On the structure and electronic properties of Fe$_2$V$_{0.8}$W$_{0.2}$Al thin films.

A very large thermoelectric figure of merit ZT = 6 at 380 K has recently been reported in Fe$_2$V$_{0.8}$W$_{0.2}$Al under thin-film form (Hinterleitner et al., Nature 576 (2019) 85). Under this form, Fe$_2$V$_{0.8}$W$_{0.2}$Al experimentally crystallizes in a disordered A2 crystal structure, different from its bulk-form structure (L21). First principles calculations of the electronic structure performed in A2-Fe$_2$V$_{0.8}$W$_{0.2}$Al supercells generated by the Special Quasi-random Structure (SQS) method are thus reported here. These calculations unambiguously indicate that A2-Fe$_2$V$_{0.8}$W$_{0.2}$Al is a ferromagnetic metal at 0 K, displaying a small Seebeck coefficient at 400 K (< 30 microV/K). The present results contradict the scenario of the occurrence of a deep pseudo-gap at the Fermi level, previously invoked to justify ZT = 6 in Fe$_2$V$_{0.8}$W$_{0.2}$Al thin films.