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See detailA study of low-energy guest phonon modes in clathrate-II NaxSi136 (x = 3, 23, and 24)
Beekman, M.; Hermann, Raphaël ULg; Möchel, Anne ULg et al

in Journal of Physics : Condensed Matter (2010)

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 ... [more ▼]

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. [less ▲]

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See detailMagnetic and electronic properties of Eu4Sr4Ga16Ge30
Woods, G. T.; Marti; Beekman, M. et al

in Physical Review b (2006), 73(17),

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu4Sr4Ga16Ge30, a type I clathrate that has ... [more ▼]

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu4Sr4Ga16Ge30, a type I clathrate that has divalent strontium and europium ions encapsulated within a Ga-Ge framework. These data are compared with those of type I clathrates Eu8Ga16Ge30 and Eu6Sr2Ga16Ge30. The ferromagnetic ordering of these Eu-containing clathrates is substantially altered by the incorporation of strontium, as compared to Eu8Ga16Ge30. Ferromagnetism, accompanied by a relatively large negative magnetoresistance, is observed below 15 and 20 K in Eu4Sr4Ga16Ge30 and Eu6Sr2Ga16Ge30, respectively. An effective magnetic moment of 7.83 mu(B) per Eu ion is observed above 30 K for Eu4Sr4Ga16Ge30, a moment which is close to the free-ion moment of 7.94 mu(B) per europium(II) ion. [less ▲]

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