Microstructural and Thermoelectric Characteristics of Zinc Oxide-Based Thermoelectric Materials Fabricated Using a Spark Plasma Sintering Process |
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Authors: | Kyoung Hun Kim Seung Hwan Shim Kwang Bo Shim Koichi Niihara Junichi Hojo |
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Affiliation: | Department of Applied Chemistry, Kyushu University, Fukuoka 812-8581, Japan; Department of Ceramic Engineering, Ceramic Processing Research Center, Hanyang University, Seoul 133-791, Korea; Institute for Scientific and Industrial Research, Osaka University, Osaka 567-0047, Japan |
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Abstract: | M-doped zinc oxide (ZnO) (M=Al and/or Ni) thermoelectric materials were fully densified at a temperature lower than 1000°C using a spark plasma sintering technique and their microstructural evolution and thermoelectric characteristics were investigated. The addition of Al2O3 reduced the surface evaporation of pure ZnO and suppressed grain growth by the formation of a secondary phase. The addition of NiO promoted the formation of a solid solution with the ZnO crystal structure and caused severe grain growth. The co-addition of Al2O3 and NiO produced a homogeneous microstructure with a good grain boundary distribution. The microstructural characteristics induced by the co-addition of Al2O3 and NiO have a major role in increasing the electrical conductivity and decreasing the thermal conductivity, resulting from an increase in carrier concentration and the phonon scattering effect, respectively, and therefore improving the thermoelectric properties. The ZnO specimen, which was sintered at 1000°C with the co-addition of Al2O3 and NiO, exhibited a ZT value of 0.6 × 10?3 K?1, electrical conductivity of 1.7 × 10?4Ω?1·m?1, the thermal conductivity of 5.16 W·(m·K)?1, and Seebeck coefficient of ?425.4 μV/K at 900°C. The ZT value obtained respects the 30% increase compared with the previously reported value, 0.4 × 10?3 K?1, in the literature. |
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