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

Janos Mink ; Yuan-Chih Lin (Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; Maths Karlsson (Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; Carin Österberg (Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; Terrence J. Udovic ; Henrik Fahlquist ; Ulrich Häussermann
Journal of Raman Spectroscopy (0377-0486). Vol. 48 (2017), 2, p. 284-291.
[Artikel, refereegranskad vetenskaplig]

The hydrogen storage materials ASiH(3) (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 (-modifications). At temperatures below 200K, ASiH(3) exist as ordered low-temperature () modifications. The vibrational properties of -ASiH(3) 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 -RbSiH3. This correlates with a lower temperature for the - 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 ASiH(3) compare well to those of alkali metal borohydrides ABH(4) (A=Na-Cs).

Nyckelord: alkali metal silanides; complex metal hydrides; inelastic neutron scattering; libration modes; order–disorder phase transition

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Denna post skapades 2017-03-08. Senast ändrad 2017-09-20.
CPL Pubid: 248482


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