Thermoelectric Performance and Stability of Industrially Zone-Melted P-Type BiSbTe Alloys with High Te Doping

In the preparation process of p-type BiSbTe alloys, conventional powder metallurgy techniques often use excess Te to optimize the performance. Large-scale industrial zone melting also attempts to compensate for Te during raw material preparation. However, it is unclear whether the thermoelectric performance of p-type BiSbTe improves with excess Te in industrial production as well as the thermal stability of the material and devices. This study focuses on p-type zone-melted BiSbTe materials with different doping and solid solution contents. The results show that 3 wt % Te doping increases the maximum ZT from 0.94 to 1.11, with the peak shifting from 393 to 343 K. After annealing at 380 °C, the ZT of the material containing 3 wt % Te decreases to 0.98. After annealing at 250 °C for 1000 h, the ZT value of the sample decreases by 8% overall, with Te secondary phases still present within the bulk. Reliability tests indicate that the ACR change rate of the chemically treated device (p: Bi0.48Sb1.52Te3 + 3 wt % Te, n: Bi2Te2.79Se0.21) is nearly 11%, significantly higher than the 5.07% observed in the chemically untreated device (p: Bi0.48Sb1.52Te3 + 3 wt % Te, n: Bi2Te2.79Se0.21). TEM and EPMA results reveal that elemental Te and Ni formed massive NiTe grains at the barrier layer interface. These grains' growth leads to interfacial voids and cracks, increasing the interfacial contact resistance.