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((Sb0.5Bi0.5)1-xAsx)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.