Fluctuation of surface composition and chemical states at the hetero-interface in composites comprised of a phase with perovskite structure and a phase related to the Ruddlesden-Popper family of compounds

Elena Yu Konysheva, Michail V. Kuznetsov

Research output: Journal PublicationArticlepeer-review

17 Citations (Scopus)

Abstract

Surfaces and interfaces in composite solids can possess particular compositions and properties, thereby governing the functions of materials. X-ray photoelectron spectroscopy (XPS) has been used for the first time to explore the cation rearrangement between the surface and bulk material of the crystallites in the two-phase composites formed in the La-Sr-Pr-Co-O system. The two-phase composites contain a perovskite phase (major fraction) and a layered perovskite-like phase (La,Sr,Pr)2CoO4±δ related to the Ruddlesden-Popper family of compounds. The difference between the surface and nominal composition was revealed for all the composites explored. The surface concentrations of Pr and La cations are lower compared to the nominal stoichiometry, suggesting their preferable dissolution into the volume of the crystallites. Both Pr3+ and Pr4+ cations coexist at the surface. The surface of all the composites is enriched in Sr cations that could exist as SrCO3, SrO2, and Sr(OH)2 individual surface phases as well as SrO on the surface of the perovskite phase. The second phase plays an important role in balancing the surface composition at the hetero-interface in the composites. The rise in the fraction of (La,Sr,Pr)2CoO4±δ in the composites changes the "surface Sr:bulk Sr" ratio, increasing the later contribution due to the stronger accommodation of Sr cations within its crystal lattice and decreasing the surface depletion of Co cations. In addition to Co3+ and Co4+ cations, a small fraction of Co2+ cations exists in the near-surface region of the composites. The surface of all the composites is strongly enriched in oxygen (by 11.8-13.3 at %). The O1s spectra of the composites contain contributions from the lattice oxygen related to the perovskite phase and layered (La,Sr,Pr)2CoO 4±δ phase as well as different surface oxygen states. The effect of surface treatment on the evolution of the surface composition has been discussed.

Original languageEnglish
Pages (from-to)14114-14122
Number of pages9
JournalRSC Advances
Volume3
Issue number33
DOIs
Publication statusPublished - 7 Sep 2013
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry (all)
  • Chemical Engineering (all)

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