Dynamics of Pyramidal SiH3‿/sup> Ions in ASiH3 (A = K and Rb) Investigated with Quasielastic Neutron Scattering

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• 作者：Carin Österberg ; Henrik Fahlquist ; Ulrich Häussermann ; Craig M. Brown ; Terrence J. Udovic ; Maths Karlsson
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：March 31, 2016
• 年：2016
• 卷：120
• 期：12
• 页码：6369-6376
• 全文大小：529K
• ISSN：1932-7455

文摘

The two alkali silanides ASiH₃ (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.