Synergistic Effect of Band and Nanostructure Engineering on the Boosted Thermoelectric Performance of n-Type Mg_(3+δ)(Sb, Bi)_2 Zintls

摘要

Thermoelectric Mg_(3+δ)(Sb, Bi)_2 Zintls have attracted significant attentionbecause of their high-performing, eco-friendly, and cost-effective features, buttheir thermoelectric properties still need improvement for application to practicaldevices. Here an outstanding ZT of ≈1.87 at 773 K and a high averageZT of ≈1.2 in n-type Y-doped Mg_(3.2)Sb_(1.5)Bi_(0.49)Se_(0.01) are reported, both of whichrank as top values among the reported literature. First-principles calculationsindicate that substituting the Mg site with Y shifts the Fermi level into theconduction band and simultaneously narrows the bandgap, both strengtheningthe n-type semiconducting feature and boosting the electron carrierdensity 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) isachieved at 773 K in Mg3.18Y0.02Sb1.5Bi0.49Se0.01, benefiting from the rationallytuned carrier density of ≈7.7 × 1019 cm~(-3) at this temperature. In addition,the doped Ys act as point defects to cause significant lattice distortions andstrains, confirmed by comprehensive micro/nanostructure characterizations.These lattice imperfections suppress the lattice thermal conductivityto ≈0.41 W m~(-1) K~(-1) at 773 K, leading to such a high ZT. Furthermore, a highenergy conversion efficiency of ≈13.8 is predicted by a temperature gradientof 450 K, indicating a great potential to be applied to practical devices formid-temperature applications.