Collaborative effects of Zn and Sb Co-doping in magnesium silicide for thermoelectric applications

Abstract The effects of Zn and Sb co-doping in Mg 2 Si are investigated for thermoelectric applications, particularly focusing on the bonding with an Ni electrode and the grain boundaries. In the case of single Sb doping in Mg 2 Si, Sb is segregated at the interface with the Ni electrode, often accompanied by void formation due to the Kirkendall mechanism. On the other hand, in the case of Zn and Sb co-doping in Mg 2 Si, fast diffusion of Zn and the formation of a stable Zn-Sb alloy result in a smooth interface and void-free Zn-Sb-rich region embedded by the intermetallic ω-phase on the Mg 2 Si side of the interface with the Ni electrode. The thermoelectric properties and microanalyses at the grain boundaries with and without post-annealing reveal significant atomistic redistributions of Zn to form Zn-O segregation at the grain boundaries while keeping the Sb distribution uniform. Such Zn-O segregation possibly reduces the barrier height at the grain boundaries and stabilizes the grains compared to the case without post-annealing, where reactive oxygen remains. The long-term annealing test up to 1300 h under 773 K in air shows good stability of the materials with the Ni electrode. These collaborative effects will be particularly important for achieving reliable thermoelectric modules using Mg 2 Si.