Na_xCoO_<2-б>単結晶を用いたテンプレート粒成長法及び反応性テンプレート粒成長法により合成した高配向Na_xCoO_<2-б>セラミック

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Textured _<γ->Na_xCoO_<2-σ> ceramics have been prepared by both templated grain growth (TGG) and reactive templated grain growth (RTGG) methods using single-crystalline particles of _<γ->Na_xCoO_<2-σ> as templates. An XRD analysis indicated that the samples were highly c-axis oriented; I.e., the highest Lotgering's factor was estimated to be 0.93. According to transport property measurements, the highly textured _<γ->Na_xCoO_<2-σ> sample exhibited electrical conductivity (σ) =〜1.85×10_4 S/m, Seebeck coefficient (S) =〜137μV/K and power factor (PF=σ・S_2)=0.35 mW・m_-1・K_-2 at 〜 800 K. These values of a and S are smaller than those of single crystals (sc); that is, σ_sc=19.2×10_4S/m and S_sc=200μV/K at 800 K. The magnitude of a was found to decrease in proportion to the relative density (d) of the sample, while S was independent of d. Furthermore, both σ and S seemed to be sensitive to the Na content of the samples. Both the low density (d〜70%) and the deviation from the optimal Na content were considered to be predominant factors for the low thermoelectric properties of the present textured samples.
社団法人日本セラミックス協会の論文
2003-04-01