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Crystal structure and high-temperature properties of the Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta (0 <= x <= 0.75)
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
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Number of Authors: 9
2015 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 227, 45-54 p.Article in journal (Refereed) Published
Abstract [en]

Ruddlesden-Popper n=2 member phases Sr3-xYxFe1.25Ni0.75O7-delta, 0 <= x <= 0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mossbauer spectroscopy. Both samples as-prepared at 1300 degrees C under N-2(g) flow and samples subsequently air-annealed at 900 degrees C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with delta=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mossbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a delta value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mossbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K-1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.

Place, publisher, year, edition, pages
2015. Vol. 227, 45-54 p.
Keyword [en]
Ruddlesden-Popper structure, Oxygen non-stoichiometry, Crystal structure, Mossbauer spectroscopy, Electrical conductivity, Thermal expansion
National Category
Chemical Sciences
URN: urn:nbn:se:su:diva-118924DOI: 10.1016/j.jssc.2015.03.018ISI: 000355639500008OAI: diva2:842633
Available from: 2015-07-21 Created: 2015-07-21 Last updated: 2016-04-26Bibliographically approved

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Grins, JekabsSvensson, Gunnar
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