Journal Article

PreJuSER-10938

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png A study of low-energy guest phonon modes in clathrate-II NaxSi136 (x = 3, 23, and 24)

Beekman, M. ; Hermann, R.FZJ* ; Möchel, A.FZJ* ; Juranyi, F. ; Nolas, G. S.

2010
IOP Publ. Bristol

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Please use a persistent id in citations: doi:10.1088/0953-8984/22/35/35401

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.

Keyword(s): J

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].

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Contributing Institute(s):

1. Streumethoden (IFF-4)
2. Neutronenstreuung (IFF-5)
3. Jülich-Aachen Research Alliance - Fundamentals of Future Information Technology (JARA-FIT)
4. JCNS (Jülich Centre for Neutron Science JCNS (JCNS) ; JCNS)

Research Program(s):

1. BioSoft: Makromolekulare Systeme und biologische Informationsverarbeitung (P45)
2. Großgeräte für die Forschung mit Photonen, Neutronen und Ionen (PNI) (P55)

Appears in the scientific report 2010

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