Synergistically Optimizing Electrical and Thermal Transport Properties of ZrCoSb through Ru Doping

ZrCoSb is a promising p-type thermoelectric compound owing to its unique valence band structure, but the further improvement of its thermoelectric properties is constrained by less suitable dopants. In this work, we demonstrate that heavy element (ruthenium) doping at the 4c site allows simultaneous optimization of electrical transport properties and suppression of thermal conductivity. On the one hand, the replacement of Ru for Co results in valence band convergence by moving the Fermi level downward into the light Γ band, which significantly improves the electrical transport properties. On the other hand, the large difference in atomic size and mass between Ru and Co leads to strong strain field and mass fluctuation scattering, which remarkably reduces the lattice thermal conductivity. Consequently, a maximum thermoelectric figure of merit zT of 0.5 is achieved in ZrCo0.925Ru0.075Sb. This work highlights the promising effect of heavy-element doping at the 4c position on the thermoelectric performance of the p-type ZrCoSb compound.