Redox‐Promoted Tailoring of the High‐Temperature Electrical Performance in Ca3Co4O9 Thermoelectric Materials by Metallic Cobalt Addition
authors Gabriel Constantinescu, Artur R. Sarabando, Shahed Rasekh, Diogo Lopes, Sergii Sergiienko, Parisa Amirkhizi, Jorge R. Frade and Andrei V. Kovalevsky
nationality International
journal Materials 2020, 13(5), 1060
abstract This paper reports a novel composite‐based processing route for improving the electrical performance of Ca3Co4O9 thermoelectric (TE) ceramics. The approach involves the addition of metallic Co, acting as a pore filler on oxidation, and considers two simple sintering schemes. The (1‐ x)Ca3Co4O9/xCo composites (x = 0%, 3%, 6% and 9% vol.) have been prepared through a modified Pechini method, followed by one‐ and two‐stage sintering, to produce low‐density (one‐stage, 1ST) and high‐density (two‐stage, 2ST) ceramic samples. Their high‐temperature TE properties, namely the electrical conductivity (σ), Seebeck coefficient (α) and power factor (PF), were investigated between 475 and 975 K, in air flow, and related to their respective phase composition, morphology and microstructure. For the 1ST case, the porous samples (56%–61% of ρth) reached maximum PF values of around 210 and 140 μWm−1∙K−2 for the 3% and 6% vol. Co‐added samples, respectively, being around two and 1.3 times higher than those of the pure Ca3Co4O9 matrix. Although 2ST sintering resulted in rather dense samples (80% of ρth), the efficiency of the proposed approach, in this case, was limited by the complex phase composition of the corresponding ceramics, impeding the electronic transport and resulting in an electrical performance below that measured for the Ca3Co4O9 matrix (224 μWm−1∙K−2 at 975K).
publisher MDPI Materials
year published 2020
digital object identifier (doi) 10.3390/ma13051060
file materials_13_01060.pdf

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