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Seo et al. Energy Mater. 2025, 5, 500123 Energy Materials
DOI: 10.20517/energymater.2025.38

Article Open Access

Synergistic effect of cation substitution and p-type

anion doping to improve thermoelectric properties in
Zintl phases

1
1
2
1
2
3
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Naeun Seo , Junsu Lee , Yunjeong Lee , Myung-Ho Choi , Ji Hee Pi , Kyu Hyoung Lee , Kang Min Ok , Tae-
Soo You 1,*
1
Department of Chemistry, Chungbuk National University, Chungbuk 28644, Republic of Korea.
2
Department of Chemistry, Sogang University, Seoul 04107, Republic of Korea.
3
Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.
*Correspondence to: Dr. Tae-Soo You, Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644,
Republic of Korea. E-mail: tsyou@chungbuk.ac.kr
How to cite this article: Seo, N.; Lee, J.; Lee, Y.; Choi, M. H.; Pi, J. H.; Lee, K. H.; Ok, K. M.; You, T. S. Synergistic effect of cation
substitution and p-type anion doping to improve thermoelectric properties in Zintl phases. Energy Mater. 2025, 5, 500123.
https://dx.doi.org/10.20517/energymater.2025.38
Received: 16 Feb 2025 First Decision: 6 Apr 2025 Revised: 17 Apr 2025 Accepted: 8 May 2025 Published: 25 Jun 2025
Academic Editors: Yuping Wu, Sung Son Jae Copy Editor: Fangling Lan Production Editor: Fangling Lan

Abstract
Altogether, seven Zintl compounds in the solid solution Ca Yb Zn Cu Sb (0 ≤ x ≤ 1.5, 0 ≤ y ≤ 0.15) system were
9-x x 4.5-y y 9
successfully prepared by the molten Pb-flux and hot-pressing method. From the powder X-ray and single crystal
X-ray diffraction investigations, all these isotypic phases were observed to have been crystallized in the Ca Mn Bi -
9 4 9
type phase (space group Pbam, Z = 2, Pearson code oP45). The overall crystal structure consists of complex
anionic [Zn Sb ] clusters and the space-filling cationic elements. Notably, the central Zn1 site in a triangular
4 9
coordinate exhibited a partial occupation and a relatively large atomic displacement parameter, which was
necessary for the charge balance of the title compounds. All five intra-layer and inter-layer cationic sites showed
the Ca/Yb mixed-occupancy with Yb presenting a specific site-preference for the A3 site. Density functional
theory calculations unveiled a synergistic effect of the Yb-substitution and the p-type Cu-doping increased carrier
concentration by reducing bond polarity through the tuning of the electronegativity difference. Thermoelectric
property measurements further validated that the given synergistic effect was successful in enhancing the
electrical conductivities of the quinary title compounds compared to the parental ternary compound Ca Zn Sb .
9 4.5 9
As a result, the title compound Ca YbZn Cu Sb achieved the largest figure-of-merit of 0.81 at 843 K, which
8 4.4 0.1 9
should be attributed to improved electrical transport properties while maintaining balanced thermal conductivity.
Keywords: Zintl phase, thermoelectric materials, Yb-substitution, p-type Cu-doping

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