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arXiv 2003.05506cond-mat.mtrl-sci
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多口袋型Full-Heusler化合物的高热电性能和缺陷能学

High Thermoelectric Performance and Defect Energetics of Multi-pocketed Full-Heusler Compounds

Junsoo Park, Yi Xia, Alex Ganose, Anubhav Jain, Vidvuds Ozolins

摘要:

采用第一性原理密度泛函方法研究了全Heusler化合物Sr $_{2}$ BiAu和Sr $_{2}$ SbAu的电子-声子相互作用和热电输运性质.我们的研究结果表明,在很宽的温度范围内的非本征体热电性能是物理上可能的,并指出存在的多重简并和高度分散的载流子口袋作为实现它的关键因素。Sr $_{2}$ BiAu,它具有10个能量对准的低有效质量口袋(6个沿$Γ-X$和4个在$L$),预计提供$n$型$zT=0.4-4.9$在$T=100-700$ ~K。与先前研究的Ba $_{2}$ BiAu化合物的比较表明,在Sr $_{2}$ BiAu中的额外的$L$ -口袋显著地增加了其低温功率因数,在$T=300$ ~K附近达到最大值$12$ ~mW~m $^{-1}$ ~K $^{-2}$。然而,在高温下,Sr $_{2}$ BiAu的功率因数下降到Ba $_{2}$ BiAu的功率因数以下,因为$L$态较重并且受到声子变形的强散射,而不是受偏振光散射限制的较轻的$Γ-X$态。预测Sr $_{2}$ SbAu在$T=750$ ~K下递送较低的$n$型$zT=3.4$,这是由于$L$和$Γ-X$载体袋之间的明显未对准、通常较重的散射和略高的晶格热导率。负责低晶格热导率的软声模式也增加了Heusler化合物的振动熵和高温稳定性,这表明它们的实验合成可能是可行的。占主导地位的本征缺陷被发现是Au空位,其驱动费米能级朝向导带并且有利于$n$掺杂。

英文摘要:

We report first-principles density-functional study of electron-phonon interactions and thermoelectric transport properties of full-Heusler compounds Sr$_{2}$BiAu and Sr$_{2}$SbAu. Our results show that ultrahigh intrinsic bulk thermoelectric performance across a wide range of temperatures is physically possible and point to the presence of multiply degenerate and highly dispersive carrier pockets as the key factor for achieving it. Sr$_{2}$BiAu, which features ten energy-aligned low effective mass pockets (six along $Γ-X$ and four at $L$), is predicted to deliver $n$-type $zT=0.4-4.9$ at $T=100-700$~K. Comparison with the previously investigated Ba$_{2}$BiAu compound shows that the additional $L$-pockets in Sr$_{2}$BiAu significantly increase its low-temperature power factor to a maximum value of $12$~mW~m$^{-1}$~K$^{-2}$ near $T=300$~K. However, at high temperatures the power factor of Sr$_{2}$BiAu drops below that of Ba$_{2}$BiAu because the $L$ states are heavier and subject to strong scattering by phonon deformation as opposed to the lighter $Γ-X$ states that are limited by polar-optical scattering. Sr$_{2}$SbAu is predicted to deliver lower $n$-type of $zT=3.4$ at $T=750$~K due to appreciable misalignment between the $L$ and $Γ-X$ carrier pockets, generally heavier scattering, and slightly higher lattice thermal conductivity. Soft acoustic modes, responsible for low lattice thermal conductivity, also increase vibrational entropies and high-temperature stability of the Heusler compounds, suggesting that their experimental synthesis may be feasible. The dominant intrinsic defects are found to be Au vacancies, which drive the Fermi level towards the conduction band and work in favor of $n$-doping.

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