maintained up to at least 200 K. The vibrational properties of A SiH 3 compare well to those of alkali metal borohydrides A BH 4 ( A = Na–Cs). Copyright © 2016 John Wiley & Sons, Ltd.