Ultralow lattice thermal conductivity of the fully filled skutterudite YbFe4Sb12 due to the flat avoided-crossing filler modes
Ultralow lattice thermal conductivity of the fully filled skutterudite YbFe4Sb12 due to the flat avoided-crossing filler modes
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DOI：
10.1103/physrevb.91.144304
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发表时间：
2015-04-15
影响因子：
3.7
通讯作者：
Mingo, Natalio
中科院分区：
文献类型：
--
作者：
Li, Wu;Mingo, Natalio
从第一性原理出发，研究了YbFe 4Sb 12和BaFe 4Sb 12的晶格热导率（kappa）。计算的YbFe 4Sb 12的kappa值比BaFe 4Sb 12的kappa值低10倍，远低于其他方钴矿的kappa值。YbFe_4Sb_（12）的超低卡伯值与Yb主导的平坦模密切相关，这些模出现在5 ~ 7.2rad/ps的频率范围内。平坦模显著增加了三声子散射通道，这反映在加权相空间的独特特性上，导致了更强的中频光学声子非谐散射。虽然这些平坦模式占主导地位的Yb原子，填料相关的非谐相互作用不发挥作用，在增加的声子散射。这强调了在那些平坦模式中填料和主体基质的杂化的重要性，这可以通过避免与声学声子的交叉来保证。与其他方钴矿相同的被压抑的声子谱机制也在超低kappa中起作用。我们的工作提出了一个减少机制的kappa的笼状结构，如方钴矿和笼形物中的填料，并证明了这些材料中的还原机制的非唯一性。
We study the lattice thermal conductivity (kappa) of fully filled skutterudites YbFe4Sb12 and BaFe4Sb12 from first principles. The calculated kappa of YbFe4Sb12 is ten times lower than that calculated for BaFe4Sb12, and much lower than any values ever reported for other skutterudites. The ultralow kappa of YbFe4Sb12 is closely related to the flat Yb-dominated modes appearing in the frequency range from 5 to 7.2 rad/ps. The flat modes significantly increase the three-phonon scattering channels, which is reflected by the unique characteristics of weighted phase space and leads to much stronger anharmonic scattering of intermediate-frequency optical phonons. Although those flat modes are dominated by the Yb atoms, the filler-related anharmonic interaction does not play a role in the increased phonon scattering. This underlines the importance of the hybridization of the filler and the host matrix in those flat modes, which can be guaranteed by the avoided crossing with acoustic phonons. The depressed phonon spectrum mechanism, common to other skutterudites, also plays a role in the ultralow kappa. Our work presents a reduction mechanism of kappa by the filler in cage-like structures such as skutterudites and clathrates, and demonstrates the nonuniqueness of the reduction mechanism in these materials.