Bismuth telluride compounds with high thermoelectric figures of merit

The thermoelectric properties of the p-type (Bi0.25Sb0.75)2Te3 doped with 8 wt. % excess Te and the n-type Bi2(Te0.94Se0.06)3 doped substantially with 0.07 wt. % I, 0.02 wt. % Te, and 0.03 wt. % CuBr which were grown by the Bridgman method at a rate of 6 cm/h 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. No annealing effect on the power factor was observed for the p-type specimen, but the as-grown p-type specimen exhibited a large power factor of 5.53×10−3 W/mK2 at 308 K and a low thermal conductivity of 1.21 W/mK. When the n-type specimen was annealed at 473 K for 2 h in a hydrogen stream, however, the power factor at 308 K increased significantly from 3.26×10−3 to 4.73×10−3 K−1 but its thermal conductivity then increased by about 3% from 1.26 to 1.30 W/mK. As a result, the maximum thermoelectric figure of merits Z at 308 K for the as-grown p- and annealed n-type specimens reached surprisingly great values of 4.57×10−3 K−1 and 3.67×10−3 K−1, respectively, with corresponding ZT values of 1.41 and 1.13. The present materials are sure to belong to the highest class in the Z and ZT values as bismuth telluride bulk compounds.