title: Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO3.
abstract: The electronic structure of the (La(0.8)Sr(0.2))(0.98)Mn(1-x)Cr(x)O3 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)MnO3 resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L3-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(2g) ↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t(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)MnO3 is presented.
authors.affiliation: Laboratory for High Performance Ceramics, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
authors.forename: George
authors.initials: G
authors.lastname: Tsekouras
authors.affiliation: Laboratory for High Performance Ceramics, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
authors.forename: Florent
authors.initials: F
authors.lastname: Boudoire
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
authors.forename: Banabir
authors.initials: B
authors.lastname: Pal
authors.affiliation: Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Vondráček
authors.affiliation: Materials Science Beamline, Elettra Synchrotron, Trieste, Italy.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Prince
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
authors.forename: D D
authors.initials: DD
authors.lastname: Sarma
authors.affiliation: Laboratory for High Performance Ceramics, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
authors.forename: Artur
authors.initials: A
authors.lastname: Braun