Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai980-8579, Miyagi, Japan.
Nanochemistry Research Group, International Iberian Nanotechnology Laboratory (INL), Braga4715-330, Portugal.
ACS Appl Mater Interfaces. 2022 Dec 14;14(49):54736-54747. doi: 10.1021/acsami.2c16595. Epub 2022 Nov 30.
Intrinsically high lattice thermal conductivity has remained a major bottleneck for achieving a high thermoelectric figure of merit () in state-of-the-art ternary half-Heusler (HH) alloys. In this work, we report a stable n-type biphasic-quaternary (Ti,V)CoSb HH alloy with a low lattice thermal conductivity κ ≈ 2 W m K within a wide temperature range (300-873 K), which is comparable to the reported nanostructured HH alloys. A solid-state transformation driven by spinodal decomposition upon annealing is observed in TiVCoSb HH alloy, which remarkably enhances phonon scattering, while electrical properties correlate well with the altering electronic band structure and valence electron count (VEC). A maximum ≈ 0.4 (±0.05) at 873 K was attained by substantial lowering of κ and synergistic enhancement of the power factor. We perform first-principles density functional theory calculations to investigate the structure, stability, electronic structure, and transport properties of the synthesized alloy, which rationalize the reduction in the lattice thermal conductivity to the increase in anharmonicity due to the alloying. This study upholds the new possibilities of finding biphasic-quaternary HH compositions with intrinsically reduced κ for prospective thermoelectric applications.
本征晶格热导率高一直是在先进的三元半赫斯勒（HH）合金中实现高热电优值（ZT）的主要瓶颈。在这项工作中，我们报道了一种稳定的 n 型双相-四元（Ti,V）CoSb HH 合金，其晶格热导率κ≈2 W m K 在很宽的温度范围内（300-873 K），可与报道的纳米结构 HH 合金相媲美。在退火过程中由旋节分解驱动的固态相变被观察到，这显著增强了声子散射，而电性能与改变的电子能带结构和价电子数（VEC）很好地相关。通过显著降低κ和协同增强功率因子，在 873 K 时获得了约 0.4（±0.05）的最大 ZT。我们进行了第一性原理密度泛函理论计算，以研究合成合金的结构、稳定性、电子结构和输运性质，这将晶格热导率的降低解释为由于合金化导致的非谐性增加。这项研究为寻找具有本征低κ的双相-四元 HH 成分以用于有前景的热电应用提供了新的可能性。
