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Korean Journal of Metals and Materials > Volume 59(4); 2021 > Article
Korean Journal of Metals and Materials 2021;59(4): 239-246. doi: https://doi.org/10.3365/KJMM.2021.59.4.239
Effects of Charge Compensation on the Thermoelectric Properties of (La1-zCez)0.8Fe4-xCoxSb12 Skutterudites
Kyung-Wook Jang1, Ye-Eun Cha2, Deok-Yeong Choi2, Sunuk Kim3, Won-Seon Seo4, Kyu Hyoung Lee4, Il-Ho Kim2
1Department of Advanced Materials Engineering, Hanseo University, Seosan 31962, Republic of Korea
2Department of Materials Science and Engineering, Korea National University of Transportation, Chungju 27469, Republic of Korea
3Department of Materials Science and Engineering, Adama Science and Technology University, Adama, P.O.Box: 1888, Ethiopia
4Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea
Correspondence  Il-Ho Kim ,Tel: +82-43-841-5387, Email: ihkim@ut.ac.kr
Received: 24 December 2020;  Accepted: 10 February 2021.  Published online: 24 March 2021.
ABSTRACT
La/Ce-partially double-filled and Co-charge-compensated (La1−zCez)0.8Fe4−xCoxSb12 skutterudites were synthesized, and their thermoelectric properties were studied by varying the filling ratio and charge compensation. X-ray diffraction analysis revealed that the matrix phase was skutterudite and a secondary phase was determined to the marcasite FeSb2. However, the formation of marcasite could be inhibited by increasing the Co content. Rare-earth antimonides, including LaSb2 and CeSb2, which were formed in fully filled La1−zCezFe4−xCoxSb12, were not found after La/Ce partial filling. La/Ce filling and Co substitution were confirmed by the decrease in lattice constants, from 0.9137 to 0.9099 nm, with increasing Ce and Co contents. Electrical conductivity showed negative temperature dependence, indicating metallic or degenerate semiconductor characteristics. Intrinsic conduction resulted in the maximum Seebeck coefficient at temperatures between 723 and 823 K. As the Co-substitution and Ce-filling contents increased, the Seebeck coefficient increased, while electrical and thermal conductivities decreased. This was considered to be due to difference in the valences of La3+ and Ce3+/4+ and the increase in carrier concentration caused by Co charge compensation. However, because they had similar atomic masses and ionic radii, the effects of the La/Ce filling ratio were not significant. Instead, Co charge compensation had the dominant effect on thermoelectric properties. The maximum Seebeck coefficient of 165.4 µVK-1 was obtained for (La0.25Ce0.75)0.8Fe3CoSb12 at 823 K, and the highest electrical conductivity of 2.27 × 105 S m-1 was achieved for (La0.75Ce0.25)0.8Fe4Sb12. (La0.25Ce0.75)0.8Fe3CoSb12 exhibited the lowest thermal conductivity of 2.15 W m-1K-1 at 523 K and (La0.75Ce0.25)0.8Fe3.5Co0.5Sb12 showed the highest power factor of 2.53 mW m-1 K-2 at 723 K. The maximum dimensionless figure of merit, ZTmax = 0.71, was achieved at 723 K for (La0.75Ce0.25)0.8Fe3CoSb12.
Keywords: thermoelectric, skutterudite, partial double filling, charge compensation
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