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Title: Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO{sub 3}

The electronic structure of the (La{sub 0.8}Sr{sub 0.2}){sub 0.98}Mn{sub 1−x}Cr{sub x}O{sub 3} model series (x = 0, 0.05, or 0.1) was measured using soft X-ray synchrotron radiation at room and elevated temperature. O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra showed that low-level chromium substitution of (La,Sr)MnO{sub 3} resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L{sub 3}-edge resonant photoemission spectroscopy measurements indicated lowered Mn 3d–O 2p hybridisation with chromium substitution. Deconvolution of O K-edge NEXAFS spectra took into account the effects of exchange and crystal field splitting and included a novel approach whereby the pre-peak region was described using the nominally filled t{sub 2g}↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t{sub 2g}↑ state, which appears to provide an explanation for the 0.15 eV rise in activation energy for the oxygen reduction reaction, while decreased overlap between hybrid O 2p–Mn 3d states was in qualitative agreement with lowered electronic conductivity. An orbital-level understanding of the thermodynamically predicted solid oxide fuel cell cathode poisoning mechanism involving low-level chromium substitution on the B-site of (La,Sr)MnO{sub 3} is presented.
Authors:
; ;  [1] ; ;  [2] ;  [3] ;  [4]
  1. Laboratory for High Performance Ceramics, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf (Switzerland)
  2. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore (India)
  3. Institute of Physics, Academy of Sciences of the Czech Republic, Prague (Czech Republic)
  4. Materials Science Beamline, Elettra Synchrotron, Trieste (Italy)
Publication Date:
OSTI Identifier:
22489621
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; ABSORPTION SPECTROSCOPY; ACTIVATION ENERGY; CATHODES; CHROMIUM; CRYSTAL FIELD; ELECTRONIC STRUCTURE; EV RANGE; FINE STRUCTURE; MANGANESE OXIDES; OXYGEN; PEAKS; PHOTOELECTRON SPECTROSCOPY; SOFT X RADIATION; SOLID OXIDE FUEL CELLS; SPECTRA; SYNCHROTRON RADIATION; X-RAY SPECTROSCOPY