海归学者发起的公益学术平台
分享信息，整合资源
交流学术，偶尔风月
人们通常认为金属中声子贡献的热导率可以忽略，而热导率只由电子贡献。近来通过对电子和声子输运的第一性原理计算，发现在金属钨中声子贡献的热导率高达46 W/m-K，相当于其电子热导率的30%。高声子热导率是由于原子间非简谐相互作用引起的声子-声子散射很弱，尤其对高频声子。这也导致了电子-声子散射也对输运起到了重要的影响，造成了声子热导率具有反常的弱的温度依赖性。
来自深圳大学高等研究院的李武研究员课题组，在前期工作基础上，通过对高对称方向上的声子散射分析，发现金属钨的声子反常输运行为跟自身的单质体心立方结构紧密相关。在单质体心立方结构中，声子振动频率在高对称点P和H三重简并，在这些点散射通道被完全抑制，故声子-声子散射率在这些点严格为零。这造成了大的声子热导率并使得电子-声子散射占主导地位，进一步导致声子热导率的反常温度依赖性。而对于包含碱金属在内的其他多数bcc金属，又由于在某些方向的声子频率会远远小于其他方向，在这些高对称点声子散射将不再为零。该工作解释了在单质金属中为什么只有钨等少数几种材料的Lorenz数比理论值有显著差异。
该文近期发表于npj Computational Materials 5: 98 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。
Body-centered-cubic structure and weak anharmonic phonon scattering in tungsten
Yani Chen, Jinlong Ma, Shihao Wen & Wu Li
It was recently found that the anharmonic phonon–phonon scattering in tungsten is extremely weak at high frequencies, leading to a predominance of electron–phonon scattering and consequently anomalous phonon transport behaviors. In this work, we calculate the phonon linewidths of W along high-symmetry directions from first principles. We find that the weak phonon–phonon scattering can be traced back to two factors. The first is the triple degeneracy of the phonon branches at the P and H points, a universal property of elemental body-centered-cubic (bcc) structures. The second is a relatively isotropic character of the phonon dispersions. When both are met, phonon–phonon scattering rates must vanish at the P and H points. The weak phonon–phonon scattering feature is also applicable to Mo and Cr. However, in other elemental bcc substances like Na, the isotropy condition is violated due to the unusually soft character of the lower transverse acoustic phonon branch along the Γ-N direction, opening emission channels and leading to much stronger phonon–phonon scattering. We also look into the distributions of electron mean-free paths (MFPs) at room temperature in tungsten, which can help engineer the resistivity of nanostructured W for applications such as interconnects.
本文系网易新闻·网易号“各有态度”特色内容
媒体转载联系授权请看下方