Regulating Ionized Impurity Scattering to Optimize Thermoelectric Performance in Zn-Doped n-Type Mg3(Sb,Bi)2

Abstract

Mg₃Sb₂ Zintl compounds have emerged as promising thermoelectric materials due to their favorable electronic structures and low lattice thermal conductivity. However, strong carrier scattering, including ionized impurity and grain boundary scattering, suppresses mobility and limits the power factor. This study reveals that Zn doping plays a crucial role in tuning carrier scattering mechanisms in n-type Mg₃(Sb,Bi)₂. The substitution of Mg with Zn weakens ionized impurity scattering, facilitating charge transport and increasing carrier mobility from ∼72 to ∼135 cm² V^–1 s^–1. As a result, a high power factor of ∼2089 μW m^–1 K^–2 is achieved at 573 K in Mg_3.155Zn_0.045Sb_1.5Bi_0.49Te_0.01. Furthermore, Zn incorporation introduces localized lattice distortions and promotes the formation of high-density dislocations, which intensify phonon scattering and significantly suppress lattice thermal conductivity to ∼0.54 W m^–1 K^–1 at 773 K. These synergistic enhancements contribute to an optimized thermoelectric performance, yielding a peak ZT of 1.71 at 773 K and an average ZT of 1.21. The estimated conversion efficiency reaches 13% under a 470 K temperature gradient, highlighting Zn doping as an effective strategy for advancing Mg₃(Sb,Bi)₂-based thermoelectric materials toward high-temperature energy harvesting applications.