High performance n-type bismuth telluride with highly stable thermoelectric figure of merit

The n-type Bi2(Te0.94Se0.06)3 ingots doped with and without 0.010 wt. % CuBr in addition to the codoping of 0.102 wt. % I and 0.026 wt. % Te were grown by the Bridgman method at a rate of 6 cm/h. The thermoelectric properties of these specimens were measured before and after annealing, where annealing was done in the temperature range from 473 up to 673 K for 2–5 h in a vacuum and a hydrogen stream. When the n-type specimens doped without and with CuBr were annealed for 2 h at 473 K in a hydrogen stream and at 573 K in a vacuum, respectively, the thermoelectric figure of merits ZT at 298 K for CuBr nondoped and doped specimens were enhanced by 37% and 20% and reached great values of 1.04 and 0.91, respectively. The thermal stability of the ZT of the former specimen was improved significantly by optimizing the total additional content of I and Te alone, so that the ZT changed little with temperature, at least in the temperature range from 298 to 433 K. In addition, this specimen also exhibited a remarkably high power factor of 6.57×10−3 W/mK2 at 298 K, which is the greatest among the bismuth tellurides reported previously.