Vibrational Properties of β-KSiH3 and β-RbSiH3: A Combined Raman and Inelastic Neutron Scattering Study

Published

February 1, 2017

Author(s)

Janos Mink, Yuan-Chih Lin, Maths Karlsson, Carin Osterberg, Terrence J. Udovic, Henrik Fahlquist, Ulrich Haussermann

Abstract

The hydrogen storage materials ASiH₃ (A=K, 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 200 K, ASiH₃ exist as ordered low-temperature β modifications. The vibrational properties of βASiH₃ were characterized by a combination of Raman spectroscopy and inelastic neutron scattering. Internal modes of SiH₃- 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, SiH₃- librations are between 300 and 450 cm^-1 and 270 and 400 cm^-1 for A = K and Rb, respectively, SiH₃- translations are between 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 SiH₃- ions in β-RbSiH₃. This correlates with a lower temperature for the α-β order-disorder phase transition (273 K vs 298 K). Libration modes become significantly anharmonic with increasing temperature but are maintained up to at least 200 K.

Citation

Journal of Raman Spectroscopy

Volume

48

Issue

2

Pub Type

Journals

Download Paper

Local Download

Keywords

inelastic neutron scattering, KSiH3, neutron vibrational spectroscopy, phonons, Raman spectroscopy, RbSiH3, silanides, vibrational density of states

Citation

Mink, J. , Lin, Y. , Karlsson, M. , Osterberg, C. , Udovic, T. , Fahlquist, H. and Haussermann, U. (2017), Vibrational Properties of β-KSiH₃ and β-RbSiH₃: A Combined Raman and Inelastic Neutron Scattering Study, Journal of Raman Spectroscopy, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=921359 (Accessed January 2, 2025)