Simultaneous optimization of thermoelectric and mechanical properties in p-type NbFeSb via entropy engineering

Abstract

NbFeSb-based half-Heusler (HH) alloys have drawn significant interest for their potential as thermoelectric (TE) materials due to their high-temperature stability and substantial potential for power generation. Nevertheless, their practical application remains limited by relatively low electrical conductivity (σ) and high intrinsic lattice thermal conductivity (κ _L ). Herein, we employ entropy engineering in the design of Nb _1-x M _x FeSb _0.98 Sn _0.02 (x = 0.09, 0.12, 0.15, and 0.18; M denotes Ti, Zr, and Hf in equimolar proportions). Specifically, multi-element doping boosts σ by approximately several orders of magnitude, yielding an excellent peak power factor (PF) of ~58.7 μW cm ^-1 K ^-2 for Nb _0.91 M _0.09 FeSb _0.98 Sn _0.02 at 373 K. Entropy-driven multi-scale defects act as efficient phonon scatterers, leading to a low κ L of ~3.1 W m ^-1 K ^-1 for Nb _0.82 M _0.18 FeSb _0.98 Sn _0.02 at 923 K. Combined with its enhanced PF of ~31.9 μW cm ^-1 K ^-2 , a peak TE figure of merit (zT) of ~0.52 is achieved for Nb _0.82 M _0.18 FeSb _0.98 Sn _0.02 medium-entropy HH alloy at 923 K. Meanwhile, solid solution strengthening and grain refinement yield a high Vickers hardness of ~1118 HV for Nb _0.82 M _0.18 FeSb _0.98 Sn _0.02 . This work demonstrates entropy engineering as an effective strategy for the synergistic optimization of TE and mechanical properties of NbFeSb-based HH alloys, advancing their prospects for practical power generation from waste heat.