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

Journal Article · Mon Sep 21 00:00:00 EDT 2015 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4931033· OSTI ID:22489621

Tsekouras, George; Boudoire, Florent; Braun, Artur ^[1]; Pal, Banabir; Sarma, D. D. ^[2]; Vondráček, Martin ^[3]; Prince, Kevin C. ^[4]

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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)

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.

• OSTI ID: 22489621
• Journal Information: Journal of Chemical Physics, Vol. 143, Issue 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

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