Novel thermoelectrics emerging from multinary freedoms of clathrates encapsulating rare-earths and alkaline metals

金属间包合物虽然具有三维晶体结构，但具有玻璃样的导热性能，因此具有很高的热电转换器潜力。为了了解热导率降低的机理，我们通过结构精细化、热、超声、拉曼散射和光电发射测量等手段研究了包封碱土和稀土原子的i型包合物。结果表明，笼内放松空间中的客体可以在偏离中心的位置之间旋转，这种运动强烈地散射声子，从而降低了热导率。

Intermetallic clathrates have high potential as thermoelectric converters because of the glass-like thermal conductivity in spite of the three dimensional crystal structure. To understand the mechanism of the reduced thermal conductivity, we have studied type-I clathrates encapsulating alkaline-earth and rare-earth atoms by means of structural refinement, thermal, ultrasonic, Raman scattering and photoemission measurements. It is revealed that the guest in a relaxed space inside the cage can rotate among off-center sites and this motion strongly scatters acoustic phonons to reduce the thermal conductivity.