Suppressing the donor-like effect via fast extrusion engineering for high thermoelectric performance of polycrystalline Bi2Te2.79Se0.21

Bi2Te3-based alloys are the most mature commercial thermoelectric (TE) materials for the cooling application near room temperature. However, the poor mechanical properties of the commercial zone melting (ZM) ingot severely limits the further application. Meanwhile, due to the donor-like effect, the robust polycrystalline n-type bulks usually have low TE performance near room temperature. Herein, based on the commercial ZM ingots, a high figure of merit (zT) of 1.0 at 320 K and good mechanical properties are achieved via the hot extrusion. The dynamic recrystallization in the hot-extrusion process can suppress the donor-like effect and refine the large ZM grains into fine-equiaxed grains. Moreover, the obtained polycrystalline Bi2Te2.79Se0.21 has good preferential orientation and high carrier mobility (μ). The high μ and the weaken donor-like effect maintain the high power factor (PF) of 43.1 μW cm−1 K−2 in the hot-extruded ZM sample. Due to the enhanced phonon scattering, the total thermal conductivity κtot decreased to 1.35 W·m−1·K−1. To demonstrate the good mechanical properties of the extruded ZM sample, micro TE dices with the cross sections of 300 μm × 300 μm and 200 μm × 200 μm are successfully cut from the extrusion sample. This study provided a fast and low-cost extrusion technique to improve the TE and mechanical properties of the commercial ZM ingot at room temperature.