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Page 14 of 17 Kumar et al. Energy Mater. 2025, 5, 500109 https://dx.doi.org/10.20517/energymater.2025.22

Figure 7. (A) Temperature-dependent figure of merit ZT of the hot-pressed BST+HEA (x = 0, 0.1, 0.5, and 1.0 vol%) samples for the
x
Pa- and Pe-direction; (B) ZT values as a function of the HEA concentrations at 300 and 350 K; (C) maximum ZT avg. of the BST+HEA x
samples at the T = 425K and T cold = 300 K; (D) average ZT with the literature values [37,41,45-51] . BST: Bi Sb Te ; HEA: high entropy
0.4
hot
3
1.6
alloy.
CONCLUSIONS
In summary, the anisotropic thermoelectric properties of the sintered BST+HEA (x = 0, 0.1, 0.5, and
x
1.0 vol%) samples were investigated. The homogeneously dispersed HEA nanoparticles in the BST matrix
effectively increase the Pa-direction electrical conductivity, without reducing S. The small amounts of the
HEA nanoparticles (below 0.5 vol%) efficiently enhance the mean free path of the carrier for the
Pa-direction of the BST, without significantly altering the carrier concentration. The enhanced electrical
conductivity due to the HEA additions can be attributed to the improved electrical grain connectivity in the
Pa-direction of the BST. The HEA nanoparticles may reduce the electrical potential barriers of the
Pa-direction at grain boundaries. The decrease of κ by scattering of phonons (decrease of λ ) with
L
ph
enhanced electronic mean free path λ for x = 0.1 sample shows the PGEC effect. As a result of the enhanced
e
electrical conductivity and reduced κ with the HEA nanoparticle distribution, a maximum ZT = 1.33 at
L
350 K and high ZT = 1.26 (T = 425K and T = 300 K) were obtained in the 0.1 vol% sample for the
avg.
hot
cold
Pa-direction. The controlling grain connectivity through composites with HEA nanoparticles offers a
promising strategy not only for achieving high ZT values but also for enabling industrial applications