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



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


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.
Journal of Raman Spectroscopy


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


Mink, J. , Lin, Y. , Karlsson, M. , Osterberg, C. , Udovic, T. , Fahlquist, H. and Haussermann, U. (2017), Vibrational Properties of &#946;-KSiH<sub>3</sub> and &#946;-RbSiH<sub>3</sub>: A Combined Raman and Inelastic Neutron Scattering Study, Journal of Raman Spectroscopy, [online], (Accessed February 27, 2024)
Created January 31, 2017, Updated October 12, 2021