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

The p-type (Bi0.25Sb0.75)2Te3 ingot doped with 8 wt% excess Te alone and the n-type Bi2 (Te0.94Se0.06)3 ingot codoped with 0.068 wt% I 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 ρ, Seebeck coefficient α and thermal conductivity κ 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 ρ, α and κ 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, ZT values 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.