二聚体振动模式在一种优良声导体中引起的低热导率
Dimer rattling mode induced low thermal conductivity in an excellent acoustic conductor
摘要：
具有较大声速的固体表现出较高的晶格热导率（k_{lat}）。钻石是一个突出的例子，它的平均声速是14400 m s-1和k_{lat}是2300 W m-1 K-1。在这里，我们报告一个极端的例外，CuP 2具有相当大的平均声速为4155 m s-1，相当于GaAs，但单晶显示出非常低的晶格热导率约为4 W m-1 K-1，在室温下，一个数量级小于GaAs。为了理解这样一个令人困惑的热输运行为，我们已经彻底研究了原子结构和晶格动力学相结合的中子散射技术与第一性原理模拟。铜原子形成夹在层状P原子网络之间的二聚体，并且二聚体以约11 meV的频率振动为振动模式。该模式表现为显著的非谐性并且强烈散射声学声子以实现低k_{lat}。这种层状结构中的二聚体晃动行为可能提供一种前所未有的抑制热传导的策略，而不涉及原子无序。
英文摘要：
A solid with larger sound speeds exhibits higher lattice thermal conductivity (k_{lat}). Diamond is a prominent instance where its mean sound speed is 14400 m s-1 and k_{lat} is 2300 W m-1 K-1. Here, we report an extreme exception that CuP2 has quite large mean sound speeds of 4155 m s-1, comparable to GaAs, but the single crystals show a very low lattice thermal conductivity of about 4 W m-1 K-1 at room temperature, one order of magnitude smaller than GaAs. To understand such a puzzling thermal transport behavior, we have thoroughly investigated the atomic structure and lattice dynamics by combining neutron scattering techniques with first-principles simulations. Cu atoms form dimers sandwiched in between the layered P atomic networks and the dimers vibrate as a rattling mode with frequency around 11 meV. This mode is manifested to be remarkably anharmonic and strongly scatters acoustic phonons to achieve the low k_{lat}. Such a dimer rattling behavior in layered structures might offer an unprecedented strategy for suppressing thermal conduction without involving atomic disorder.
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