Grain recovery facilitated low-angle grain boundaries and texture for high-performance BiSbTe alloys

Low-angle grain boundaries (LAGBs) bring an effective scattering of phonons while maintaining a weak effect on charge carrier transport, which could be utilized for enhancing the thermoelectric performance of solid materials. In the Bi₂Te₃-based materials fabricated by hot extrusion (HE) technique, however, the formation of the LAGBs is evitably accompanied by severe recrystallization, resulting in texture loss and hindering further zT improvement. Here, we demonstrate a feasible strategy utilizing the grain recovery to maintain dense LAGBs with high grain orientation by the optimized HE technique. As a result, a low thermal conductivity of about 1 W m⁻¹ K⁻¹ and a high power factor of 4.2 mW m⁻¹ K⁻² are achieved at 300 K for p-type Bi_0.5Sb_1.5Te₃ alloys, leading to a high room-temperature zT of 1.3. Further, with a decent flexural strength of 25.3 MPa, a 23-pair TE cooling module with the dice dimensions of 0.63 × 0.63 × 1.00 mm³ is assembled, which exhibits a maximum temperature difference of 87.8 K at a hot-side temperature T_h of 350 K. These results highlight the important role of grain-recovery manipulation in simultaneously optimizing the thermal and electrical properties toward high-performance Bi₂Te₃-based TE materials.