Giant Anisotropic in-Plane Thermal Conduction Induced by Anomalous Phonons in Pentagonal PdSe2
Giant Anisotropic in-Plane Thermal Conduction Induced by Anomalous Phonons in Pentagonal PdSe2
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DOI：
10.1016/j.mtphys.2021.100599
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发表时间：
2021-07
影响因子：
11.5
通讯作者：
B. Wei;Junyan Liu;Q. Cai;A. Alatas;A. Said;Meihua Hu;Chen W. Li;Jia-wang Hong
中科院分区：
文献类型：
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作者：
B. Wei;Junyan Liu;Q. Cai;A. Alatas;A. Said;Meihua Hu;Chen W. Li;Jia-wang Hong
在二维材料中，不同的原子堆积方式会引起各向异性的原子相互作用和声子色散，从而导致面内热输运的各向异性。在这里，我们报告了一个例外的情况下，在层状五边形PdSe 2，其中的键，力常数和晶格常数是几乎相等的沿着面内晶轴方向，而热导率是令人惊讶的大得多沿b轴比沿a轴的比率高达1.8。如此强的各向异性不仅在面内均匀结构材料中是出乎意料的，而且与迄今报道的非均匀结构材料中的创纪录的高面内各向异性热导率（在TiS3中该比率为1.25）相当。通过结合非弹性X射线散射测量和第一性原理计算，我们将如此高的各向异性归因于沿轴的低能声子，特别是它们较低的群速度和“避免交叉”行为。PdSe 2的a轴（扁平型）和b轴（扁平型）的不同屈曲结构是其独特的声子动力学性质的主要原因。这一发现有助于发现均匀结构中具有高各向异性面内热导率的材料，并揭示了面内热导各向异性的新物理。由于PdSe2在结构和热传输性能方面的独特功能，PdSe2可以作为设计新型器件的新平台，以精确地在纳米尺度上路由热流。
In two-dimensional materials, different atomic stacking induces anisotropic atomic interactions and phonon dispersions, leading to the anisotropy of in-plane thermal transport. Here, we report an exceptional case in layered pentagonal PdSe2, where the bonds, force constants, and lattice constants are nearly-equal along the in-plane crystallographic axis directions, while the thermal conductivity is surprisingly much greater alongb-axis than alonga-axis with a ratio up to 1.8. Such strong anisotropy is not only unexpected in in-plane uniform structured materials, but also comparable to the record high in-plane anisotropic thermal conductivity in the nonuniform structured material reported to date (the ratio is ∼2.0 in TiS3). By combining the inelastic X-ray scattering measurement and the first-principles calculations, we attribute such high anisotropy to the low-energy phonons alonga-axis, particularly their lower group velocities and “avoided-crossing” behavior. The different buckling structures betweena- (zigzag-type) andb-axis (flat-type) are mainly responsible for such unique phonon dynamics properties of PdSe2. This finding helps to discover materials with high anisotropic in-plane thermal conductivity in uniform structures and reveals new physics of anisotropy of in-plane thermal conduction. Due to the unique features in structure and thermal transport properties, PdSe2 may serve as a new platform for designing novel devices to route heat flow precisely at the nanoscale.