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1 Department of Energy Conversion and Storage, Technical University of Denmark 2 Electrofunctional materials, Department of Energy Conversion and Storage, Technical University of Denmark 3 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
A rapid method for the synthesis of Ca3Co4O9+δpowder is introduced. The procedure is a modification of the conventional citric-nitrate sol–gelmethod where an auto-combustion process is initiated by a controlled thermal oxidation–reduction reaction. The resulting powders inherit theadvantages of a wet chemical synthesis, such as morphological and compositional homogeneity, and fine, well-defined particle sizes comingfrom the controlled nature of the auto-combustion. Optimized spark plasma sintering (SPS) processing conditions were determined and used tofabricate dense and highly c-axis oriented samples. The microstructure and thermoelectric transport properties were determined both parallel (||)and perpendicular (⊥) to the SPS pressure axis in order to investigate any possible anisotropy variations in the transport properties. At 800°C,power factors of 506 μW/m K2(⊥) and 147 μW/m K2(||), thermal conductivities values of 2.53 W/m K (⊥) and 1.25 W/m K (||), and resulting figures-of-merit, ZT, of 0.21 (⊥) and 0.13 (||) were observed.© 2013 Elsevier Ltd. All rights reserved.
European Ceramic Society. Journal, 2014, Vol 34, Issue 4, p. 925-931
Thermoelectric; Ca3Co4O9; Auto-combustion; Sol–gel; Citrate–nitrate; Spark plasma sintering
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