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Kumar et al. Energy Mater. 2025, 5, 500109 https://dx.doi.org/10.20517/energymater.2025.22 Page 7 of 17

Figure 3. (A) Temperature-dependent electrical conductivities σ(T); (B) Seebeck coefficients S(T); (C) temperature-dependent power
2
factors S σ(T) of the BST+HEA (x = 0, 0.1, 0.5, and 1.0 vol%) samples for the Pa- and Pe-directions; (D) room-temperature electrical
x
conductivities and Seebeck coefficients as a function of the HEA concentrations (error bar: 5%). BST: Bi Sb Te .; HEA: high entropy
3
1.6
0.4
alloy.
Figure 4A shows that the n of the hot-pressed BST+HEA (x = 0, 0.1, 0.5, and 1.0 vol%) samples are slightly
H
x
enhanced at the 0.1 vol% sample, but are not significantly affected in the range from 0.5 vol% to 1.0 vol%.
The trends in the n values of the BST with the HEA additions are notably different compared to those with
H
[37]
[41]
other doping elements such as Ni, Sn , Pb, Fe, Co and Ag , as shown in Figure 4B. The less susceptible
[10]
n values of the BST+HEA samples suggest that the HEA nanoparticles exist in the BST matrix without
H
x
significant chemical reactions that would alter the carrier concentrations. This behavior is attributed to the
structural stability of the HEA nanoparticles . The stable structural phase of the HEA nanoparticles may
[20]
promote the formation of an ideal composite with BST, without inducing chemical doping effects. Further
detailed investigations are required to understand the unchanged carrier concentrations in the BST+HEA
composite.
Using σ = neμ, where n, e, and μ are the carrier concentration, elementary charge, and carrier mobility,
respectively , the Hall mobilities (μ ) of the BST+HEA samples were investigated. Figure 4C shows that
[2,5]
H
x
the enhancements in the μ are observed in the Pa-direction at low HEA concentrations, in contrast to the
H
less susceptible μ of the Pe-direction. Although the μ is enhanced to the Pa-direction, the μ values of the
H
H
H
BST with the HEA additions are not significantly changed compared to those with other doping elements
[10]
[37]
such as Ni, Sn , Pb, Fe, Co and Ag , as shown Figure 4D.
[41]