Synergistic Effect of Band and Nanostructure Engineering on the Boosted Thermoelectric Performance of n‐Type Mg₃₊<i>_δ</i>(Sb, Bi)₂ Zintls

Abstract

Abstract Thermoelectric Mg 3+ δ (Sb, Bi) 2 Zintls have attracted significant attention because of their high‐performing, eco‐friendly, and cost‐effective features, but their thermoelectric properties still need improvement for application to practical devices. Here an outstanding ZT of ≈1.87 at 773 K and a high average ZT of ≈1.2 in n‐type Y‐doped Mg 3.2 Sb 1.5 Bi 0.49 Se 0.01 are reported, both of which rank as top values among the reported literature. First‐principles calculations indicate that substituting the Mg site with Y shifts the Fermi level into the conduction band and simultaneously narrows the bandgap, both strengthening the n‐type semiconducting feature and boosting the electron carrier density of Mg 3.2 Sb 1.5 Bi 0.49 Se 0.01 . A high power factor of ≈21.4 µW cm –1 K –2 is achieved at 773 K in Mg 3.18 Y 0.02 Sb 1.5 Bi 0.49 Se 0.01 , benefiting from the rationally tuned carrier density of ≈7.7 × 10 19 cm –3 at this temperature. In addition, the doped Ys act as point defects to cause significant lattice distortions and strains, confirmed by comprehensive micro/nanostructure characterizations. These lattice imperfections suppress the lattice thermal conductivity to ≈0.41 W m –1 K –1 at 773 K, leading to such a high ZT . Furthermore, a high energy conversion efficiency of ≈13.8% is predicted by a temperature gradient of 450 K, indicating a great potential to be applied to practical devices for mid‐temperature applications.