Field-assisted sintering process and part characterisation of hafnium-free half Heusler thermoelectric material ZrNiSn

Half-Heusler (HH) compounds have emerged as promising thermoelectric materials due to their excellent thermal stability, mechanical robustness, and environmentally friendly composition. In this study, we investigated a hafnium-free ZrNiSn-based half-Heusler compound, (Zr0.4Ti0.6)0.33Ni0.33(Sn0.98Sb0.02)0.33, synthesised through field-assisted sintering technology (FAST). This composition is developed to eliminate rare earth elements and costly hafnium while maintaining desirable thermoelectric properties. A systematic investigation of FAST processing parameters was conducted using factorial analysis, which revealed temperature as the most critical sintering parameter, followed by pressure, holding time, and heating rate. The FAST process has demonstrated excellent densification outcomes, achieving relative densities of up to 97.73%. Comprehensive characterisation of the optimised material showed a peak figure of merit (ZT) of 0.54 at 527 °C., with an average ZT value of 0.35 in the temperature range of 100–500 °C. This study demonstrates the potential of FAST in producing thermoelectric materials. It provides valuable insights into the relationship between processing parameters and material performance, contributing to developing sustainable and cost-effective materials for waste heat recovery applications.