Preparation of Delafossite CuYO 2 by Metal-citric Acid Complex Decomposition Method
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1166-N03-13
Preparation of delafossite CuYO2 by metal-citric acid complex decomposition method. Keishi Nishio1, Tomomi Okada1, Naoto Kikuchi2, Satoshi Mikusu3, Tsutomu Iida1, Kazuyasu Tokiwa3, Tsuneo Watanabe3 and Tohru Kineri4 1
Material Science and Technology, Tokyo University of Science, 2641 Yamzaki, Noda-shi, Chiba 278-8510, Japan 2 Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan 3 Department of Applied Electronics, Tokyo University of Science, 2641 Yamzaki, Noda-shi, Chiba 278-8510, Japan 4 Department of Materials Science & Environmental Engineering, Tokyo University of Science, Yamaguchi, 1-1-1 Daigaku-doori, Sanyo-Onoda-shi, Yamaguchi, 756-0884, Japan
ABSTRACT Delafossite CuYO2 and Ca doped CuYO2 were prepared by thermal decomposition of a metal-citric acid complex. The starting solution consisted of Cu acetate, Y acetate and Ca acetate as the raw materials. Citric acid was used as the chelating agent, and acetic acid and distilled water were mixed as a solvent. The starting solutions were heated at 723 K for 5 h after drying at 353 K. The obtained powders were amorphous and single phase of orthorhombic Cu2Y2O5 was obtained by heat-treated the amorphous powder at a temperature range between 1073 and 1373 K for 3 h in air. Furthermore, Heat-treating the obtained orthorhombic Cu2Y2O5 at above 1373 K in air caused it to decompose into Y2O3, CuO and Cu2O. On the other hand, the sample powder prepared from a starting solution without citric acid, i.e., single phase of orthorhombic Cu2Y2O5 could not be obtained under the same synthesis conditions as that for a solution with citric acid. We were able to obtain delafossite CuYO2 and Ca doped CuYO2 from orthorhombic Cu2Y2O5 under a low O2 pressure atmosphere at above 1223 K. The obtained delafossite CuYO2 composed hexagonal and rhombohedral phases. The color of the CuYO2 powder was light brown and that of Ca-doped CuYO2 was light green. Diffraction peaks in the XRD pattern were slightly shifted by doping Ca for CuYO2, and these peaks shifted toward to a high diffraction angle with an increasing amount of doped Ca. From these results, we concluded that Ca doped delafossite CuYO2 could be obtained by thermal decomposition of a metal-citric acid complex.
INTRODUCTION Thermoelectric materials having the properties of large thermo-power, low resistivity, and low thermo-conductivity have been investigated. Recently, many reseachers have reported ptype semiconductors with layered metal oxides, i.e., Na-Co-O and Ca-Co-O, because they show low resistivity and low thermo-conductivity [1-3]. For example, Ca3Co4O9 consists of Ca2CoO3 and CoO2 blocks alternately stacked along the c-axis to form a layered structure. Thus, the physical properties are highly two-dimensional in an a-b plane compared with those in the c-axis direction. This indicates very high thermoelectric properties. These layered metal oxide compounds promising candidate for thermoelectric application at high
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