高温陶瓷ZrB $_2$和HfB $_2$中与格位无关的强声子-空位散射
Site independent strong phonon-vacancy scattering in high temperature ceramics ZrB$_2$ and HfB$_2$
摘要：
金属和硼空位对ZrB $_2$和HfB $_2$的声子散射和晶格热导率（$κ_l$）的影响相似。这些缺陷挑战了将较大影响与较大缺陷相关联的传统理解。我们发现其根本原因是由硼空位引起的强烈的局域扰动，它大大改变了原子间的力常数。与此相反，在金属空位的情况下，一个长期的，但较弱的扰动。我们表明，这些行为起源于混合金属和共价键的金属二硼化物的性质。在基于Boltzmann输运方程和密度泛函理论的完整的\textit{ab initio}框架下进行了热输运计算。用\textit{ab initio}格林函数方法计算了声子-空位散射。天然同位素和晶界对$κ_l$的影响也进行了系统的研究，但我们发现一个有影响力的作用，空位解释实验中看到的大的变化。我们进一步报告了两个数量级的差异之间的非晶和纯晶体的限制。我们的研究结果概述了这些多功能高温陶瓷的重要材料设计方面。
英文摘要：
Similar effects of metal and boron vacancies on phonon scattering and lattice thermal conductivity ($κ_l$) of ZrB$_2$ and HfB$_2$ are reported. These defects challenge the conventional understanding that associates larger impacts to bigger defects. We find the underlying reason to be a strong local perturbation caused by the boron vacancy that substantially changes the interatomic force constants. In contrast, a long ranged but weaker perturbation is seen in the case metal vacancies. We show that these behaviours originate from a mixed metallic and covalent bonding nature in the metal diborides. The thermal transport calculations are performed in a complete \textit{ab initio} framework based on Boltzmann transport equation and density functional theory. Phonon-vacancy scattering is calculated using \textit{ab initio} Green's function approach. Effects of natural isotopes and grain boundaries on $κ_l$ are also systematically investigated, however we find an influential role of vacancies to explain large variations seen in the experiments. We further report a two-order of magnitude difference between the amorphous and pure-crystal limits. Our results outline significant material design aspects for these multi-functional high temperature ceramics.
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