Engineering the Thermoelectric Transport in Half-Heusler Materials through a Bottom-Up Nanostructure Synthesis

Half-Heusler (HH) alloys are among the best promising thermoelectric (TE) materials applicable for the middle-to-high temperature power generation. Despite of the large thermoelectric power factor and decent figure-of-merit ZT (≈1), their broad applications and enhancement on TE performance are limited by the high intrinsic lattice thermal conductivity (κ_L) due to insufficiencies of phonon scattering mechanisms, and the fewer powerful strategies associated with the microstructural engineering for HH materials. This study reports a bottom-up nanostructure synthesis approach for these HH materials based on the displacement reaction between metal chlorides/bromides and magnesium (or lithium), followed by vacuum-assisted spark plasma sintering process. The samples are featured with dense dislocation arrays at the grain boundaries, leading to a minimum κ_L of ≈1 W m⁻¹ K⁻¹ at 900 K and one of the highest ZT (≈1) and predicted η (≈11%) for n-type Hf_0.25Zr_0.75NiSn_0.97Sb_0.03. Further manipulation on the dislocation defects at the grain boundaries of p-type Nb_0.8Ti_0.2FeSb leads to enhanced maximum power factor of 47 × 10⁻⁴ W m⁻¹ K⁻² and the predicted η of ≈7.5%. Moreover, vanadium substitution in FeNb_0.56V_0.24Ti_0.2Sb significantly promotes the η to ≈11%. This strategy can be extended to a broad range of advanced alloys and compounds for improved properties.