Enhancing Thermoelectric Performances of Hf-Free ZrNiSn-Based Half-Heusler Alloys by Multisite Element Modulation

Hf alloying at the Zr site is an effective method to suppress the lattice thermal conductivity (κl) toward high thermoelectric (TE) performance for ZrNiSn-based half-Heusler TE materials. However, the high cost of the Hf element limits its large-scale application. Herein, we propose the multisite element modulation strategy for enhancing TE performances. At the initial stage, Nb–Ni codoping shifts the Fermi level into the conduction band, and the power factor increases by 25.3% over the pristine ZrNiSn. Subsequently, Ge–Si codoping induces multiscale defects such as point defects, dislocations, and nanoprecipitates to reduce the κl. Benefit from the comprehensive optimization of the electric-thermal properties, Zr0.96Nb0.04Ni1.04Sn0.95Ge0.025Si0.025 obtains a figure of merit (zT) of ∼0.78 at 923 K, representing a 29.6% improvement, compared to that of pristine ZrNiSn. Furthermore, due to the solid-solution strengthening and the grain refinement, the Vickers hardness of the ZrNiSn-based half-Heusler alloys (HHs) is further enhanced as well. This work achieves the collaborative optimization of the TE and mechanical performances of TE materials, proposing a new strategy for the development of Hf-free ZrNiSn-based HHs.