Bismuth is the most common alloying element for high-performance Mg 3 Sb 2 -based thermoelectric compounds. However, the electrical and thermal transport data is lacking for undoped Mg 3 (Sb, Bi) 2 solid solutions. In this study, theoretical calculation results show that Bi alloying can reduce the band gap of Mg 3 Sb 2 , favoring the regulation of carrier concentration. Both Mg 3 Sb 2 and Mg 3 SbBi compounds present a single band structure on the valence band maximum at Γ of the Brillouin zone. Incorporating the Bi element can slightly increase the density of states (DOS) on the valence band maximum, which is beneficial for the Seebeck coefficient. Mg 3 Sb 2-x Bi x (0 � x � 0.8) compounds were experimentally prepared via ball milling (BM) combined with the spark plasma sintering (SPS) technique. The carrier concentration, electrical conductivity, and power factor of the samples tend to increase with the increasing Bi content. Bismuth alloying significantly reduces the total thermal conductivity in the low-temperature range, with the lowest value of 0.65 Wm À 1 K À 1 obtained at ~400 K for the x = 0.2 sample. The peak ZT value of 0.077 at 800 K and the average ZT of 0.051 in the temperature range of 450-800 K are obtained for the x = 0.2 sample, which is 93% and 219% higher than those of the unalloyed sample, respectively. This work reveals the Bi-alloying induced transport mechanism and provides fundamental thermoelectric data regarding the undoped Mg 3 Sb 2-x Bi x (0 � x � 0.8) solid solutions.

Grain boundary (GB) scattering has been widely reckoned as a primary restraint on room-temperature (RT) carrier mobility in Mg3Sb2-based materials. In this work, two-dimensional graphene (G) with varied contents was...