Abstract The ability to relate the spatially-varying anisotropy of thermal conductivity to crystal structure would provide a foundational advance in our understanding of length-scale dependent heat flow. The challenge, however, is in determining the thermal conductivity tensor in polycrystalline systems with anisotropic crystal structures. Apparent isotropic thermal conductivity in randomly oriented polycrystals with anisotropic properties break down at length scales approaching the grain size. As a result, a measured isotropic thermal conductivity from the macroscale perspective may differ greatly from that measured at the nano or microscale, and thus microscale anisotropic heat flow could underlie a seemingly isotropic thermal conductivity. We experimentally investigate the anisotropic thermal conductivity in polycrystalline beta-phase yttrium disilicate (β-Y2Si2O7). This is achieved through micrometer-resolution thermal conductivity mapping correlated to the phase and orientation of individual grains, allowing for the determination of the thermal conductivity tensor of β-Y2Si2O7. Our results are the first to reproduce the thermal conductivity tensor of a polycrystalline system with anisotropic crystal structure based on the spatial distribution of thermal conductivity.

中文翻译：

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β-Y2Si2O7 的各向异性热导率张量，用于微米尺度热流的定向控制

摘要 将热导率的空间变化各向异性与晶体结构联系起来的能力将为我们理解与长度尺度相关的热流提供基础性的进步。然而，挑战在于确定具有各向异性晶体结构的多晶系统中的热导率张量。具有各向异性特性的随机取向多晶中的表观各向同性热导率在接近晶粒尺寸的长度尺度上分解。因此，从宏观角度测量的各向同性热导率可能与在纳米或​​微米尺度上测量的有很大不同，因此微米尺度各向异性热流可能是看似各向同性的热导率的基础。我们通过实验研究了多晶 β 相二硅酸钇 (β-Y2Si2O7) 的各向异性热导率。这是通过与单个晶粒的相和取向相关的微米分辨率热导率映射来实现的，从而可以确定 β-Y2Si2O7 的热导率张量。我们的结果是第一个基于热导率的空间分布再现具有各向异性晶体结构的多晶系统的热导率张量的结果。