ICT2014 Abstracts

Thermoelectric(TE) materials, which can directly convert heat energy to electrical energy through the Seebeck effect, are expected to help save energy by utilizing waste heat. The oxide thermoelectric material Ca₃Co₄O₉ has attracted attention as an important candidate for high temperature p-type thermoelectric materials because it has good thermal and chemical stability in air at high temperature. The practical application of this material, however, has been limited by low conversion efficiencies of bulk Ca₃Co₄O₉. The thermoelectric performance is evaluated by the dimensionless figure of merit (ZT=S2σ/κ) where S, σ and κ are the Seebeck coefficient, electrical conductivity and thermal conductivity. High S, high σ and low κ are required to improve the energy conversion efficiency. Many different approaches were used to enhance the efficiencies of Ca₃Co₄O₉, which included microstructure and interface engineering. The effect of partial substitution for Ca in Ca₃Co₄O₉ on the thermoelectric properties has been studied, which was successfully used to improve the efficiencies. The effect of Ag addition, which has been known to improve the electrical connection between Ca₃Co₄O₉ grains, has been reported. In this study, the combined effect of Ag addition and the substitution of Sr and Bi for Ca on the thermoelectric properties of Ca₃Co₄O₉ was investigated. Metallic Ag powder was added to the Ca₃Co₄O₉ with either Sr or Bi substitution, and the mixture was ground and spark plasma sintered to fabricate bulk thermoelectric materials. Optimized sintering conditions were used to control the size/distribution of Ag particles. XRD analyses were used to identify the phases of the sintered samples, and the microstructure of each sample was observed by FE-SEM. The Seebeck coefficients and electrical conductivities were measured and used to study the effect of Ag addition and partial substitution on the thermoelectric performance of Ca₃Co₄O₉.