abstract
This work explores the possibilities for a further enhancement of the thermoelectric properties of Ca3Co4O9 by Sr-doping combined with hot-pressing. Modified hot-pressing process resulted in highly-textured and dense ceramics. Sr-doping significantly improves electrical properties, resulting in extremely large power factor (1.2 mW/K-2 m at 800 degrees C) due to simultaneous electrical resistivity decrease and Seebeck coefficient increase. The main effect on cumulative electrical performance is provided by the Seebeck coefficient, reaching 270 mu V/K at 800 degrees C. XPS revealed relatively high average cobalt oxidation state at room temperature (+ 3.3), compared to materials produced by conventional sintering. The results of combined XPS and Auger electron spectroscopy emphasize the importance of high densification in Ca3Co4O9-based ceramics for preventing phase decomposition and interaction with CO2 and moisture. Still, despite the exceptional electrical performance, the calculated figure-of-merit (estimated as 0.29 at 800 degrees C) is around the best reported in the literature due to a high thermal conductivity (4.4 W/K m at room temperature).
keywords
MAGNETIC-PROPERTIES; LAYERED COBALTITES; PHASE-EQUILIBRIA; GROUP-II; CERAMICS; OXIDE; TRANSPORT; CA; MICROSTRUCTURE; FABRICATION
subject category
Materials Science
authors
Torres, MA; Costa, FM; Flahaut, D; Touati, K; Rasekh, S; Ferreira, NM; Allouche, J; Depriester, M; Madre, MA; Kovalevsky, AV; Diez, JC; Sotelo, A
our authors
Andrei Kavaleuski
Principal Researcher
Nuno Miguel Freitas Ferreira
Post-Doc Fellowship
Shahed Rasekh
Junior Researcheracknowledgements
M. A. Torres, M. A. Madre, J. C. Diez, and A. Sotelo thank the Spanish MINECO-FEDER (MAT2017-82183-C3-1-R) and Gobierno de Aragon-FEDER (Research group T54-17R), for financial support. Authors acknowledge the use of Servicio General de Apoyo a la Investigacion-SAI, Universidad de Zaragoza. N.M. Ferreira, A.V. Kovalevsky and F.M. Costa acknowledge the i3N (UID/CTM/50025/2013), CICECO-Aveiro Institute of Materials (UID/CTM/50011/2013) and POCI-01-0145-FEDER-031875 project financed by COMPETE 2020 Program, FCT/MEC and FEDER, POCI in its FEDER/FNR component, under the PT2020 Partnership Agreement. The support from FCT (Portugal) grants SFRH/BPD/111460/2015 and IF/00302/2012, are also acknowledged. Sh. Rasekh acknowledges a FCT grant (SFRH/BPD/124238/2016).