Enhancing the Thermoelectric Power Factor of Mg₂Si/MgO Composites by Ag and Bi Codoping

A high carrier concentration and mobility reduce the electrical resistivity (ρ) and enhance the power factor (PF) of thermoelectric (TE) materials based on electrical transport optimization. In this study, Ag/Bi codoped (0%, 1%, 2%, and 3% (wt.%)) Mg₂Si/MgO TE material was synthesized by ball milling and hot pressing. The crystal structure, morphology, composition, electrical properties, and TE properties of the Ag/Bi codoped Mg₂Si/MgO samples were analyzed by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, Hall effect measurements, and Seebeck coefficient/electric resistance measurements, respectively. The results confirmed the correlation between the Mg₂Si and MgO structures and indicated that all the samples exhibited n-type thermoelectricity. The Ag/Bi (2 wt.%) co-added Mg₂Si/MgO sample yielded a low ρ of 31 mΩ m, a high Seebeck coefficient (S) of –619 µV K⁻¹, and a high PF of 12.4 µW m⁻¹ K⁻² at room temperature. The PF of this sample is higher than that of the undoped sample by one order of magnitude (1.3 µW m⁻¹ K⁻²). Further, at 773 K, the Ag/Bi (2 wt.%) co-added Mg₂Si/MgO sample exhibited the highest PF of 112 µW m⁻¹ K⁻².