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Kumar et al. Energy Mater. 2025, 5, 500109 Energy Materials
DOI: 10.20517/energymater.2025.22

Article Open Access

Improved thermoelectric performance by grain
connectivity in bismuth antimony telluride

composite with metallic high-entropy alloy
nanoparticles

1,#
1,#
1
2
2
1,#
Anil Kumar , Saurabh Thoravat , Jae Hyun Yun , Rahmatul Hidayati , Junyoung Park , Hyungyu Jin , Jin
1,*
Hee Kim , Jong-Soo Rhyee 1,*
1
Department of Applied Physics and Institute of Natural Sciences, Kyung Hee University, Yongin 17104, Republic of Korea.
2
Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang 37673, Republic of Korea.
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Authors contributed equally.
* Correspondence to: Dr. Jin Hee Kim and Prof. Jong-Soo Rhyee, Department of Applied Physics and Institute of Natural Sciences,
Kyung Hee University, Deogyeong-daero 1732, Yongin 17104, Republic of Korea. E-mail: jinheekim@khu.ac.kr; jsrhyee@khu.ac.kr
How to cite this article: Kumar, A.; Thoravat, S.; Yun, J. H.; Hidayati, R.; Park, J.; Jin, H.; Kim, J. H.; Rhyee, J. S. Improved
thermoelectric performance by grain connectivity in bismuth antimony telluride composite with metallic high-entropy alloy
nanoparticles. Energy Mater. 2025, 5, 500109. https://dx.doi.org/10.20517/energymater.2025.22
Received: 27 Jan 2025 First Decision: 6 Apr 2025 Revised: 16 Apr 2025 Accepted: 23 Apr 2025 Published: 19 May 2025
Academic Editor: Sen Xin Copy Editor: Ping Zhang Production Editor: Ping Zhang

Abstract
We investigated the anisotropic thermoelectric properties of Bi Sb Te (BST) composites with heavy metallic
0.4 1.6 3
high-entropy alloy TaNb HfZrTi (HEA ) (x = 0, 0.1, 0.5, and 1.0 vol%), synthesized by ball-milling, mixing, and
2 x
hot-press sintering method. The HEA additions below 1.0 vol% in the BST+HEA samples do not contribute to the
x
change of Seebeck coefficients, carrier concentrations, and Fermi energies. Besides, electrical conductivity in the
parallel (Pa) direction to the press direction was significantly enhanced due to an increased carrier mean free path
(λ ) from 10.4 nm (x = 0) to 13.6 nm (x = 0.5). This enhanced λ is attributed to metallic HEA nanoparticles that
e e
improve electrical grain connectivity, particularly in the Pa-direction. The lattice thermal conductivities in the
Pa-direction of the BST+HEA samples decreased at x = 0.1 vol% by significant phonon scattering, followed by an
x
increase at higher HEA concentrations (0.5 vol% to 1.0 vol%), which is consistent with the values of the phonon
mean free path. The phonon mean free path and lattice thermal conductivity of the composites indicate the
synergistic competition between the phonon scattering and the grain connectivity in the Pa-direction. As a result,
the thermoelectric figure of merit in the Pa-direction improved from 1.09 (x = 0) to 1.33 (x = 0.1 vol%) at 350 K.
These findings suggest that incorporating heavy metallic HEA nanoparticles is a promising strategy to improve the
performance of the anisotropic thermoelectric materials and other systems sensitive to grain connectivity.

Keywords: Bismuth antimony telluride, high-entropy alloy, grain connectivity, nanoparticles, mean free path,
thermoelectrics

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