Designing high-performance n-type Mg3Sb2-based thermoelectric materials through forming solid solutions and biaxial strain

Abstract

N-type Mg₃Sb₂-based Zintl compounds with multi-valley conduction bands and low thermal conductivity exhibit high thermoelectric performance. Here, two strategies based on a solid solution map and biaxial strain engineering are investigated for the optimization of thermoelectric performance by using the first-principles method and Boltzmann transport theory. In Mg₃(Sb,Bi)₂ solid solution, increasing the Bi content leads to a decreased Seebeck coefficient and increased carrier mobility due to the changes in the electronic structure, which indicates that the optimal Bi content is urgently needed for the best electronic transport. The decreasing lattice thermal conductivity is mainly ascribed to the changes in the Grüneisen parameter and Debye temperature. The maximum ZT of Mg₃SbBi with an optimal carrier concentration of 3.38 × 10²⁰ cm⁻³ at 725 K can be up to 2.75 or even higher when the thermal conductivity decreases from the experimental value through its low bound value. Additionally, biaxial strain engineering is also effective in the enhancement of the thermoelectric performance.