Efficient lanthanide Gd doping promoting the thermoelectric performance of Mg3Sb2-based materials

Abstract

Mg₃Sb₂-based thermoelectric materials have recently received heightened attention due to their diverse merits of high band degeneracy, ultralow lattice thermal conductivity and high carrier mobility. However, the inherently low carrier concentration of pristine Mg₃Sb₂ seriously hinders the advancement of this material toward high thermoelectric performance. Therefore, searching for proper dopants to optimize the carrier concentration is one of the primary avenues to realize superior thermoelectric performance in Mg₃Sb₂-based materials. Herein, by considering the electronegativity difference Δχ and mass difference ΔM between the dopant and host elements, we theoretically and experimentally demonstrate lanthanide Gd as an effective dopant to tune the carrier concentration of Mg₃Sb_1.3Bi_0.7 alloys. Owing to its high doping efficiency, a large carrier concentration up to 8.9 × 10¹⁹ cm⁻³ is realized through Gd doping, which is close to the optimal value. Moreover, the coarse grain size commendably mitigates the grain boundary effects and thus ensures high carrier mobility. Combining the greatly suppressed lattice thermal conductivity by point defect scattering, a maximum zT of 1.55 is achieved at 700 K in Mg_3.065Sb_1.3Bi_0.7Gd_0.015.