Tuning of the electronic and phononic properties of NbFeSb half-Heusler compound by Sn/Hf co-doping.

Pure phase NbFeSb 1-x Sn x (where x = 0, 0.04, 0.08, 0.12, 0.16) half-Heusler samples were prepared by direct mechanical alloying followed by spark plasma sintering. The results showed that the substitution of Sb by Sn can effectively enhance the peak figure of merit (ZT) to 0.55 at 923 K in NbFeSb 0.88 Sn 0.12 through optimized carrier concentration. To further reduce the lattice thermal conductivity (κ L), we substituted Nb by Hf to enhance the point defect scattering of phonon transport. A maximum reduction of ~80% in κ L was observed in Nb 0.8 Hf 0.2 FeSb 0.88 Sn 0.12 when compared to undoped NbFeSb at 573 K. We realized a minimum κ L of ~2.96 W m−1 K−1 at 673 K and a peak ZT of ~0.82 at 973 K for Nb 0.88 Hf 0.12 FeSb 0.88 Sn 0.12. Image, graphical abstract [ABSTRACT FROM AUTHOR]