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

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 elec-tronic performance and high thermal conductivity. Here, it is demonstrated that enhanced power factor of 46 mu W 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 pre-cipitates 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.