Precise Regulation of Carrier Concentration in Thermoelectric BiSbTe Alloys via Magnetic Doping

The Bi₂Te₃-based alloy is the best commercial thermoelectric material around room temperature, although it is extremely difficult to further improve its thermoelectric performance. In this work, we demonstrate that magnetic doping is an effective strategy to regulate the thermoelectric performance of p-type Bi_0.5Sb_1.5Te₃. According to our experiments, it is much more difficult for ferromagnetic Fe/Co to enter the Bi_0.5Sb_1.5Te₃ lattice in comparison with diamagnetic Pb, which can be understood by the "like dissolves like" rule. At the same doping content, Fe and Co provide much lower hole carriers than Pb due to their larger carrier thermal activation energies, indicating that Fe and Co as dopants are very applicable for the fine regulation of the carrier concentration. The Fe/Co-doped samples have higher Seebeck coefficients but less carrier mobilities than the Pb-doped sample since the doped magnetic atoms induce additional carrier scattering. Beyond the solid solubility limit, excess Fe/Co represents as the impurity, which can maintain a high carrier concentration due to the metal-semiconductor contact. Finally, the zT values of ∼1.05 and 1.15 near room temperature have been achieved for the samples with 1.71 at. % Co and 1.80 at. % Fe, respectively.