Synergistic Optimization of the Thermoelectric Transport Properties of Mg3Sb2 through Dy/Tm Doping Combined with S Compensation Strategy

Mg₃Sb₂-based thermoelectric materials have attracted considerable attention for medium-temperature applications owing to their low cost and excellent charge carrier transport properties. In this work, a cooperative approach combining lanthanide doping (Dy and Tm) with trace sulfur compensation was employed to effectively modulate the electron–phonon structure of Mg₃Sb₂, thereby enhancing its thermoelectric performance. First-principles computational analyses demonstrate that the synergistic incorporation of S, Dy, and Tm effectively modulates the electronic band structure. The Fermi level is upshifted into the conduction band, while multiple flat bands form near the conduction band minimum. This dual modulation effect facilitates band convergence and narrows the bandgap, thereby improving n-type charge transport. Additionally, phonon transport simulations demonstrate that Dy and Tm effectively suppress phonon propagation, thereby reducing the lattice thermal conductivity. Through collaborative optimization, the Tm_0.03Mg_3.17Sb_1.5Bi_0.49S_0.01 composition reaches a maximum ZT of 1.4 at 723 K. Finite element simulations predict that thermoelectric modules based on this composition could reach a maximum energy conversion efficiency exceeding 9% in a single-leg configuration. These findings confirm that Dy and Tm act as highly effective n-type dopants, enabling concurrent optimization of both electron and phonon transport in Mg₃Sb₂, thus presenting substantial promise for practical applications in medium-temperature waste heat recovery.