NMR relaxation and rattling phonons in the type-I Ba8 Ga16 Sn30 clathrate

Xiang Zheng, Sergio Y. Rodriguez, and Joseph H. Ross, Jr.

Phys. Rev. B 84, 024303 (2011).

Atomic motion of guest atoms inside semiconducting clathrate cages is considered an important source for glasslike thermal behavior. 69Ga and 71Ga nuclear magnetic resonance studies on type I Ba8Ga16Sn30 show a clear low-temperature relaxation peak attributed to the influence of Ba rattling dynamics on the framework-atom resonance, with a quadrupolar relaxation mechanism as the leading contribution. Data are analyzed using a two-phonon Raman process, according to a recent theory involving localized anharmonic oscillators. Excellent agreement is obtained using this model, with the parameters corresponding to a uniform array of localized oscillators with very large anharmonicity.

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