Mechanics of Materials Department, Sandia National Laboratories, Livermore, CA 94550, USA.
J Phys Condens Matter. 2012 Aug 15;24(32):325804, 1-15. doi: 10.1088/0953-8984/24/32/325804. Epub 2012 Jul 12.
The thermal conductivity of a crystal is sensitive to the presence of surfaces and nanoscale defects. While this opens tremendous opportunities to tailor thermal conductivity, true 'phonon engineering' of nanocrystals for a specific electronic or thermoelectric application can only be achieved when the dependence of thermal conductivity on the defect density, size and spatial population is understood and quantified. Unfortunately, experimental studies of the effects of nanoscale defects are quite challenging. While molecular dynamics simulations are effective in calculating thermal conductivity, the defect density range that can be explored with feasible computing resources is unrealistically high. As a result, previous work has not generated a fully detailed understanding of the dependence of thermal conductivity on nanoscale defects. Using GaN as an example, we have combined a physically motivated analytical model and highly converged large-scale molecular dynamics simulations to study the effects of defects on thermal conductivity. An analytical expression for thermal conductivity as a function of void density, size, and population has been derived and corroborated with the model, simulations, and experiments.
晶体的导热系数对表面和纳米级缺陷的存在很敏感。虽然这为调节导热系数提供了巨大的机会，但要对纳米晶体进行真正的“声子工程”以满足特定的电子或热电应用，就必须了解和量化导热系数对缺陷密度、尺寸和空间分布的依赖关系。不幸的是，纳米级缺陷的实验研究极具挑战性。虽然分子动力学模拟在计算导热系数方面非常有效，但在可行的计算资源范围内可探索的缺陷密度范围高得不切实际。因此，之前的工作并未完全深入了解导热系数对纳米级缺陷的依赖关系。我们以 GaN 为例，结合了物理启发的分析模型和高度收敛的大规模分子动力学模拟来研究缺陷对导热系数的影响。推导出了一个热导率作为空隙密度、尺寸和分布函数的解析表达式，并通过模型、模拟和实验进行了验证。
