The formation and structure of mechano-synthesized nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 6.4}: XRD Rietveld, Mössabuer and XPS analyses

Journal Article · Fri May 15 00:00:00 EDT 2015 · Materials Research Bulletin

DOI:https://doi.org/10.1016/J.MATERRESBULL.2015.01.026· OSTI ID:22475766

Widatallah, H. M.; Al-Harthi, S. H. ^[1]; Johnson, C. ^[2]; Gismelseed, A. M.; Elzain, M. E.; Yousif, A. A. ^[1]

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1. Department of Physics, Sultan Qaboos University, P.O. Box 36, 123 Al-Khoud, Muscat (Oman)
2. Chemistry Department, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)

Highlights: • The formation of mechano-synthesized nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 7−δ} is investigated. • Pre-milling the reactants substantially lowers the formation temperature. • The core and surface structures were studied. • XRD and {sup 57}Fe Mössbauer spectroscopic analyses indicate the δ-value to be 0.60. • XPS shows a complex surface structure for the mechanosynthesized Sr{sub 3}Fe{sub 2}O{sub 7−δ} nanoparticles. - Abstract: The influence of ball milling and subsequent sintering of a 3:1 molar mixture of SrCO{sub 3} and α-Fe{sub 2}O{sub 3} on the formation of Sr{sub 3}Fe{sub 2}O{sub 7−δ} double perovskite is investigated with different analytical techniques. Milling the mixture for 110 h leads to the formation of SrCO{sub 3}-α-Fe{sub 2}O{sub 3} nanocomposites and the structural deformation of α-Fe{sub 2}O{sub 3} via the incorporation of Sr{sup 2+} ions. Subsequent sintering of the pre-milled reactants’ mixture has led to the partial formation of an SrFeO{sub 3} perovskite-related phase in the temperature range 400–600 °C. This was followed by the progressive development of an Sr{sub 3}Fe{sub 2}O{sub 7−δ} phase that continued to increase with increasing sintering temperature until a single-phased nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 7−δ} phase was attained at 950 °C (12 h). This temperature is ∼350 °C lower than the temperature at which the material is prepared conventionally using the ceramic method. The evolution of different structural phases during the reaction process is discussed. Rietveld refinement of the X-ray diffraction data shows a value of 0.60 for the oxygen deficiency δ, in consistency with the Fe{sup 3+}/Fe{sup 4+} ratio derived from the {sup 57}Fe Mössbauer data recorded at both 300 K and 78 K. The Mössbauer data suggests that the Sr{sub 3}Fe{sub 2}O{sub 6.4} nanoparticles are superparamagnetic with blocking temperatures below 78 K. The surfaces of the Sr{sub 3}Fe{sub 2}O{sub 6.4} nanoparticles were shown to have a complex structure and composition relative to those of their cores with traces of SrCO{sub 3}, SrO and SrFeO{sub 3−δ} being detected.

• OSTI ID: 22475766
• Journal Information: Materials Research Bulletin, Vol. 65; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CRYSTALS
DEFORMATION
FERRITES
IRON 57
MIXTURES
MOESSBAUER EFFECT
NANOCOMPOSITES
NANOPARTICLES
NANOSTRUCTURES
OXYGEN
PEROVSKITE
SINTERING
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
SUPERPARAMAGNETISM
SURFACES
SYNTHESIS
X-RAY DIFFRACTION
X-RAY PHOTOELECTRON SPECTROSCOPY