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

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 tomore » 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.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ;  [2] ;  [2] ;  [3] ; ;  [6]
  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. (ThEP), CHE, Ministry of Education, Bangkok 10400 (Thailand)
  4. School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand)
  5. Synchrotron Light Research Institute (Public Organization), 111 University Avenue, Muang District, Nakhon Ratchasima 30000 (Thailand)
  6. Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan)
Publication Date:
OSTI Identifier:
22280723
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 204; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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