Iron-based Semiconducting Half-Heusler Alloys for Thermoelectric Applications

Iron-based half-Heusler alloys constitute an emerging class of semiconducting intermetallics for scalable and efficient thermoelectric conversion, owing to their remarkably high-power factor, abundance, and low cost. This review encompasses the recent advances in materials synthesis and evolving aspects of optimization pathways in pre-existing Fe-based half-Heusler compositions for attaining a higher thermoelectric figure of merit (zT). The experimental outcomes and theoretical predictions were analyzed and compared using a parametric framework to understand the underlying electronic transport responsible for high power factors exhibited by most of these alloys distinctively. Alongside, effective microstructural approaches were reviewed for which favorable reduction in intrinsically high lattice thermal conductivity (kappa(L)) was attained. The electronic structures of MFeSb (M=V, Nb, and Ta) half-Heuslers is also analyzed using density functional theory-based calculations to understand the origin of favorable conduction and electrical transport properties. Finally, processing-structural-property correlations are discussed to highlight the relevance of structural ordering, phase transformation, and defects on transport properties, for developing effective strategies and material design in Fe-based half-Heuslers for their development in thermoelectrics.