The effect of Mg3As2 alloying on the thermoelectric properties of n-type Mg3(Sb, Bi)2

Abstract

Mg₃Sb₂–Mg₃Bi₂ alloys have been heavily studied as a competitive alternative to the state-of-the-art n-type Bi₂(Te,Se)₃ thermoelectric alloys. Using Mg₃As₂ alloying, we examine another dimension of exploration in Mg₃Sb₂–Mg₃Bi₂ alloys and the possibility of further improvement of thermoelectric performance was investigated. While the crystal structure of pure Mg₃As₂ is different from Mg₃Sb₂ and Mg₃Bi₂, at least 15% arsenic solubility on the anion site (Mg₃((Sb_0.5Bi_0.5)_1−xAs_x)₂: x = 0.15) was confirmed. Density functional theory calculations showed the possibility of band convergence by alloying Mg₃Sb₂–Mg₃Bi₂ with Mg₃As₂. Because of only a small detrimental effect on the charge carrier mobility compared to cation site substitution, the As 5% alloyed sample showed zT = 0.6–1.0 from 350 K to 600 K. This study shows that there is an even larger composition space to examine for the optimization of material properties by considering arsenic introduction into the Mg₃Sb₂–Mg₃Bi₂ system.