Lattice thermal conductivity of TixZryHf1-x-yNiSn half-Heusler alloys calculated from first principles: Key role of nature of phonon modes
Lattice thermal conductivity of TixZryHf1-x-yNiSn half-Heusler alloys calculated from first principles: Key role of nature of phonon modes
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DOI：
10.1103/physrevb.95.045202
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发表时间：
2017-01-11
影响因子：
3.7
通讯作者：
Berland, Kristian
中科院分区：
文献类型：
--
作者：
Eliassen, Simen N. H.;Katre, Ankita;Berland, Kristian
尽管XNiSn（X = Ti、Zr或Hf）半赫斯勒化合物具有相对高的晶格热导率kappa（1），但它们是良好的热电材料。先前的研究表明，kappa（l）可以通过X位点上的亚晶格合金化来降低。为了阐明合金成分如何影响kappa（l），我们使用弛豫时间近似下的声子玻尔兹曼输运方程并结合密度泛函理论来研究该系统。通过质量无序散射合金化的效果进行了探索，使用虚晶近似筛选整个三元TixHf 1-x-yNiSn相图。对于TixHf 1-x-yNiSn组合物发现最低的晶格热导率;特别地，当Ti含量在20%和80%之间变化时，存在以Ti 0.5Hf0.5NiSn为中心的浅最小值，其中kappa（l）取3.2和4.1W/mK之间的值。有趣的是，在这个系统中的质量无序散射的整体行为只能从声子模式的性质和质量方差的大小的组合来理解。质量无序散射在散射低能量的声学声子时是无效的。通过使用一个简单的模型的晶界散射，我们发现，纳米结构这些化合物可以有效地散射这样的声子，从而进一步降低晶格热导率，例如，Ti0.5Hf0.5NiSn与晶粒尺寸L = 100 nm的经验相比，单晶的kappa（1）的42%的减少。
In spite of their relatively high lattice thermal conductivity kappa(l), the XNiSn (X = Ti, Zr, or Hf) half-Heusler compounds are good thermoelectric materials. Previous studies have shown that kappa(l) can be reduced by sublattice alloying on the X site. To cast light on how the alloy composition affects kappa(l), we study this system using the phonon Boltzmann-transport equation within the relaxation time approximation in conjunction with density functional theory. The effect of alloying through mass-disorder scattering is explored using the virtual crystal approximation to screen the entire ternary TixHf1-x-yNiSn phase diagram. The lowest lattice thermal conductivity is found for the TixHf1-x-yNiSn compositions; in particular, there is a shallow minimum centered at Ti0.5Hf0.5NiSn with kappa(l) taking values between 3.2 and 4.1 W/mK when the Ti content varies between 20% and 80%. Interestingly, the overall behavior of mass-disorder scattering in this system can only be understood from a combination of the nature of the phonon modes and the magnitude of the mass variance. Mass-disorder scattering is not effective at scattering acoustic phonons of low energy. By using a simple model of grain boundary scattering, we find that nanostructuring these compounds can scatter such phonons effectively and thus further reduce the lattice thermal conductivity; for instance, Ti0.5Hf0.5NiSn with a grain size of L = 100 nm experiences a 42% reduction of kappa(l) compared to that of the single crystal.