FeVSb half-Heusler的第一性原理电子结构、声子性质、晶格热导率和优值预测
First-principles electronic structure, phonon properties, lattice thermal conductivity and prediction of figure of merit of FeVSb half-Heusler
摘要：
本文采用FP-LAPW方法和SCAN meta-GGA方法研究了一种有前途的热电半Heusler FeVSb的电子结构。使用所获得的电子结构和输运计算，我们试图解决实验Seebeck系数$S$的FeVSb样品。实验和计算的$S$之间的良好一致性表明，带隙可以是$\sim$ 0.7 eV。这得到了所获得的$\sim$ 0.7 eV的mBJ带隙的支持。在此基础上，我们研究并报道了声子色散、态密度和热力学性质。通过非解析项修正，还考虑了长程库仑相互作用对声子频率的影响。在准谐波近似下，计算了1200 K以下的热膨胀行为。在考虑声子-声子相互作用的单模弛豫时间近似下，采用第一性原理非简谐声子计算方法，得到了FeVSb的晶格热导率$κ_{ph}$.在300 K时，计算的$κ_{ph}$为$\sim$ 18.6 W $m^{-1}K^{-1}$，比实验值高。但在500 K以上，计算的$κ_{ph}$与实验符合较好.通过寻找最佳载流子浓度，对p型和n型FeVSb的优值$ZT$和效率进行了预测。在1200 K时，p型和n型FeVSb的最大$ZT$分别为$\sim$ 0.66和$\sim$ 0.44。对于p型和n型材料，在1200 K和300 K的高温和低温下，最大效率分别为$\sim$ 12.2%和$\sim$ 6.0%.还讨论了通过各种元素掺杂/空位实现n型和p型FeVSb的可能性。本文的研究为进一步开发FeVSb热电材料提供了理论依据。
英文摘要：
In this work, we have studied the electronic structure of a promising thermoelectric half-Heusler FeVSb using FP-LAPW method and SCAN meta-GGA including spin-orbit coupling. Using the obtained electronic structure and transport calculations we try to address the experimental Seebeck coefficient $S$ of FeVSb samples. The good agreement between the experimental and calculated $S$ suggests the band gap could be $\sim$0.7 eV. This is supported by the obtained mBJ band gap of $\sim$0.7 eV. Further, we study and report the phonon dispersion, density of states and thermodynamic properties. The effect of long range Coulomb interactions on phonon frequencies are also included by non-analytical term correction. Under quasi-harmonic approximation, the thermal expansion behaviour upto 1200 K is calculated. Using the first-principles anharmonic phonon calculations, the lattice thermal conductivity $κ_{ph}$ of FeVSb is obtained under single-mode relaxation time approximation considering the phonon-phonon interaction. At 300 K, the calculated $κ_{ph}$ is $\sim$18.6 W$m^{-1}K^{-1}$ which is higher compared to experimental value. But, above 500 K the calculated $κ_{ph}$ is in good agreement with experiment. A prediction of figure of merit $ZT$ and efficiency for p-type and n-type FeVSb is made by finding out optimal carrier concentration. At 1200 K, a maximum $ZT$ of $\sim$0.66 and $\sim$0.44 is expected for p-type and n-type FeVSb, respectively. For p-type and n-type materials, maximum efficiency of $\sim$12.2 \% and $\sim$6.0 \% are estimated for hot and cold temperature of 1200 K and 300 K, respectively. A possibility of achieving n-type and p-type FeVSb by various elemental doping/vacancy is also discussed. Our study is expected to help in further exploring the thermoelectric material FeVSb.
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