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

Figure 1. XRD patterns of the BST+HEA (x = 0, 0.1, 0.5, and 1.0 vol%) for the Pa- and Pe-directions, the ball-milled TaNb HfZrTi high
x
2
entropy alloy (HEA) powder and the calculated data. XRD: X-ray diffraction.
nanoparticles. The enhancements of the σ are primarily attributed to the metallic characteristics of the
TaNb HfZrTi HEA (sintered HEA: σ ~12,500 S cm at 300 K) . Besides, the effect of σ for the HEA
[24]
-1
2
addition is not as pronounced in the Pe-direction of the BST+HEA samples. Since there is no clear trend,
x
the changes in the Pe-direction electrical conductivity of the BST+HEA composite can be attributed to
experimental error.
The temperature-dependent Seebeck coefficients [S(T)] of the hot-pressed BST+HEA (x = 0, 0.1, 0.5, and
x
1.0 vol%) samples for the Pa-direction and Pe-direction are presented in Figure 3B. The S(T) values show
maxima due to the bipolar effect caused by the narrow bandgap (~0.1 eV) of the bismuth tellurides . The S
[40]
-1
values of the pristine BST (224 for the Pa-direction, 216 μV K for the Pe-direction at room temperature)
-1
-1
are comparable with the literature values (235~245 μV K for the Pa-direction, 215~230 μV K for the
Pe-direction at room temperature) . The S of the sintered HEA (TaNb HfZrTi) sample is S = 5.7 μV K at
[11]
-1
2
300 K. The S values of the BST+HEA samples are not significantly affected by the additions of the HEA
x
nanoparticles.
The temperature-dependent power factors [S σ(T)] of the BST+HEA samples for the Pa- and Pe-directions
2
x
2
are presented in Figure 3C. The S σ(T) values of the Pe-direction are higher than those of the Pa-direction
2
due to the higher electrical conductivity resulting from the preferred orientations of the BST layers. The S σ
of the pristine BST (2.7 mW m K for the Pa-direction, 3.6 mW m K for the Pe-direction at room
-1
-2
-1
-2