Preparation and characterization of Ca3(Co,M)4O9+δ type thermoelectric materials using the electrostatic spray deposition method

Abstract

Ca3(Co1-xAlx)4O9+δ, Ca3(Co1-yCuy)4O9+δ, Ca3(Co1-x-yAlxCuy)4O9+δ thin-lms and sintered bodies were prepared by electrostatic spray deposition, a solution-based process. The solid-solution region of Ca3(Co1-x-yAlxCuy)4O9+δ was narrower than the presumed region based on the results for single-element-substituted Ca3(Co1-xAlx)4O9+δ and Ca3(Co1-yCuy)4O9+δ. The electrical conductivity of Ca3(Co0.95Al0.025Cu0.025)4O9 were larger than that of the non-substituted-Ca9Co12O28. The power factor of Ca3(Co0.95Al0.025Cu0.025)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.