Large thermoelectric power factors by opening the band gap in semimetallic Heusler alloys

Abstract

Efficient thermoelectric devices are typically built from semiconducting materials since their band gap leads to an asymmetry in the continuum of energy-dependent charge transport necessary for a large Seebeck effect. Due to their low cost and excellent mechanical properties half- and full-Heusler compounds have emerged as promising candidates for various applications. Here, we demonstrate how the thermopower of semimetallic Fe2VAl-based Heusler alloys can be significantly increased by transferring electronic states from within the pseudogap to higher energies. Density functional theory calculations predict that partial Ti and Si co-substitution in Fe2V1−xTixAl1−ySiy drives an opening of the pseudogap, that can be likewise achieved in Fe2V1−xTaxAl1−ySiy. Consequently, our experimental measurements on these co-substituted systems reveal exceptionally large thermoelectric power factors (7.3 − 10.3 mWm−1K−2 near room temperature), as well as average power factors up to 4.6 mWm−1K−2 in the most pratical temperature range (293 − 573 K). With this work we set the course for a general and reliable way of boosting the thermoelectric performance of semimetallic Heusler alloys.