Complex microstructure induced high thermoelectric performances of p-type Bi–Sb–Te alloys

In this research, we have fabricated the complex microstructure features along with the high density of twin boundaries using the combination of magnetic pulse compaction (MPC) and spark plasma sintering (SPS), which are exclusively improved the thermoelectric transport properties of p-type Bi0.5Sb1.5Te3 alloys via effective scattering of carriers and phonons at the grain boundary interfaces. The texture analysis confirmed the formation of bimodal (mixed grains) microstructural features in MPC + SPS specimens sintered at 350 °C, and 400 °C respectively due to the adhesion of fine grains (grain growth) and initiation of recrystallization at high temperatures. In addition to high density of twin structure, high-angle grain boundaries have also been identified. The power factor of 3.53 mW/m.K2 was obtained for the MPC + SPS at 400 °C due to increased Seebeck coefficient and larger electrical conductivity values. The maximum reduced thermal conductivity of 1.14W/mK was recorded due to a significant reduction in lattice thermal conductivity, which is mainly owing to strong scattering of phonons at the formation of mixed grain microstructures with high-density dislocations. As a result, maximum figure of merit, ZT = 1.17was achieved for MPC + SPS at 400 °C temperature.