Synchronously enhanced thermoelectric and mechanical properties of Ti doped NbFeSb based half-heusler alloys by carrier regulation and phonon engineering

Abstract

NbFeSb based half-heusler thermoelectric materials have great potential in high-temperature energy harvesting. However, their conversion efficiency is limited by the low figure of merit zT, which is attributed to poor electronic performance and high thermal conductivity. Here, it is demonstrated that enhanced power factor of 46 μW cm−1 K−2 and zT value of 0.9 at 973 K is achieved in spark plasma sintered Nb0.8Ti0.2FeSb. It is depicted that a tremendous increase in the hole concentration owing to Ti substitution, results in a significant promotion of electrical performances. In addition, numerous phonon scattering centers, such as point-defects, nano precipitates as well as electro-acoustic coupling, collectively suppress the lattice thermal conductivity from 7.4 W m−1 K−1 to 3.3 W m−1 K−1 at 973 K. Furthermore, NbFeSb based alloys exhibit excellent mechanical property and the Vickers hardness reaches 10.8 GPa, which would be beneficial for TE devices fabrication.