Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

Junjie Yu, Chenguang Fu, Yintu Liu, Kaiyang Xia, Umut Aydemir, Thomas C. Chasapis, G. Jeffrey Snyder, Xinbing Zhao*, Tiejun Zhu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

151 Scopus citations


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.

Original languageEnglish (US)
Article number1701313
JournalAdvanced Energy Materials
Issue number1
StatePublished - Jan 5 2018


  • half-Heusler compounds
  • solid solutions
  • thermal conductivity
  • thermoelectric materials

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)


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