Thermoelectric and Mechanical Properties of Ca 0.9 Yb 0.1 MnO 3 Based Materials
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1044-U07-10
Thermoelectric and Mechanical Properties of Ca0.9Yb0.1MnO3 Based Materials Atsuko Kosuga1, Saori Urata2, and Ryoji Funahashi1,2 1 National Institute of Advanced Industrial Science and Technology, 1-8-31, Midorigaoka, Ikeda, Osaka, 563-8577, Japan 2 Japan Science and Technology Agency, 4-1-8, Honmachi, Kawaguchi, Saitama, 332-0012, Japan ABSTRACT The Ca0.9Yb0.1MnO3/Ag composites(the ratio of Ag to Ca0.9Yb0.1MnO3 was 0, 4.7, 9.4, and 18.8 wt %) were prepared by wet milling various amounts of Ca0.9Yb0.1MnO3 and Ag2O powder mixtures followed by sintering in order to improve the mechanical properties of Ca0.9Yb0.1MnO3 for n-type legs of thermoelectric oxide devices. The obtained composites consisted of two phases such as Ca0.9Yb0.1MnO3 and metallic Ag from the X-ray diffraction (XRD) analysis. The scanning electron microscope (SEM) analysis indicated that the Ag particles, the size of which was within 5 µm, were homogeneously dispersed in Ca0.9Yb0.1MnO3 matrix for all the composites. The fracture strength σf of 18.8 wt% Ag composite became 251 MPa, which was 2 times larger value than that of Ca0.9Yb0.1MnO3. The power factor S2ρ−1 didn’t greatly change with Ag addition to Ca0.9Yb0.1MnO3. INTRODUCTION Since the discovery of p-type NaxCoO2 by Terasaki[1], numerous researchers have extensively studied on thermoelectric oxides and p-type CoO2-based oxides with high thermoelectric performance were discovered[2,3]. The n-type counterparts possessing high thermoelectric performance, however, have not been found so far. We focused on the CaMnO3 based material as a good candidate for n-type legs. As a result, a polycrystalline sample of Ca0.9Yb0.1MnO3 was found to exhibit a moderate ZT : 0.16 at 973 K in air[4]. Moreover, thermoelectric devices consisting of CaMnO3 system as n-type legs and Ca3Co4O9 system as ptype legs were fabricated[5]. However, we found that CaMnO3 based materials of n-type legs in the devices broke after the power generation test probably due to the thermal stress, which was attributed to the big difference of the thermal expansion coefficient of the Ag electrode(metal) and CaMnO3 based materials(ceramic), accumulated in the CaMnO3 based materials with inherently low mechanical strength. One possible approach to overcome this problem is to enhance the mechanical properties of CaMnO3 based materials. There are some materials designs to strengthen and toughen ceramics by using composite techniques to incorporate particulate, whisker or platelet reinforcement[6,7]. Among them, ceramic composites having ductile metal dispersion was reported to show excellent mechanical properties such as hardness, Young’s modulus, fracture strength and toughness[8,9]. This paper is presenting an experimental study directed toward the enhancement of the mechanical properties of Ca0.9Yb0.1MnO3 by Ag addition without diluting the electrical properties of Ca0.9Yb0.1MnO3. Ag particle was selected as a dispersion phase because of its high melting point and good electrical conductivity. These properties are good for the com
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