Effect of Sb/Bi doping sites on electronic structure and transport properties of Mg₂Si_0.375Sn_0.625 alloy from first-principles calculations

Defect formation energy, electronic structures, and transport properties of Sb/Bi-doped Mg₂Si_0.375Sn_0.625 alloys were successfully determined by first-principles calculations. Si sites in these alloys were preferentially substituted by Sb and Bi atoms. At the same doping content, Sb atoms provided larger carrier effective mass and lower electron concentration compared with Bi atoms. Correspondingly, the maximum Seebeck coefficient and power factor value of Mg₂Si_0.365Sn_0.625Sb_0.01 alloy were −260 μVK⁻¹ and 5.53 mWm⁻¹ K⁻¹, respectively. The highest electrical conductivity value of 1620 Scm⁻¹ was achieved with Mg₂Si_0.375Sn_0.615Bi_0.01 alloy, due to higher electron concentration supplied by its Bi atoms. Experimental results were also obtained, verifying the reliability of calculations. These results provide theoretical reference for optimizing the performance of Sb/Bi-doped Mg₂(Si, Sn)-based alloys.