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.

Typical 18-electron half-Heusler compounds, ZrNiSn and NbFeSb, have been identified as promising high temperature thermoelectric materials. NbCoSb with nominal 19 valence electrons, which is supposed to be metallic, has recently been reported to also exhibit thermoelectric properties of a heavily doped n-type semiconductor. Here we experimentally demonstrate, for the first time, that This article is protected by copyright. All rights reserved. 2 the nominal 19-electron NbCoSb is actually the composite of 18-electron Nb 0.8+ CoSb (0 ≤ < 0.05) and impurity phases. Single phase Nb 0.8+ CoSb with intrinsic Nb vacancies, following the 18-electron rule, possesses improved thermoelectric performance, and the slight change in the content of Nb vacancies has a profound effect on the thermoelectric properties. The carrier concentration can be controlled by varying the Nb deficiency, and the optimization of the thermoelectric properties can be realized within the narrow pure phase region. Benefiting from the elimination of impurity phases and the optimization of carrier concentration, thermoelectric performance is remarkably enhanced by ~100% and a maximum zT of 0.9 is achieved in Nb 0.83 CoSb at 1123 K. This work expands the family of half-Heusler thermoelectric materials and opens a new avenue for searching for nominal 19electron half-Heusler compounds with intrinsic vacancies as promising thermoelectric materials.

Bulk nanostructuring has been one of the leading strategies employed in the past decade for the optimization of thermoelectric properties by introducing strong grain boundary scattering of low-frequency phonons. However,...

Progress of utilizing conductive polymers and their composites to prepare flexible, smart and self-sustainable supercapacitors for portable/wearable electronics is reviewed.