Discovery of YbNiSb-Based Half-Heusler Alloys as Promising Thermoelectric Materials

Half-Heusler materials are promising candidates for high-temperature power generation and have relatively high lattice thermal conductivity compared to other thermoelectric material systems. In this work, we report novel p-type YbNiSb-based half-Heusler alloys with a low lattice thermal conductivity (similar to 3.6 W m-1 K-1 at 340 K) that resulted from their large Gru''neisen parameter, low sound speed, and low Debye temperature. All YbNiSb-based alloys exhibit a high carrier mobility of 30-50 cm2 V-1 s-1 at room temperature because of their relatively small effective mass. Importantly, the structural analysis reveals that Yb-rich Yb1.3Ni0.9Sb0.8 exhibits Yb/Ni and Yb/Sb substitution, indicating a wide homogeneity region of the YbNiSb phase experimentally. The adjustable Yb and Ni contents in YbNiSb-based alloys can modify the band structure around the Fermi level and significantly affect electrical transport properties. Additionally, by doping Ta at Yb sites, the carrier concentration and lattice thermal conductivity of these alloys can be manipulated. Consequently, a peak zT value of 0.45 at 823 K was achieved for Yb0.95Ta0.05NiSb. Our work demonstrates that YbNiSb-based alloys are promising p-type thermoelectric materials and suggests the possibility of exploring novel thermoelectric alloys in rare-earth nickel pnictides via tuning their composition and crystal structure.