Shear extrusion method of Bi-Te based thermoelectric material

For improvement of the figure of merit in Bi-Te system, anisotropic microstructure control becomes very important with grain size refinement. The conventional powder compaction processes are mostly ineffective or inefficient in texture control. New alternative processing is strongly awaited to make anisotropic microstructure control for enhancement of thermoelectric properties. In this study, the shear extrusion processing was proposed to make texture control in Bi_0.4Sb_1.6Te₃ alloyment from green compact. In this method, strong shear strain is applied to the sample, resulting in selective shear deformation along the cleavage crystal surface and rearrangement of crystalline orientations through the extrusion passage. As the result, the electrical resistivity of sheared sample was improved from 2.11×10^-5 (Ωm) to 1.17×10^-5 (Ωm) without decrease of Seebeck coefficient. Then, higher power factor of 4.09×10^-3 (W/mK²) can be achieved.