Type-I clathrate Ba8Ga16Sn30 is unique for showing glasslike behavior in the lattice thermal conductivity κL irrespective of the charge carrier type. For better understanding the relation between this behavior and guest rattling, polarized Raman-scattering measurements have been performed on carrier-tuned single crystals. The appearance of a symmetry-forbidden mode in the Eg symmetry spectrum indicates that the Ba atoms are rotating among the off-center positions in the tetrakaidecahedron. On cooling from 300 to 4 K, the energies of Eg and T2g guest modes decrease by 15% and 25%, respectively. This drastic decrease originates from the strongly anharmonic potential with a quartic term of the atomic displacement. The energy of 14 cm-1 for the T2g mode at 4 K is the lowest among intermetallic clathrates. These results for Ba8Ga 16Sn30 are compared with those for type-I Eu 8Ga16Ge30 and Sr8Ga 16Ge30 whose κL (T) show similar glasslike behavior with a plateau. The comparison between three systems indicates that the guest rattling energy is proportional to the temperature range of the plateau in κL (T).
|ジャーナル||Physical Review B - Condensed Matter and Materials Physics|
|出版ステータス||出版済み - 5月 19 2010|
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