Degraded thermal stability of p-type Bi_2Te_3-based polycrystalline bulks for thermoelectric power generation at service temperature of 473K

摘要

The Bi_2Te_3-based bulks are promising thermoelectric materials in the low temperature waste heat recovery area. However, their thermal stability needs to be addressed before they are applied in practical thermoelectric devices. In this work, the long-term thermal stabilities of the micro-structure, thermoelectric properties and mechanical properties for the p-type Bi_(0.44)Sb_(1.56)Te_3 polycrystalline bulks have been investigated at 423 and 473 K. The results indicated that the samples could keep the satisfying thermal stability when the service temperature was fixed at 423 K, and the grain size, the volume, the density and the thermoelectric properties of the samples remained almost unchanged during long term service, and the electrical transport properties were even improved with prolonging the servicing time to 168 h. However, when the service temperature was fixed at 473 K, the volume expansion was obvious with prolonging service time, and great quantity of voids were appeared in the bulks due to Te volatilization, which resulted in the obvious increase of the electrical resistivity and the deterioration of the electrical transport properties, and the unsatisfactory decrease of the power factor and the figure of merit. These results suggest that the long-term service temperature of p-type Bi_2Te_3-based polycrystalline bulks is only 423 K for the low-temperature thermoelectric power generation.