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Dynamics of Pyramidal SiH3- Ions in ASiH(3) (A = K and Rb) Investigated with Quasielastic Neutron Scattering

Carin Österberg (Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; H. Fahlquist ; U. Haussermann ; C. M. Brown ; T. J. Udovic ; Maths Karlsson (Institutionen för fysik, Kondenserade materiens fysik (Chalmers))
Journal of Physical Chemistry C (1932-7447). Vol. 120 (2016), 12, p. 6369-6376.
[Artikel, refereegranskad vetenskaplig]

The two alkali silanides ASiH(3) (A = K and Rb) were investigated by means of quasielastic neutron scattering, both below and above the order-disorder phase transition occurring at around 275-300 K. Measurements upon heating show that there is a large change in the dynamics on going through the phase transition, whereas measurements upon cooling reveal a strong hysteresis due to undercooling of the disordered phase. The results show that the dynamics is associated with rotational diffusion of SiH3- anions, adequately modeled by H-jumps among 24 different jump locations radially distributed around the Si atom. The average relaxation time between successive jumps is of the order of subpicoseconds and exhibits a weak temperature dependence with a small difference in activation energy between the two materials, 39(1) meV for KSiH3 and 33(1) meV for RbSiH3. The pronounced SiH3- dynamics explains the high entropy observed in the disordered phase resulting in the low entropy variation for hydrogen absorption/desorption and hence the origin of these materials' favorable hydrogen storage properties.

Nyckelord: hydrogen-storage materials; borohydrides mbh4 m; tetrahydroborate; anions; potassium silanide; crystal-structures; aluminum hydrides; libh4; silyl; lithium; ksih3; Chemistry; Science & Technology – Other Topics; Materials Science

Denna post skapades 2016-05-04. Senast ändrad 2016-06-02.
CPL Pubid: 235962


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Denna publikation är ett resultat av följande projekt:

New insights in hydrogenous materials for energy (VR//2010-3519)