Enhanced power factor by transition metal substitution in the thermoelectric Kagome metal Ni₃Sn

Metallic thermoelectric materials offer promise in terms of elemental abundance and avoiding rare or toxic elements. Here, we demonstrate that substitution of Co in the Kagome metal Ni₃Sn leads to an enhanced Seebeck effect (S _max = -55 µV K^-1), which supports a promising thermoelectric power factor, PF = 5 mW m^-1 K^-2 and figure of merit, zT = 0.1. Density Functional Theory calculations show that the metallic electronic structure consists of dispersive bands around the Fermi level (E _F) and a combination of flattened out and dispersive bands below it. Boltzmann transport equation modelling shows that the resulting step-change increase in density of states (DOS) from the flattened bands, leads to the large observed S values through selective carrier scattering. With Co substitution, the alignment of E _F to the high DOS region is improved, enhancing S. Substitution with Cu moves E _F away from the high DOS region, reducing S. This work shows that the behaviour of Ni₃Sn can be understood by DOS scattering driven carrier filtering. As also proposed by Mott, this is a robust effect that occurs in degenerate metallic conditions, leading to more than two times enhancement in S and applies to many more intermetallic materials with an appropriately tuned band structure.