Synergistic Optimization of Electronic and Thermal Transport in Hf-Free ZrNiSn HH Alloy through WO₃ Compositing

Utilizing metal oxides to synergistically optimize electronic and thermal transport represents a rapidly growing field in research on half-Heusler (HH) thermoelectric materials. In this work, nanometer-sized WO3 powder was uniformly dispersed into the arc-melted ZrNiSn powder, and ZrNiSn/WO3 composites with varying concentrations were synthesized employing spark plasma sintering. The presence of secondary phases of ZrO2 and tungsten (W), identified in the microstructure analysis, not only enhances the electrical conductivity through electron injection but also increases the Seebeck coefficient by energy filtering effect. These multiphase microstructures generate defects to scatter more phonons and lead to suppression of lattice thermal conductivity up to ∼60% at 840 K. The highest thermoelectric figure of merit ZT of approximately 1.02 was achieved for 1.5 wt % WO3/ZrNiSn composite, which is among the highest reported for hafnium (Hf)-free ZrNiSn-based composites in the literature at 840 K. This enhancement in thermoelectric performance may be attributed to the enhanced carrier concentration and phonon scattering across multiple phase boundaries. Therefore, a decoupling in electronic and thermal transport properties has been achieved through multiple-phase structuring in Hf-free ZrNiSn HH alloy.