High-Performance n-Type Mg3Sb2-Based Thermoelectrics via Mn Doping and Mg Compensation

Abstract

The n-type Mg3Sb2-based thermoelectric materials show great potential in waste heat recovery. However, Mg loss during high-temperature processing induces donor-type defects that strengthen ionized impurity scattering (IIS) and force a trade-off between electrical and thermal properties. To overcome this bottleneck, this work proposes a synergistic regulation strategy: “transition metal solid solution + intrinsic defect compensation”. The effects of Mn doping and excessive Mg compensation on the structure and physical properties of Mg3.9–xMnx(Sb0.75Bi0.25)1.99Te0.01 (x = 0.01–0.07) were systematically studied by vacuum melting combined with spark plasma sintering (SPS) technology. The results show that the successful replacement of Mg sites by Mn with x = 0.03 can suppress donor-type defects and weaken IIS, so that the carrier mobility at room temperature increases sharply to 101.67 cm2·V–1·s–1, nearly five times higher than that of the undoped matrix. Meanwhile, Mn-induced mass fluctuation and lattice distortion create strong scattering centers for mid-high frequency phonons, suppressing lattice thermal conductivity to 0.38–0.65 W·m–1·K–1. On this basis, precise control of Mg compensation (14 wt %) effectively fills volatilization vacancies and maintains a highly dense microstructure, achieving a balance between high carrier mobility and ultra-low thermal conductivity. Finally, the optimized sample obtained a power factor of 1.9 × 10–3 W·m–1·K–2 at 373 K, and achieved a peak thermoelectric figure of merit ZT = 1.38 at 723 K. This work reveals the physical mechanism of electrical-thermal transport under the coupling of multiple defects and provides a reference for the microstructure design of high-performance Zintl-phase thermoelectric materials.