Comprehensive First-Principles Study of Structural, Electronic, Mechanical, Optical, and Thermoelectric Properties of Fe-Based Half-Heusler Compounds

This study presents a systematic first-principles investigation of Fe X Bi ( X = V, Nb, Ta) half-Heusler compounds, focusing on their structural, mechanical, electronic, optical, and thermoelectric (TE) properties. Density functional theory combined with Boltzmann transport theory is employed to explore their electronic structure and transport behavior. Structural optimization confirmed β-type ordering as the most stable configuration of the half-Heusler alloys. All compounds exhibit mechanical and dynamic stability, with high Debye temperatures and melting points, suggesting excellent thermal resilience. Band structure analysis reveals indirect band gaps increasing from the V to Ta substitution. Optical spectra indicate tunable dielectric responses across the NIR-UV range. TE analysis shows that FeTaBi is a viable candidate for high-temperature (∼1200 K) TE devices with a figure of merit, ZT ∼ 1. Meanwhile, FeVBi exhibits as a potential TE material in the midtemperature range (900 K), and high efficiency is observed both for the p- and n-type ( ZT ∼ 0.85 and 0.97, respectively) materials. The combined findings provide a comprehensive foundation for the advancement of Fe-based half-Heusler compounds in mid- to high-temperature TE applications.