Toward High-Thermoelectric-Performance Large-Size Nanostructured BiSbTe Alloys via Optimization of Sintering-Temperature Distribution

High thermoelectric performance of mechanically robust p-type Bi₂Te₃-based materials prepared by melt spinning (MS) combined with plasma-activated sintering (PAS) method can be obtained with small, laboratory grown samples. However, large-size samples are required for commercial applications. Here, large-size p-type Bi₂Te₃-based ingots with 30, 40, and 60 mm in diameter are produced by MS-PAS, and the influence of temperature distribution during the sintering process on the composition and thermoelectric properties is systematically studied for the first time. Room-temperature scanning Seebeck Microprobe results show that the large-size ingot is inhomogeneous, induced by ellipsoidal-shape-distributed temperature field during the sintering process, which is verified by finite-element analysis. Although some temperature differences are unavoidable in the sintering process, homogeneity and mechanical properties of ingots can be improved by appropriately extending the sintering time and design of graphite die. Samples cut from ingots attain the peak ZT value of 1.15 at 373 K, about 17% enhancement over commercial zone-melted samples. Moreover, the compressive and bending strengths are improved by several times as well. It is important to ascertain that large-size p-type Bi₂Te₃-based thermoelectric materials with high thermoelectric performance can be fabricated by MS-PAS.