Local structure of Fe in Fe-doped misfit-layered calcium cobaltite: An X-ray absorption spectroscopy study

Journal Article · Thu Aug 15 00:00:00 EDT 2013 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2013.05.038· OSTI ID:22280723

Prasoetsopha, Natkrita ^[1]; Pinitsoontorn, Supree ^[2]; Bootchanont, Atipong ^[3]; Kidkhunthod, Pinit ^[4]; Srepusharawoot, Pornjuk; Kamwanna, Teerasak ^[2]; Amornkitbamrung, Vittaya ^[2]; Kurosaki, Ken; Yamanaka, Shinsuke ^[5]

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1. Materials Science and Nanotechnology Program, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand)
2. Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand)
3. School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand)
4. Synchrotron Light Research Institute (Public Organization), 111 University Avenue, Muang District, Nakhon Ratchasima 30000 (Thailand)
5. Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan)

Polycrystalline Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ} ceramics (x=0, 0.01, 0.03, 0.05) were fabricated using a simple thermal hydro-decomposition method and a spark plasma sintering technique. Thermoelectric property measurements showed that increasing Fe concentration resulted in a decrease in electrical resistivity, thermopower and thermal conductivity, leading to an improvement in the dimensionless figure-of-merit, >35% for x=0.05 at 1073 K. An X-ray absorption spectroscopy technique was used to investigate the local structure of Fe ions in the Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ} structure for the first time. By fitting data from the extended X-ray absorption fine structure (EXAFS) spectra and analyzing the X-ray absorption near-edge structure (XANES) spectra incorporated with first principle simulation, it was shown that Fe was substituted for Co in the the Ca{sub 2}CoO{sub 3} (rocksalt, RS) layer rather than in the CoO{sub 2} layer. Variation in the thermoelectric properties as a function of Fe concentration was attributed to charge transfer between the CoO{sub 2} and the RS layers. The origin of the preferential Fe substitution site was investigated considering the ionic radii of Co and Fe and the total energy of the system. - Graphical abstract: The Fe K-edge XANES spectra of: (a) experimental result in comparison to the simulated spectra when Fe atoms were substituted in the RS layer; (b) with magnetic moment; (c) without magnetic moment, and in the CoO{sub 2} layer; (d) with magnetic moment and (e) without magnetic moment. Highlights: • Synthesis, structural studies, and thermoelectric properties of Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ}. • Direct evidence for the local structure of the Fe ions in the Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ} using XAS analysis. • EXAFS and XANES analysis showed that Fe was likely to be situated in the RS layer structure. • Changes in TE property with Fe content was due to charge transfer between the CoO{sub 2} and the RS layers. • Total energy calculation showed energetically favorable Fe substitution in the RS layer.

• OSTI ID: 22280723
• Journal Information: Journal of Solid State Chemistry, Vol. 204; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
ABSORPTION
ABSORPTION SPECTROSCOPY
CALCIUM
CERAMICS
COBALT OXIDES
DECOMPOSITION
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
FINE STRUCTURE
IRON IONS
LAYERS
MAGNETIC MOMENTS
PLASMA
POLYCRYSTALS
SIMULATION
SPECTRA
THERMAL CONDUCTIVITY
THERMOELECTRIC PROPERTIES
TRANSITION ELEMENTS
X RADIATION
X-RAY SPECTROSCOPY