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Title: Structural and dynamical trends in alkali-metal silanides characterized by neutron-scattering methods

Structural, vibrational, and dynamical properties of the mono- and mixed-alkali silanides (MSiH 3, where M = K, Rb, Cs, K 0.5Rb 0.5, K 0.5Cs 0.5, and Rb 0.5Cs 0.5) were investigated by various neutron experiments, including neutron powder diffraction (NPD), neutron vibrational spectroscopy (NVS), neutron-scattering fixed-window scans (FWSs), and quasielastic neutron scattering (QENS) measurements. Structural characterization showed that the mixed compounds exhibit disordered (α) and ordered (β) phases for temperatures above and below about 200–250 K, respectively, in agreement with their monoalkali correspondents. Vibrational and dynamical properties are strongly influenced by the cation environment; in particular, there is a red shift in the band energies of the librational and bending modes with increasing lattice size as a result of changes in the bond lengths and force constants. Additionally, slightly broader spectral features are observed in the case of the mixed compounds, indicating the presence of structural disorder caused by the random distribution of the alkali-metal cations within the lattice. FWS measurements upon heating showed that there is a large increase in reorientational mobility as the systems go through the order–disorder (β–α) phase transition, and measurements upon cooling of the α-phase revealed the known strong hysteresis for reversion back to themore » β-phase. Interestingly, at a given temperature, among the different alkali silanide compounds, the relative reorientational mobilities of the SiH 3 anions in the α- and β-phases tended to decrease and increase, respectively, with increasing alkali-metal mass. Lastly, this dynamical result might provide some insights concerning the enthalpy–entropy compensation effect previously observed for these potentially promising hydrogen storage materials.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [3] ;  [5] ;  [4]
  1. National Institute of Standards and Technology, Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
  2. National Institute of Standards and Technology, Gaithersburg, MD (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. Univ. de Picardie Jules Verne, Amiens Cedex (France)
  4. National Institute of Standards and Technology, Gaithersburg, MD (United States)
  5. Ural Branch of the Russian Academy of Sciences, Ekaterinburg (Russia)
Publication Date:
Report Number(s):
Journal ID: ISSN 1932-7447
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 120; Journal Issue: 38; Journal ID: ISSN 1932-7447
American Chemical Society
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; silanide properties; neutron experiments; characterization
OSTI Identifier: