Effect of Off-Stoichiometry and Point Defects on Thermoelectric Properties of a W‑Substituted Fe2VAl Heusler Compound

Fe2VAl-based Heusler thermoelectric materials are attractive for power supplies used in practical applications to drive Internet of things (IoT) devices using low-temperature waste heat at temperatures of less than 500 K. In this paper, we present a simple method to introduce point defects and disorder at Fe/V sites via W substitution to enhance the thermoelectric performance of Fe2–x W x VAl (x = 0, 0.05, 0.1, and 0.15) samples. We obtained a relatively high dimensionless figure of merit zT of 0.28 at 423 K for the samples with x = 0.05 and 0.1. Although both samples had the same maximum zT value, the sample with x = 0.05 showed a power factor of 4.7 mW m–1 K–2 at 423 K, which was higher than that (3.7 mW m–1 K–2 at 423 K) of the sample with x = 0.1. In addition, the thermal conductivity of 7.1 W m–1 K–1 at 423 K of the sample with x = 0.05 was higher than that (5.7 W m–1 K–1 at 423 K) of the sample with x = 0.1. We confirmed that the synthesized sample with x = 0.05 showed excellent thermal durability that allowed it to maintain almost constant electrical resistivity and Seebeck coefficient for 10,000 min; this was confirmed by exposure tests performed at 423 and 573 K. The current simple fabrication process, which uses a combination of melting and sintering methods, will be attractive for mass production of the W-substituted Fe2VAl-based Heusler compound with the relatively high zT of 0.28.