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

TL;DR

This study uses first principles calculations to analyze the electronic structure of Fe₂V₀.₈W₀.₂Al thin films, revealing ferromagnetic metallic behavior and challenging previous explanations for their high thermoelectric figure of merit.

Contribution

It provides the first detailed electronic structure analysis of disordered Fe₂V₀.₈W₀.₂Al thin films, contradicting earlier pseudo-gap hypotheses for their high ZT.

Findings

Fe₂V₀.₈W₀.₂Al is a ferromagnetic metal at 0 K.

The Seebeck coefficient at 400 K is small (<30 μV/K).

No deep pseudo-gap at the Fermi level is observed.

Abstract

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.