Research of Donor-like Effect and Thermoelectric Performance in <i>n</i>-Type Bi<sub>2</sub>Te<sub>3</sub>-Based Compounds

Grain size refinement is the vital stratagem for improving mechanical properties of Bi₂Te₃-based compounds. However, the donor-like effect induced by grain size refinement strongly restricts the thermoelectric properties especially in the vicinity of room temperature. Once the donor-like effect is generated, it is very difficult to remove the donor-like effect by the simple heat treatment process and other processes. In this study, the effect of particle size on the donor-like effect and thermoelectric properties was systematically studied for Bi₂Te₃-based compounds. As the particle size decreases, the donor-like effect is enhanced significantly. The oxygen-induced donor-like effect dramatically increases the carrier concentration from 3.36×10¹⁹ cm^-3 for 10 M sintered sample to 7.33×10¹⁹ cm^-3 for 120 M sintered sample, which is largely beyond the optimal carrier concentration of 2.51×10¹⁹ cm^-3 and seriously deteriorates the thermoelectric performance. However, when the particle size of the powder is 1~2 mm, the Seebeck coefficient of -195 μV K^-1 and the carrier concentration of 3.36×10¹⁹ cm^-3 near room temperature are achieved, which are similar to the ZM sample with the Seebeck coefficient of -203 μV K^-1 and the carrier concentration of 2.51×10¹⁹ cm^-3. The powders without the obvious donor-like effect can be used as the excellent raw materials for powder metallurgy process. A maximum ZT value of 0.75 is achieved for the 18 M sintered sample. The excellent thermoelectric properties is expected to obtain by enhancing the texture further. This study provides an important guidance for the preparation of materials with excellent thermoelectric and mechanical properties by powder metallurgy process and provides a new path to regulate and effectively suppress the generation of donor-like effects.