Off-center rattling modes and glasslike thermal conductivity in the type-I clathrate Ba 8 Ga 16 Sn 30
Off-center rattling modes and glasslike thermal conductivity in the type-I clathrate Ba 8 Ga 16 Sn 30
复制标题
DOI：
10.1103/physrevb.81.205207
复制
发表时间：
2010-05
影响因子：
3.7
通讯作者：
K. Suekuni;Y. Takasu;T. Hasegawa;N. Ogita;M. Udagawa;M. Avila;T. Takabatake
中科院分区：
文献类型：
--
作者：
K. Suekuni;Y. Takasu;T. Hasegawa;N. Ogita;M. Udagawa;M. Avila;T. Takabatake
I 型包合物 ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ 在晶格导热系数 ${\ensuremath{\kappa}}_{\text{L}}$ 中表现出玻璃般的行为，无论载流子类型如何。为了更好地理解这种行为与客体振动之间的关系，对载流子调谐单晶进行了偏振拉曼散射测量。 ${E}_{g}$ 对称谱中对称禁止模式的出现表明 Ba 原子在十四面体的偏离中心位置之间旋转。从 300 冷却到 4 K 时，${E}_{g}$ 和 ${T}_{2g}$ 客体模式的能量分别降低 15% 和 25%。这种急剧的下降源于原子位移四次项的强非谐势。 4 K 时 ${T}_{2g}$ 模式的 $14\text{ }{\text{cm}}^{\ensuremath{-}1}$ 的能量是金属间包合物中最低的。 ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ 的结果与 I 型 ${\text{Eu}}_{8}{\text{Ga}}_{16}{\text{Ge}}_{30}$ 的结果进行比较， ${\text{Sr}}_{8}{\text{Ga}}_{16}{\text{Ge}}_{30}$ 的 ${\ensuremath{\kappa}}_{\text{L}}(T)$ 表现出类似的玻璃状行为，并具有稳定状态。三个系统之间的比较表明，客体振动能量与 ${\ensuremath{\kappa}}_{\text{L}}(T)$ 中高原的温度范围成正比。
Type-I clathrate ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ is unique for showing glasslike behavior in the lattice thermal conductivity ${\ensuremath{\kappa}}_{\text{L}}$ 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 ${E}_{g}$ 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 ${E}_{g}$ and ${T}_{2g}$ 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 $14\text{ }{\text{cm}}^{\ensuremath{-}1}$ for the ${T}_{2g}$ mode at 4 K is the lowest among intermetallic clathrates. These results for ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ are compared with those for type-I ${\text{Eu}}_{8}{\text{Ga}}_{16}{\text{Ge}}_{30}$ and ${\text{Sr}}_{8}{\text{Ga}}_{16}{\text{Ge}}_{30}$ whose ${\ensuremath{\kappa}}_{\text{L}}(T)$ 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 ${\ensuremath{\kappa}}_{\text{L}}(T)$.