Title

Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO3

RIS ID

103339

Publication Details

Tsekouras, G., Boudoire, F., Pal, B., Vondracek, M., Prince, K. C., Sarma, D. D. & Braun, A. (2015). Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO3. Journal of Chemical Physics, 143 (11), 114705-1-114705-7.

Abstract

The electronic structure of the (La0.8Sr0.2)0.98Mn1−xCrxO3 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 nearedge 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 t2g ↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t2g ↑ 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.

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Link to publisher version (DOI)

http://dx.doi.org/10.1063/1.4931033