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Journal Articles Physical Review Materials Year : 2022

Site independent strong phonon-vacancy scattering in high temperature ceramics ZrB and HfB

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Abstract

Similar effects of metal and boron vacancies on phonon scattering and lattice thermal conductivity (κl) of ZrB2 and HfB2 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 boron vacancy that substantially changes the interatomic force constants. In contrast, a long ranged but weaker perturbation is seen in the case of metal vacancy. We show that these behaviors originate from a mixed metallic and covalent bonding nature in the metal diborides. The thermal transport calculations are performed in a complete ab initio framework based on Boltzmann transport equation and density functional theory. Phonon-vacancy scattering is calculated using ab initio Green█s function approach. Effects of natural isotopes and grain boundaries on κl 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 purecrystal limits. Our results outline significant material design aspects for these multifunctional high-temperature ceramics.
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cea-03891396 , version 1 (09-12-2022)

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Vrishali Sonar, Rohan Dehankar, K. P. Vijayalakshmi, Natalio Mingo, Ankita Katre. Site independent strong phonon-vacancy scattering in high temperature ceramics ZrB and HfB. Physical Review Materials, 2022, 6, pp.065403. ⟨10.1103/PhysRevMaterials.6.065403⟩. ⟨cea-03891396⟩
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