Transport Properties of Ca-doped γ-NaxCoO2

Yasuhiro ONO; Nobuhiko KATO; Yuzuru MIYAZAKI; Tsuyoshi KAJITANI

doi:10.14852/jcersjsuppl.112.0.S626.0

Journal of the Ceramic Society of Japan, Supplement 112-1, PacRim5 Special Issue

Session ID : 9

DOI https://doi.org/10.14852/jcersjsuppl.112.0.S626.0

Conference information

Host: The Ceramic Society of Japan

Co-host: Iketani Science and Technology Foundation, International Ceramic Federation, Commemorative Organization for the Japan World Exposition '70, The American Ceramic Society, The Australasian Ceramic Society, The Chinese Ceramic Society, The Korean Ceramic Society, Joint Research Consortium of Synergy Ceramics/Fine Ceramics Research Association, Nanotechnology Researchers Network Center of Japan, The Special Coordination Funds for Promoting Science and Technology, Japan National Tourist Organization, Aichi Prefectural Government, CASIO SCIENCE PROMOTION FOUNDATION, DAIKO FOUNDATION, Nagoya Convention and Visitors Bureau, The Asahi Glass Foundation, The Kao Foundation For Arts And Sciences, The Murata Science Foundation, The Ogasawara Foundation for the Promotion of Science & Engineering, ASAHI GLASS CO., LTD. Research Center, CENTRAL GLASS CO., LTD., ELECTRIC GLASS INDUSTRY ASSOCIATION OF JAPAN (EGAJ), Hattori Company, Ltd., Hitachi Research Laboratory, Hitachi, Ltd., HOYA CORPORATION, INAX Corporation, ITOCHU CERATECH CORP., Japan Cement Association, KYOCERA Corporation, KYUSHU REFRACTORIES CO., LTD., MINO CERAMIC CO., LTD., Murata Manufacturing Co., Ltd., NGK INSULATORS LTD., NGK SPARK PLUG CO., LTD., NICHIAS Corporation, NIKKO COMPANY, Nippon Electric Glass Co., Ltd., Nippon Sheet Glass Co., Ltd., NORITAKE CO., LIMITED, Tokuyama Corporation, TOTO LTD.

Papers

Transport Properties of Ca-doped γ-Na_xCoO₂

Yasuhiro ONO, Nobuhiko KATO, Yuzuru MIYAZAKI, Tsuyoshi KAJITANI

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Keywords: Thermoelectric material, Layered oxide, γ-Na_xCoO₂, Ca-doping

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Abstract

Single-phase polycrystalline samples of γ-Na_0.70Ca_xCoO_2-δ are successfully synthesized in the concentration range, 0≤x≤0.07, by a two-step sintering procedure, i.e., γ-Na_0.70CoO₂ powder mixed with an appropriate amount of Ca(NO₃)₂•4H₂O is sintered at 873 K and 1123 K in air for 12 h. ICP analysis data indicate that Na content (Na/Co=0.64-0.67) is slightly lower than the nominal one (0.70). Oxygen deficiency is determined by the automated iodometric titration technique (δ=0.025-0.033). In this system, formal valence of Co ion linearly decreases from +3.27(2) at x=0 to +3.16(2) at x=0.07, implying electron doping. We have studied thermoelectric properties of γ-Na_0.70Ca_xCoO_2-δ at high temperature. Both electrical resistivity, ρ, and Seebeck coefficient, S, almost linearly increase with increasing temperature. The largest power factor, S²/ρ=6.4×10^-4 W m^-1K^-2 at 985 K, is obtained for the sample with x=0.0175.

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