Enhancing the Thermoelectric Performance of n-Type Mg₃Sb₂-Based Materials via Ag Doping

The n-type Mg₃(Sb, Bi)₂ compounds show great potential for wasted heat energy harvesting due to their promising thermoelectric properties. This work discovers that doping transition element Ag into the n-type Mg₃(Sb, Bi)₂ can effectively optimize the power factor and suppress the lattice thermal conductivity simultaneously. Interestingly, the Ag doping has different effects compared to the isoelectronic and same group element Cu addition studied previously. A high power factor of 19.6 µW cm^-1 K^-2 is obtained at 673 K owing to the increased electrical conductivity. At the same time, the lattice thermal conductivity is reduced to ≈0.5 W m^-1 K^-1 because of enhanced phonon scattering induced by Ag atoms. These improvements lead to a peak figure of merit (ZT) of 1.64 at 673 K as well as a high average ZT of 1.27 is obtained from 323 K to 673 K. Furthermore, a thermoelectric single leg with a competitive conversion efficiency of ≈11% under a hot-side temperature of 673 K is fabricated successfully. In addition, a 2-pair module composed of n-type Mg₃(Sb, Bi)₂ alloy and p-type MgAgSb-based compound demonstrates the high conversion efficiency of ≈7.9% at a temperature difference of 277 K, which will significantly upgrade the sustainable energy recycling technology.