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@ARTICLE{Beekman:10938,
      author       = {Beekman, M. and Hermann, R. and Möchel, A. and Juranyi, F.
                      and Nolas, G. S.},
      title        = {{A} study of low-energy guest phonon modes in
                      clathrate-{II} {N}ax{S}i136 (x = 3, 23, and 24)},
      journal      = {Journal of physics / Condensed matter},
      volume       = {22},
      issn         = {0953-8984},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {PreJuSER-10938},
      pages        = {355401},
      year         = {2010},
      note         = {MB and GSN acknowledge support from US DOE Grant No.
                      DE-FG02-04ER46145 for crystal growth and specimen
                      preparation, as well as characterization and data analysis.
                      MB acknowledges support from the University of South Florida
                      Presidential Doctoral Fellowship. This work is based on
                      experiments performed at the Swiss spallation neutron source
                      SINQ, Paul Scherrer Institute, Villigen, Switzerland. The
                      FRM-2 is acknowledged for provision of the neutron beamtime
                      on PGAA, and Ms Lea Canella is acknowledged for assistance
                      during the data acquisition. The authors kindly thank
                      Kenneth I. Hardcastle of Emory University and Angus P
                      Wilkinson of Georgia Institute of Technology for
                      single-crystal x-ray diffraction data collection.
                      Single-crystal structure refinements were carried out with
                      the aid of the SHELX [30] and WinGX [31] software. Rietveld
                      refinements were carried out with the aid of the GSAS [32]
                      and EXPGUI software [33]. Figure 1 was drawn using the VESTA
                      software [34].},
      abstract     = {Single-crystal x-ray diffraction from clathrate-II NaxSi136
                      (x = 24) prepared by a new technique reveals the
                      exceptionally large Na@Si-28 atomic displacement parameter
                      (U-eq) is strongly temperature dependent, and can be
                      attributed to low-energy rattling modes associated with the
                      Na guest. Inelastic neutron scattering (INS) spectra
                      collected from NaxSi136 powder specimens (x = 3, 23) confirm
                      the presence of low-energy guest-derived phonon modes for
                      Na@Si-28 and Na@Si-20. The lower energy Na@Si-28 rattler
                      mode falls in the frequency range of the silicon host
                      acoustic phonons, indicating the possibility for interaction
                      with these phonons. The presence of these low-energy modes
                      combined with the ability to controllably vary the guest
                      content presents a unique opportunity for exploring the
                      influence of guest-framework interactions on the lattice
                      dynamics in intermetallic clathrates.},
      keywords     = {J (WoSType)},
      cin          = {IFF-4 / IFF-5 / JARA-FIT / Jülich Centre for Neutron
                      Science JCNS (JCNS) ; JCNS},
      ddc          = {530},
      cid          = {I:(DE-Juel1)VDB784 / I:(DE-Juel1)VDB785 /
                      $I:(DE-82)080009_20140620$ / I:(DE-Juel1)JCNS-20121112},
      pnm          = {BioSoft: Makromolekulare Systeme und biologische
                      Informationsverarbeitung / Großgeräte für die Forschung
                      mit Photonen, Neutronen und Ionen (PNI)},
      pid          = {G:(DE-Juel1)FUEK505 / G:(DE-Juel1)FUEK415},
      shelfmark    = {Physics, Condensed Matter},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000281422100014},
      doi          = {10.1088/0953-8984/22/35/35401},
      url          = {https://juser.fz-juelich.de/record/10938},
}