First-principles study of disordered half-Heusler alloys \textit{X}Fe$_{0.5}$Ni$_{0.5}$Sn (\textit{X} = Nb, Ta) as thermoelectric prospects

TL;DR

This study uses first-principles simulations to identify disordered half-Heusler alloys with low lattice thermal conductivity and enhanced thermoelectric efficiency, suggesting their potential for thermoelectric applications.

Contribution

The paper demonstrates that NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn alloys have lower thermal conductivity and higher ZT compared to traditional alloys, highlighting their promise for thermoelectric use.

Findings

NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn have lower lattice thermal conductivity.

Predicted 35 ext% and 17 ext% ZT enhancement over TiCoSb.

Optimal thermoelectric performance at 400-600 K and carrier concentration below 10$^{21}$ carriers/cm$^3$.

Abstract

High lattice thermal conductivity in half-Heusler alloys has been the major bottleneck in thermoelectric applications. Disordered half-Heusler alloys could be a plausible alternative to this predicament. In this paper, utilizing first-principles simulations, we have demonstrated the low lattice thermal conductivity in two such phases, NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn, in comparison to well-known half-Heusler alloy TiCoSb. We trace the low thermal conductivity to their short phonon lifetime, originating from the interaction among acoustic and low-lying optical phonons. We recommend nanostructuring as an effective route in further diminishing the lattice thermal conductivity. We further predict that these alloys can be best used in the temperature range 400-600~K and carrier concentration of less than 10$^{21}$ carriers cm$^{-3}$. We found $\sim$35\% and $\sim$17\% enhancement in $ZT$ for NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn, respectively, as compared to TiCoSb. We are optimistic of the findings and believe these materials would attract experimental investigations.