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Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials
Advanced Energy Materials ( IF 24.4 ) Pub Date : 2017-09-07 , DOI: 10.1002/aenm.201701313 Junjie Yu 1 , Chenguang Fu 1 , Yintu Liu 1 , Kaiyang Xia 1 , Umut Aydemir 2 , Thomas C. Chasapis 2 , G. Jeffrey Snyder 2 , Xinbing Zhao 1 , Tiejun Zhu 1
Advanced Energy Materials ( IF 24.4 ) Pub Date : 2017-09-07 , DOI: 10.1002/aenm.201701313 Junjie Yu 1 , Chenguang Fu 1 , Yintu Liu 1 , Kaiyang Xia 1 , Umut Aydemir 2 , Thomas C. Chasapis 2 , G. Jeffrey Snyder 2 , Xinbing Zhao 1 , Tiejun Zhu 1
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NbFeSb‐based half‐Heusler alloys have been recently identified as promising high‐temperature thermoelectric materials with a figure of merit zT > 1, but their thermal conductivity is still relatively high. Alloying Ta at the Nb site would be highly desirable because the large mass fluctuation between them could effectively scatter phonons and reduce the lattice thermal conductivity. However, practically it is a great challenge due to the high melting point of refractory Ta. Here, the successful synthesis of Ta‐alloyed (Nb1−xTax)0.8Ti0.2FeSb (x = 0 – 0.4) solid solutions with significantly reduced thermal conductivity by levitation melting is reported. Because of the similar atomic sizes and chemistry of Nb and Ta, the solid solutions exhibit almost unaltered electrical properties. As a result, an overall zT enhancement from 300 to 1200 K is realized in the single‐phase Ta‐alloyed solid solutions, and the compounds with x = 0.36 and 0.4 reach a maximum zT of 1.6 at 1200 K. This work also highlights that the isoelectronic substitution by atoms with similar size and chemical nature but large mass difference should reduce the lattice thermal conductivity but maintain good electrical properties in thermoelectric materials, which can be a guide for optimizing the figure of merit by alloying.
中文翻译：
难熔钽合金在提高NbFeSb热电材料品质因数中的独特作用
基于NbFeSb的半霍斯勒合金最近被认为是具有前景的高温热电材料，其品质因数zT > 1，但其导热系数仍然相对较高。非常希望在Nb处合金化Ta，因为它们之间的大质量波动会有效地分散声子并降低晶格热导率。然而，由于耐火材料Ta的高熔点，实际上是很大的挑战。在这里，成功合成了钽合金（Nb 1 - x Ta x）0.8 Ti 0.2 FeSb（x= 0 – 0.4）据报道，由于悬浮熔化而使导热率大大降低的固溶体。由于Nb和Ta的原子大小和化学性质相似，因此固溶体的电性能几乎保持不变。结果，单相Ta合金固溶体将zT从300 K提升到1200 K，x = 0.36和0.4的化合物在1200 K时最大zT为1.6。用具有相似大小和化学性质但质量差异大的原子进行等电子取代，应降低晶格的热导率，但在热电材料中保持良好的电性能，这可以作为合金化优化品质因数的指南。
更新日期：2017-09-07
中文翻译：
难熔钽合金在提高NbFeSb热电材料品质因数中的独特作用
基于NbFeSb的半霍斯勒合金最近被认为是具有前景的高温热电材料，其品质因数zT > 1，但其导热系数仍然相对较高。非常希望在Nb处合金化Ta，因为它们之间的大质量波动会有效地分散声子并降低晶格热导率。然而，由于耐火材料Ta的高熔点，实际上是很大的挑战。在这里，成功合成了钽合金（Nb 1 - x Ta x）0.8 Ti 0.2 FeSb（x= 0 – 0.4）据报道，由于悬浮熔化而使导热率大大降低的固溶体。由于Nb和Ta的原子大小和化学性质相似，因此固溶体的电性能几乎保持不变。结果，单相Ta合金固溶体将zT从300 K提升到1200 K，x = 0.36和0.4的化合物在1200 K时最大zT为1.6。用具有相似大小和化学性质但质量差异大的原子进行等电子取代，应降低晶格的热导率，但在热电材料中保持良好的电性能，这可以作为合金化优化品质因数的指南。
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