Atomic Disorder Engineering of N-Type Thermoelectric Fe₂VAl Approaching the ZT of Bi₂Te₃

The L2₁ intermetallic compound Fe₂VAl is an ecofriendly, low cost, and easy to process potential replacement for conventional low temperature (250 - 500 K) thermoelectric materials used for waste-heat energy harvesting, such as Bi₂Te₃, which is brittle and uses toxic and expensive elements. The main issue with Fe₂VAl is its high thermal conductivity (~25 W/mK at 300 K). The aim of this project is to identify dopants and engineer atomic disorder to enhance both the thermal and electrical properties of bulk n-type Fe₂VAl.<br/>While the highly ordered L2₁ phase is the ground state, the higher temperature B2 (Al-V site swapping) and A2 (fully disordered) phases, whose transition temperatures are identified using DSC, can be retained through quenching. With the addition of Ge, these meta-stable phases, which are quantified using XRD, can be further stabilized. The band structures of the disordered phases show a flattening of the conduction band and therefore an increased effective carrier mass and reduced mobility which is compensated for by the increased carrier density. The result is a high Seebeck coefficient approaching 200 µV/k at 350 K. With reduced lattice periodicity from large element doping and disordered phases, the temperature dependent thermal conductivity shows “glass-behavior” and is reduced by &gt;80% to below 5 W/mK. The net result is a figure of merit, ZT, &gt;0.7 at 400 K, twice the value previously reported and rivaling the performance of Bi₂Te₃ (maximal ZT ~0.9).