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

The p-type (Bi0.25Sb0.75)(2)Te-3 ingot doped with 8 wt% excess Te alone and the n-type Bi-2 (Te(0.94)Sec(0.06))(3) ingot codoped with 0.068 wt% 1 and 0.017 wt% Te were grown by the Bridgman method and annealed at 673 K for 5 h in a hydrogen stream. The electrical resistivity p, Seebeck coefficient alpha and thermal conductivity K before and after annealing were measured at 298 K, so that the annealing degraded significantly ZT of the p-type specimen but enhanced remarkably that of the n-type one. The temperature dependences of p, alpha and K of the as-grown p-type and annealed n-type specimens with higher ZT were investigated in the temperature range from 200 to 360 K. As a result, ZTvalues of the as-grown p-type and annealed n-type specimens have a broad peak and reached great values of 1.19 and 1.13 at approximately 320 K, respectively. The present materials were thus found to be far superior to any other bismuth-telluride compound in the thermal stability of energy conversion efficiency in addition to the high performance. (c) 2005 Springer Science + Business Media, Inc.