Lattice Softening Significantly Reduces Thermal Conductivity and Leads to High Thermoelectric Efficiency
Lattice Softening Significantly Reduces Thermal Conductivity and Leads to High Thermoelectric Efficiency
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DOI：
10.1002/adma.201900108
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发表时间：
2019-05-01
影响因子：
29.4
通讯作者：
Snyder, G. Jeffrey
中科院分区：
文献类型：
--
作者：
Hanus, Riley;Agne, Matthias T.;Snyder, G. Jeffrey
微/纳米结构对热导率的影响是一个非常有科学意义的话题，特别是对于热电器件。目前的理解是，结构缺陷通过声子散射降低热导率，其中假设声子色散和声速保持恒定。实验工作的PbTe模型系统，这表明，声速线性降低增加内部应变。这种材料晶格的软化完全解释了晶格热导率的降低，而没有引入额外的声子散射机制。此外，它表明，一个主要的贡献，提高热电优值（zT > 2）的高效率Na掺杂的PbTe可以归因于晶格软化。虽然已知不均匀的内部应变场会引入声子散射中心，但本研究表明，内部应变也会改变声子的传播速度。这提出了新的途径来控制晶格热导率，超越声子散射。在实践中，许多工程材料将表现出软化和散射效应，如硅所示。这一工作为能源材料、微电子学和纳米尺度传热领域的热导率研究提供了新的思路。
The influence of micro/nanostructure on thermal conductivity is a topic of great scientific interest, particularly to thermoelectrics. The current understanding is that structural defects decrease thermal conductivity through phonon scattering where the phonon dispersion and speed of sound are assumed to remain constant. Experimental work on a PbTe model system is presented, which shows that the speed of sound linearly decreases with increased internal strain. This softening of the materials lattice completely accounts for the reduction in lattice thermal conductivity, without the introduction of additional phonon scattering mechanisms. Additionally, it is shown that a major contribution to the improvement in the thermoelectric figure of merit (zT > 2) of high-efficiency Na-doped PbTe can be attributed to lattice softening. While inhomogeneous internal strain fields are known to introduce phonon scattering centers, this study demonstrates that internal strain can modify phonon propagation speed as well. This presents new avenues to control lattice thermal conductivity, beyond phonon scattering. In practice, many engineering materials will exhibit both softening and scattering effects, as is shown in silicon. This work shines new light on studies of thermal conductivity in fields of energy materials, microelectronics, and nanoscale heat transfer.