Enhancing the thermoelectric performance of a Ti2FeNiSb2 double half-Heusler alloy through excess Ni-induced full-Heusler nanoprecipitates

Abstract

Double half-Heuslers (DHHs) have emerged as promising candidates for thermoelectric power generation at mid-high temperatures due to their exceptional chemical and mechanical stability, as well as high electronic transport properties. However, their limited thermoelectric conversion efficiency (ZT) has hindered their practical application. In the present study, we propose an approach to enhance the ZT of DHHs by generating full-Heusler (FH) nanoprecipitates through a simple and scalable compositional tuning method. We investigate the effectiveness of this approach using Ti₂FeNiSb₂ as a model system. Our results reveal that FH nanoprecipitates can substantially intensify the phonon scattering in Ti₂FeNiSb₂, leading to an ultra-low lattice thermal conductivity of ∼0.9 W m⁻¹ K⁻¹ at 973 K. Additionally, filtering of low-energy carriers, in the presence of FH nanoprecipitates, further improves the electronic transport properties. As a result, we achieved a relatively high zT of 0.31 in Ti₂FeNi_1.05Sb₂, which is 1.5-fold enhancement compared to the pristine Ti₂FeNiSb₂. These findings offer attractive opportunities for designing and developing high-performance DHH-based thermoelectric materials.