Mukhopadhyay Saikat, Lindsay Lucas, Singh David J
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA.
Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211-7010 USA.
Sci Rep. 2016 Nov 16;6:37076. doi: 10.1038/srep37076.
The lattice thermal conductivity (κ) of hexagonal GeSbTe (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy (κ/κ~2) of κ in bulk h-GST, with the dominant contribution to κ from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes are the majority heat carriers in typical semiconductors and insulators. The anisotropy derives from varying bonding along different crystal directions, specifically from weak interlayer bonding along the c-axis, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The large optic mode contributions to the thermal conductivity in low-κ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials.
通过直接第一性原理计算研究了六方晶系GeSbTe（h-GST）的晶格热导率（κ）。我们发现块状h-GST中κ存在显著的本征各向异性（κ/κ~2），其中光学声子对κ的贡献占主导，约为75%。这极为不寻常，因为在典型半导体和绝缘体中，声学声子模式是主要的热载流子。这种各向异性源于沿不同晶体方向键合的变化，具体而言是沿c轴的层间弱键合，这导致了各向异性的声子色散。h-GST的声子谱具有非常色散的光学分支，与沿c轴的平坦光学带相比，沿a轴具有更高的群速度。在低κ的h-GST中，光学模式对热导率的大贡献是不寻常的，对这些贡献的基本物理理解的发展可能对于更好地理解其他复杂层状材料中的热传导至关重要。
