Continuously Enhanced Structural Disorder To Suppress the Lattice Thermal Conductivity of ZrNiSn-Based Half-Heusler Alloys by Multielement and Multisite Alloying with Very Low Hf Content

ZrNiSn-based half-Heusler (HH) alloys are considered very promising thermoelectric (TE) materials at intermediate and high temperatures due to their favorable intrinsic electrical properties, but they are also limited by their inherent high thermal conductivities. Numerous works have focused on reducing their thermal conductivities, especially their lattice thermal conductivities. A multielement (Ti, Hf, Nb, V, and Sb) and multisite alloying strategy for simultaneously improving the electrical properties and greatly reducing the lattice thermal conductivity of ZrNiSn-based HH TE materials is reported in this work. The continuous enhancement in structural disorder is the main factor in dramatically suppressing the lattice thermal conductivity of the materials. The use of suitable dopants also optimizes the electrical properties of the material, which is also an indispensable aspect in achieving high ZT values. As a consequence, a lowest lattice thermal conductivity κl = 0.99 W/(m K) and a highest ZT ∼ 1.2 were obtained for Zr0.95M0.05Ni1.04Sn0.99Sb0.01 (M = Ti0.25Hf0.25V0.25Nb0.25) refined by a ball-milling process. The calculated conversion efficiency (η) of the same sample from room temperature to 873 K was close to 12%. In addition, compared with that used in other studies, the amount of Hf used in this study was greatly reduced, which means a reduction in cost. All of the findings in this study make the commercialization of ZrNiSn-based TE materials more competitive.