Effect of high pressure torsion on crystal orientation to improve the thermoelectric property of a Bi_2Te_3-based thermoelectric semiconductor

摘要

A Bi_2Te_3-based thermoelectric semiconductor was subjected by high pressure torsion (HPT). Sample disks of p-type Bi_(0.5)Sb_(1.5)Te_(3.0) were cut from sintered compacts that were made by mechanically alloying (MA) followed by hot pressing. Disks were subjected by HPT with 1, 5 and 10 turns at 473 K under 6.0 GPa of pressure. Crystal orientation was investigated by X-ray diffraction. Microstructures were characterized using scanning electron microscopy. Results indicated that HPT disks after 5 turns had a preferred orientation and a fine grain compared with pre-HPT disks while the orientation factor was decreased after HPT using 10 turns. The power factor had a maximum value at 5 turns as determined by measuring its thermoelectric properties. A maximum power factor of 4.30×10~(-3) Wm~(-1)K~(-2) was obtained for HPT disks after 5 turns. This value was larger than that for the pre-HPT disk. The over-HPT of 10 turns was found to have caused a decrease in the preferred orientation leading to a low power factor.