发表机构
University of Science and Technology Beijing（北京科技大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过第一性原理计算发现，六方钙钛矿Cs$BX_3$的晶格热导率存在显著各向异性，源于中频光学声子的面外热输运通道，为非范德华晶体的热导率各向异性工程提供了新平台。
AI 中文摘要
具有强各向异性晶格热导率的材料是热管理应用的理想选择，但这类特性通常与层状或准一维范德华晶体以及高度各向异性的弹性质相关。本研究采用第一性原理计算，探究六方钙钛矿Cs$BX_3$（$B$=Mg、Cd；$X$=Cl、Br、I）的晶格热输运。在300K下，计算得到的面内与面外晶格热导率范围分别为0.13--0.83 Wm$^{-1}$K$^{-1}$和0.34--6.26 Wm$^{-1}$K$^{-1}$，对应各向异性比为2.6--7.5。考虑到弹性各向异性相对适中（$C_{33}/C_{11}$=0.994--1.842），这种显著的各向异性十分引人关注。分析表明，中频光学声子提供了高效的面外热输运通道，这与热输运由声学声子主导的传统图像相反。这些发现确定，共面八面体骨架是在力学近各向同性的非范德华晶体中设计强热导率各向异性的有潜力平台。
英文摘要
Materials exhibiting strongly anisotropic lattice thermal conductivity are desirable for thermal-management applications, yet such behavior is commonly associated with layered or quasi-one-dimensional van der Waals crystals and highly anisotropic elastic properties. Here, we investigate lattice thermal transport in the hexagonal perovskites Cs$BX_3$ ($B=$ Mg, Cd; $X=$ Cl, Br, I) using first-principles calculations. At 300~K, the calculated in-plane and out-of-plane lattice thermal conductivities range from 0.13--0.83 and 0.34--6.26~Wm$^{-1}$K$^{-1}$, respectively, corresponding to anisotropy ratios of 2.6--7.5. This pronounced anisotropy is remarkable given the relatively modest elastic anisotropy, characterized by $C_{33}/C_{11}$ = 0.994--1.842. Our analysis reveals that medium-frequency optical phonons provide an efficient out-of-plane heat-transport channel, contrary to the conventional picture in which heat transport is dominated by acoustic phonons. These findings identify face-sharing octahedral frameworks as a promising platform for engineering strong thermal-conductivity anisotropy in mechanically near-isotropic, non--van der Waals crystals.
Comments11 pages,6 figures
