Grain Size‐Dependent Thermoelectric Performances of Al2O3 Addition into BiSbTe Alloy During Heat Treatment Fabricated by Mechanical Alloying

Herein, the effect of grain size and its texture orientations on the microstructural and thermoelectric performances of Al 2 O 3 nanofiber (6 wt%)‐doped p‐type BiSbTe (BST)/Al 2 O 3 (N) composite before and after heat treatment is revealed. The results are also compared with the spherical Al 2 O 3 particle addition of BST/Al 2 O 3 (S) composite. BiSbTe powders are fabricated through water atomization and BST/Al 2 O 3 composites using ball milling followed by spark plasma sintering to obtain bulk compaction. The grain sizes are in the submicrometer ranges for BST/Al 2 O 3 composites; however, it is found to increase after heat treatment, implying that an increment of electrical conductivity for the heat‐treated BST/Al 2 O 3 (N) leads to the enhancement in the power factor of 2.1 mW m −1 K − 2 at 375 K. On the other hand, the lattice thermal conductivity ( κ ph ) is significantly reduced to 0.52 W m −1 K −1 at 400 K and the corresponding thermal conductivity ( κ ) of 0.89 W m −1 K −1 is attributed to the effective phonon scattering via an interface between low‐dimensional nanofiber of Al 2 O 3 and BST bulk. Also, highly textured grain orientations after heat treatment help to enhance phonon scattering despite larger grain size. Overall, a substantial enhancement of the figure of merit ZT max. 0.95 at 400 K is compared to BST/Al 2 O 3 (S)_HT (=0.7).