Unexpected band gap increase in the Fe2VAl Heusler compound. (June 2020) - Berche, A.
Abstract: Knowing the electronic structure of a material is essential in energy applications to rationalize its performance and propose alternatives. Materials for thermoelectric applications are generally small-gap semiconductors and should have a high figure of merit, known as ZT. Even if the Fe2 VAl Heusler compound has a decent ZT, its conductive nature (semimetal or semiconductor) is not yet clarified especially at low temperature. In this article, we focus our density functional theory (DFT) calculations on the effect of temperature on the bandgap of Fe2 VAl. In contrast to what is usually observed, we show that both the temperature increase and the formation of thermally activated Al/V inversion defects (observed experimentally) open the bandgap. Such an unusual behavior is the key for reconciling all bandgap measurements performed on the Fe2 VAl compound using a standard generalized gradient approximation functional and could be an efficient way for improving the thermoelectric properties of this family of materials. Graphical abstract: Image 1 Highlights: The bandgap of Fe2 VAl increases with increasing temperatures due to electron-phonon interactions. In the stoichiometric Fe2 VAl compound, Al and V can exchange their position with increasing temperature. With increasing defect concentration, antiphase inclusions will form. Within generalized gradient approximation, Al/V inversions open the bandgap from a semimetal (at 0 K) to a semiconductor (at high temperature). This numerical study reconciles all the available experimental measurements.