Thermoelectric Performance of n-Type Polycrystalline Bi₂Te₃ by Melt Spinning Following High-Pressure Sintering

An n-type polycrystalline Bi₂Te₃ bulk sample with nanostructure was successfully fabricated by melt spinning combined with high-pressure sintering (MS + HPS). The hydrothermal method combined with hot pressing (HM + HP), the hydrothermal method combined with high-pressure sintering (HM + HP) and melt spinning combined with hot pressing (MS + HPS) are all used to synthesize Bi₂Te₃ bulk samples. The results show that the bulk sample prepared from MS + HPS has a nanograin microstructure with sizes ranging from 100 nm to 300 nm embedded in the matrix, which is beneficial to improve the thermoelectric performance of the materials. The electrical resistivity of the MS samples is not only lower than the commercial ingots fabricated by zone melting but also lower than other reports on MS. In addition, the thermal conductivity of the MS + HPS sample is equivalent to that of the HM + HP sample from 448 K to 498 K due to higher pressure and the nanograins embedded in the matrix. As a result, the ZT values of the MS + HPS sample are higher than that of the other samples and the maximum ZT value of MS + HPS sample reaches 0.74 at 498 K, which is comparable to the maximum value of commercially prepared zone-melted Bi₂Te₃ ingots. Melt spinning combined with high-pressure sintering proved to be an effective alternative way to improve thermoelectric performance of thermoelectric nanocrystalline bulk materials.