Off-center rattling and cage vibration of the carrier-tuned type-I clathrate Ba_8Ga_16Ge_30 studied by Raman scattering
Off-center rattling and cage vibration of the carrier-tuned type-I clathrate Ba_8Ga_16Ge_30 studied by Raman scattering
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DOI：
10.1103/physrevb.82.134302
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发表时间：
2010-10
影响因子：
3.7
通讯作者：
Y. Takasu;T. Hasegawa;N. Ogita;M. Udagawa;M. Avila;K. Suekuni;T. Takabatake
中科院分区：
文献类型：
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作者：
Y. Takasu;T. Hasegawa;N. Ogita;M. Udagawa;M. Avila;K. Suekuni;T. Takabatake
为了揭示I型笼形化合物中客体离子的动力学性质，用拉曼散射研究了n型和p型笼形化合物Ba_8Ga_（16）Ge_（30）.据发现，客体离子在6d-位笼6d-笼旋转移动的n-和p-型，因为额外的客人模式EgA已被观察到，无论其载体。6d笼中100和110方向之间的势能差与客体离子位置离笼中心的偏心距离成比例，并且p型的偏心距离远大于n型Ba8Ga16Ge30的偏心距离。另外，在6c位置的笼振动的拉曼强度，p型比n型弱。因此，对于p型，6c位置处的振动的振幅变小，并且该小振幅引起用于客体离子的大的可移动空间，即，6C位原子的这种振动幅度用作偏离中心位置的势垒。对于这两个系统，在6d笼中的客体离子显示出非谐振动，从客体离子的异常能量随温度降低而降低判断。T2g和T1u的能量差为T. Mori等人，物理评论B 79，212301 2009年的客人模式清楚地支持了理论预测的相互作用的偶极子图片，解释了玻璃状的性能的偏心包合物。结果表明，偏心振动对晶格热导率的抑制起着重要的作用。
To reveal dynamical property of a guest ion in type-I clathrate compound, n- and p-type clathrates Ba8Ga16Ge30 have been investigated by Raman scattering. It is found that the guest ion in a 6d-site cage 6d-cage rotationally moves for both n- and p-type since the additional guest mode EgA has been observed regardless of its carrier. The potential-energy difference between 100 and 110 directions in the 6d-cage is proportional to the off-center distance of the guest-ion position from the cage center and this off-center distance for p-type is much larger than that for n-type Ba8Ga16Ge30. In addition, the Raman intensity of the cage vibration at a 6c site for p-type is weaker than that for n-type. Thus, the amplitude of the vibration at the 6c site becomes small for p-type, and this small amplitude induces a large movable space for the guest ion, i.e., this vibrational amplitude of the 6c-site atom works as the barrier for the off-center position. For both systems, the guest ion in the 6d-cage shows an anharmonic vibration, judging from the anomalous energy decrease in the guest ion with decreasing temperature. The energy difference between T2g and T1u T. Mori et al., Phys. Rev. B 79, 212301 2009 of the guest mode clearly supports the theoretical prediction of an interacting dipoles picture that explains the glasslike properties of the off-centered clathrate. It is concluded that the off-center rattling plays an important role to suppress a lattice thermal conductivity.