Journal of the Ceramic Society of Japan, Supplement
Online ISSN : 1349-2756
ISSN-L : 1349-2756
Journal of the Ceramic Society of Japan, Supplement 112-1, PacRim5 Special Issue
Session ID : 9
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Transport Properties of Ca-doped γ-NaxCoO2
Yasuhiro ONONobuhiko KATOYuzuru MIYAZAKITsuyoshi KAJITANI
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Abstract
Single-phase polycrystalline samples of γ-Na0.70CaxCoO2-δ are successfully synthesized in the concentration range, 0≤x≤0.07, by a two-step sintering procedure, i.e., γ-Na0.70CoO2 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-Na0.70CaxCoO2-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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© 2004 The Ceramic Society of Japan
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