热电笼状物声子作用对其反常比热容的影响

Impact of the phonon interactions on the anomalous specific heat of thermoelectric clathrates

摘要:

笼状物材料具有极低的晶格热导率，表现出非常优秀的热电性能. 但是，笼状物中束缚在笼子中的原子与笼子的相互作用形式尚不明确，这种相互作用与其反常热力学性质的关系仍有很多争议. 使用从头算晶格动力学计算方法计算笼状物Ba8Ga16Ge30 (BGG)的声子以及比热容，利用同位素Ge-76替换的方法研究束缚原子与笼子的相互作用. 结果表明，束缚原子与笼子之间存在着明显的耦合作用，这种耦合作用对笼状物反常热力学行为的产生具有重要意义.

Abstract:

Clathrates are extraordinary thermoelectric materials due to their low thermal conductivity. However, it is generally assumed that the atoms captured in the cages, so-called the guests, act as “rattlers” inducing disordered lattice dynamics and unusual thermal properties. Here, the isotope Ge-76 has an evident influence on the phonons and the heat capacity of Ba8Ga16Ge30 (BGG) by using ab initio lattice dynamics calculations. The results verify the intense coupling between the guest and host lattice which contributesto the anomalous specific heat. This finding paves the way for understanding the microscopic mechanism of clathrates and designing the thermoelectric materials with high performance.