Hinterleitner et al. have recently reported an exceptionally large ZT of 6 at 380 K in a Fe2V0.8W0.2Al thin film (Hinterleitner et al., Nature 576 (2019) 85, 10.1038 / s41586-019-1751-9).

ZT = 6 is nearly two orders of magnitude larger than in Fe2V0.9W0.1Al synthesized in bulk form (ZT = 0.1 at 350K). This very large dimensionless figure of merit would arise from a large Seebeck coefficient S = – 550 µV K-1 measured at 400 K. To justify theoretically their experimental results, Hinterleitner et al. calculated the electronic structure of thin film Fe2V0.8W0.2Al and found that it would be a semi-metal. However, they made use of a crystal structure that is not correct. To assess the theoretical scenario invoked by Hinterleitner et al. to justify their large ZT, we re-calculated the electronic structure, making use of the adequate crystal structure.

Calculated density of states in thin film Fe2V0.8W0.2Al, showing its metallic state, Seebeck coefficient calculated (400K) as a function of the chemical potential

Our calculations indicate that this material is a ferromagnetic metal at 0 K, displaying a Seebeck coefficient that cannot exceed ± 30 µV K-1 at 400 K. The theoretical scenario invoked by Hinterleitner et al. to explain their ZT = 6 should hence be fully reconsidered. Finally, our work also raises questions about their experimental results and could improve the awareness of experimentalists envisaging new research on the thermoelectric properties of thin film Fe2V0.8W0.2Al.

https://doi.org/10.1039/D0CP03738A