Thermoelectric properties and crystal structures in Y doped ＄Ca_{3}Co_{4}O_{9}＄

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We have prepared polysrystalline specimens of Y doped ＄Ca_{3}Co_{4}O_{9}＄ using a conventional solid-state reaction method, and investgated the Y substitution effect on the thermoelectric and magnetic properities. The valence state of Co ions in ＄[(ca_{1-x}Y_x)_{2}CoO_{3}]_{0.62}CoO_{2}(0 leqq x leqq 0.04)＄ has been clarified as ＄Co^{3.2+}＄ in ＄CoO_{2}＄ sheet and ＄Co^{3.6+}＄ in RS-type BL, respectively. In addition,both a broad minimum at around 100K ＄(T_{SDW}^{on})＄ and a broad maximum between ＄T_{SS}^{end}＄ and ＄T_{SS}^{on}＄ in the ρ(T) curve correspond to two magnetic transitions,where ＄T_{SS}^{end}＄ and ＄T_{SS}^{on}＄ could correspond to the spin-state transition of Co ions in the ＄CoO_{2}＄ sheet and in the RS-type BL, respectively. Furthermore,in x= 0.02 and 0.04 samples,the seebeck coeddicient at 800K, show the highest value (S = 176μ V/K) .Therefore, Y doped ＄Ca_{3}Co_{4}O_{9}＄ are potential candidates for the practical use of thermoelectric power generations.
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