The formation of nanocrystalline SrFeO 3-δ using mechano-synthesis and subsequent sintering: Structural and Mössbauer studies

H. M. Widatallah, A. D. Al-Rawas, C. Johnson, S. H. Al-Harthi, A. M. Gismelseed, E. A. Moore, S. J. Stewart

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Abstract

The influence of mechanical milling and subsequent sintering of a 2:1 molar mixture of SrCO 3 and Cr-Fe 2O 3 on the formation of SrFeO 3-δ pervoskite-related nanocrystalline particles is investigated. The structural evolution during the formation process is systematically investigated using X-ray diffraction, thermal analysis, X-ray photoelectron spectroscopy and Mössbauer spectroscopy. Premilling the mixture in air for 120 h leads to the incorporation of Sr 2+ in the α-Fe 2O 3 crystal structure thus facilitating the formation of a 2:1 nanocrystalline mixture of SrFeO 3 and SrFeO 2.875 by sintering the pre-milled mixture in air at 800°C (12 h). This temperature is ∼300°C lower than those at which SrFeO 3-δ phases are synthesized by the conventional ceramic techniques. Pre-milling the precursors was found to result in a smaller oxygen deficiency (δ) relative to conventional ceramic synthesis of SrFeO 3-δ. Rietveld refinement of the X-ray diffraction shows the interatomic distances in the resulting SrFeO 2.875 nanocrystalline phase to be slightly different from those of the conventionally prepared bulk leading, in turn, to a crystal structure with tilted polyhedral cationic sites. This structural distortion is related to both small-size and surface effects in the nanoparticles that have no counterparts in the corresponding bulk material. The surface structure of the attained SrFeO 3-δ nanocrystalline particles shows a significant partial reduction of Fe 4+ to Fe 3+ due to ambient conditions and the presence of an appreciable amount of SrCO 3 as well.

Original languageEnglish
Pages (from-to)2510-2517
Number of pages8
JournalJournal of Nanoscience and Nanotechnology
Volume9
Issue number4
DOIs
Publication statusPublished - Apr 2009

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Keywords

  • Ferrates
  • Mechanical milling
  • Mössbauer spectroscopy
  • XPS
  • XRD

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Chemistry(all)
  • Materials Science(all)
  • Bioengineering
  • Biomedical Engineering

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