Near room temperature thermoelectric performance improvement for Mg2Sn

Abstract

Mg₂Sn is a promising medium-temperature thermoelectric material due to its superior performance and non-toxic, low-cost nature. Because of the divergence of band effective mass and degeneracy between the conduction and valence band, Mg₂Sn is also promising to achieve superior performance near room temperature. To realize the desired bandgap and optimal carrier concentration, in this work, Mg₂Pb is alloyed to reduce the bandgap of Mg₂Sn, and Bi is adopted for carrier concentration optimization. Alloying with Mg₂Pb makes the bandgap gradually tuned, and with the increase in carrier concentration, more conduction band valleys are involved for electronic transport as the Fermi level goes deeper. Besides, the phonon scattering is simultaneously enhanced because of the introduced large number of defects. Finally, a power factor as high as 52 μW cm⁻¹ K⁻² at 400 K, and 42 μW cm⁻¹ K⁻² at room temperature is obtained in this work, and the peak zT value for the Mg_2.03Sn_0.734Pb_0.25Bi_0.016 sample reaches 0.8 at 500 K, the average figure of merit is zT_ave ∼ 0.6 within the temperature range of 300–550 K, surpassing many Mg₂Sn based materials near room temperature. The thermoelectric figure of merit can achieve a higher value if the lattice thermal conductivity is further reduced, which demonstrates that Mg₂Sn is promising for near room temperature applications.