Thermoelectric properties of alumina-doped Bi_0.4Sb_1.6Te₃ nanocomposites prepared through mechanical alloying and vacuum hot pressing

In this study, γ-Al₂O₃ particles were dispersed in p-type Bi_0.4Sb_1.6Te₃ through mechanical alloying to form γ-Al₂O₃/Bi_0.4Sb_1.6Te₃ composite powders. The composite powders were consolidated using vacuum hot pressing to produce nano- and microstructured composites. Thermoelectric (TE) measurements indicated that adding an optimal amount of γ-Al₂O₃ nanoparticles improves the TE performance of the fabricated composites. High TE performances with figure of merit (ZT) values as high as 1.22 and 1.21 were achieved at 373 and 398 K for samples containing 1 and 3 wt % γ-Al₂O₃ nanoparticles, respectively. These ZT values are higher than those of monolithic Bi_0.4Sb_1.6Te₃ samples. The ZT values of the fabricated samples at 298-423 K are 1.0-1.22; these ZT characteristics make γ-Al₂O₃/Bi_0.4Sb_1.6Te₃ composites suitable for power generation applications because no other material with a similarly high ZT value has been reported at this temperature range. The achieved high ZT value may be attributable to the unique nano- and microstructures in which γ-Al₂O₃ nanoparticles are dispersed among the grain boundary or in the matrix grain, as revealed by high-resolution transmission electron microscopy. The dispersed γ-Al₂O₃ nanoparticles thus increase phonon scattering sites and reduce thermal conductivity. The results indicated that the nano- and microstructured γ-Al₂O₃/Bi_0.4Sb_1.6Te₃ alloy can serve as a high-performance material for application in TE devices.