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.