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 Bi0.4Sb1.6Te3 through mechanical alloying to form γ-Al2O3/Bi0.4Sb1.6Te3 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 Bi0.4Sb1.6Te3 samples. The ZT values of the fabricated samples at 298-423 K are 1.0-1.22; these ZT characteristics make γ-Al2O3/Bi0.4Sb1.6Te3 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/Bi0.4Sb1.6Te3 alloy can serve as a high-performance material for application in TE devices.