Electronic Transport Properties of Bi₂Te_2.7Se_0.3 Fabricated by Hot Extrusion

Herein we report the optimized processing conditions of hot extrusion for fabricating an n-type Bi₂Te_2.7Se_0.3 thermoelectric compound, with high electronic transport properties as well as improved mechanical reliability. We fabricated a Bi₂Te_2.7Se_0.3 extrudate that was 3.8 mm in diameter and 700 mm in length by controlling the processing parameters of temperature and pressure. A 3-point bending strength of over 70 MPa, which is 7 times higher that of the commercial zone melting ingot, was obtained in the samples prepared at 460 ^oC temperature under 6–6.5 MPa pressure. The samples benefitted from the formation of a highly-dense microstructure (relative density > 98%). It is noted that the electronic transport properties (electrical conductivity and Seebeck coefficient) could be manipulated by controlling the applied pressure of hot extrusion at 460 ^oC, mainly due to the change in the characteristics of the 00l crystal orientation, which originated from grain rotation and rearrangement. Power factor values of ~2.9 mW/mK² at 300 K and ~2.95 mW/mK² at 320 K, similar to those of sintered bulks, were obtained in the hot extrudate fabricated under processing parameters of 460 ^oC and 6 MPa. Moreover, a high power factor value of 2.25 mW/mK² was observed even at the high temperature of 480 K, which is 70% higher than that of Bi₂Te_2.7Se_0.3 bulk fabricated by hot pressing.