Investigation of anisotropy in microstructure and thermoelectric properties of large-scaled p-type Bi–Sb–Te sintered body made by hot pressing

In this work, a large-sized pellet of about 200 g (Ф40 × 23 mm) of p-type polycrystalline based Bi–Sb–Te was prepared using gas atomization and hot pressing processes. A systematic investigation was conducted on the microstructural behavior along parallel and perpendicular planes, and the anisotropic behavior of the thermoelectric and mechanical properties was subsequently studied. The X-ray diffraction studies revealed a slight orientation in grains along the perpendicular direction. The electron back scattered diffraction (EBSD) analysis revealed that the grains in both samples were uniformly disseminated throughout the matrix in random directions with an average grain sizes of 4.30, and 4.83 μm, respectively, for the parallel and perpendicular directions. The electrical conductivity and thermal conductivity had higher values along the perpendicular direction compared with the parallel direction, which was attributed to their higher mobility owing to orientation and lower aspect ratio of grain boundaries. The Seebeck coefficient had an isotropic nature. The maximum thermoelectric figure of merit, ZT of 1.2 was achieved at 350 K in the perpendicular specimen, more than 20% higher than the parallel sample. The parallel specimen had a higher compression strength of 105 MPa, and hardness of about 58.75 Hv, due to the microstructural nature of the respective directions. These significantly enhanced large-scale thermoelectric materials can be potentially applicable in power generation and thermoelectric cooling applications, including commercial thermal detector, laser diodes, infrared detectors and sensors.