Preparation and Characterization of Ca₃(Co,M)₄O_9+δ Type Thermoelectric Materials Using the Electrostatic Spray Deposition Method

抄録

Ca₃(Co_1−xAl_x)₄O_9+δ, Ca₃(Co_1−yCu_y)₄O_9+δ, Ca₃(Co_1−x−yAl_xCu_y)₄O_9+δ thin-films and sintered bodies were prepared by electrostatic spray deposition, a solution-based process. The solid-solution region of Ca₃(Co_1−x−yAl_xCu_y)₄O_9+δ was narrower than the presumed region based on the results for single-element-substituted Ca₃(Co_1−xAl_x)₄O_9+δ and Ca₃(Co_1−yCu_y)₄O_9+δ. The electrical conductivity of Ca₃(Co_0.95Al_0.025Cu_0.025)₄O₉ were larger than that of the non-substituted-Ca₉Co₁₂O₂₈. The power factor of Ca₃(Co_0.95Al_0.025Cu_0.025)₄O₉ was approximately the same as that of single phase compounds of Ca₉Co₁₂O₂₈. This phenomenon was presumed to have resulted from the increased hole concentration and mobility of the material. Our evaluations of the thermoelectric performance showed similar trends for the thin-film and the sintered body. However, we observed uneven thickness and porosity in the prepared thin films. These flaws will have to be resolved through adjustments in the process used to prepare the thin films.