Thermoelectric performance of Ni-Au metallic alloys determined by resonant scattering

This work presents a theoretical study of the electronic structure and transport properties of $\mathrm{Ni}$-$\mathrm{Au}$ alloys, recently identified as excellent thermoelectric metals with a power factor significantly exceeding that of conventional semiconductor thermoelectrics. Using first-principles calculations based on the Korringa-Kohn-Rostoker method combined with the coherent-potential approximation and the Kubo-Greenwood formalism, we demonstrate the key role of resonant scattering in determining the thermoelectric properties of these alloys. This is supported by calculated densities of states, Bloch spectral functions, electrical conductivity, and thermopower. Alloying $\mathrm{Ni}$ with $\mathrm{Au}$ not only induces resonant scattering but also leads to the formation of a flat band below the Fermi level. The combination of these two features results in high thermopower arising from a transition from resonant to weak scattering regimes near the Fermi level. Our findings are further compared with analogous calculations for constantan, a $\mathrm{Ni}$-$\mathrm{Cu}$ alloy long regarded as a reference thermoelectric metal. We show the key differences between the $\mathrm{Ni}$-$\mathrm{Au}$ and $\mathrm{Ni}$-$\mathrm{Cu}$ systems that explain why $\mathrm{Ni}$-$\mathrm{Au}$ exhibits nearly twice the thermopower of $\mathrm{Ni}$-$\mathrm{Cu}$. Finally, we simulate the effect of lattice parameter variation on the thermoelectric performance of $\mathrm{Ni}$-$\mathrm{Au}$ and suggest that this is a promising pathway for further enhancement, for example, through additional alloying or layer deposition.