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Synthesis and characterisation of perovskite SrxY1-xFeO3-d (=.63≤x<1) and Sr0.75Y0.25Fe1-yMyO3-d (M=Cr, Mn, Ni) (y= 0.2, 0.33, 0.5)
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). STFC Rutherford Appleton Laboratory, England.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Pierre & Marie Curie University, France.
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2013 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 200, 30-38 p.Article in journal (Refereed) Published
Abstract [en]

Oxygen-deficient ferrates with the cubic perovskite structure SrxY1-xFeO3-d were prepared in air (0.71 ≤ x ≤ 0.91) as well as in N2 (x=0.75 and 0.79) at 1573K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along <100>p with G± ~0.4<100>p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K-1 in air at 298-673K. At 773-1173K TEC increases up to 17.2 ppm K-1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79.

Place, publisher, year, edition, pages
2013. Vol. 200, 30-38 p.
Keyword [en]
Perovskites, neutron diffraction, electron diffraction, high-temperature conductivity, thermal expansion, magnetic susceptibility
National Category
Inorganic Chemistry Materials Chemistry
Research subject
Inorganic Chemistry; Materials Chemistry
URN: urn:nbn:se:su:diva-88792DOI: 10.1016/j.jssc.2013.01.008ISI: 000317158000005OAI: diva2:613567
Studies of cobalt based perovskites for cathode materials in solid oxide fuel cells.
Swedish Research Council, 2007-4348
Available from: 2013-03-28 Created: 2013-03-28 Last updated: 2014-07-29Bibliographically approved
In thesis
1. Properties in New Complex Perovskite-Related Materials, a Matter of Composition and Structure
Open this publication in new window or tab >>Properties in New Complex Perovskite-Related Materials, a Matter of Composition and Structure
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Egenskaper hos nya komplexa perovskitrelaterade material, en fråga om sammansättning och struktur
Abstract [en]

This PhD thesis presents investigations of perovskite-related compounds in systems of interest for applications in components in solid oxide fuel cells. The compound compositions derive from substitutions in the parent compounds LaCoO3, LaCrO3 and SrFeO3.

Novel phases La2Co1+z(MgxTi1-x)1-zO6 were synthesized and investigated with regard to structure, thermal expansion, electronic and magnetic properties. The study focused on the composition lines La2Co(MgxTi1-x)O6 (z=0), where the oxidation state of Co nominally changes from +2 (x=0.0) to +3 (x=0.5), and La2Co1+z(Mg0.5Ti0.5)1-zO6, with a varying fraction of Co3+ ions. XANES data show that the Co ions in the system have discrete oxidation states of +2 and +3. The TEC increases with increasing x due to an increasing contribution from spin state transitions of the Co3+ ions. Novel compounds La2Cr(M2/3Nb1/3)O6 with M=Mg, Ni, Cu were synthesized and characterized with respect to structure and magnetic properties. XRPD and NPD data indicate Pbnm symmetry; however, SAED patterns and HREM images indicate a P21/n symmetry for M=Mg, and Cu. The magnetic measurements results were rationalized using the Goodenough-Kanamori rules.

Oxygen-deficient phases with x≥0.63 in SrxY1-xFeO3-δ and Sr0.75Y0.25Fe1-yMyO3-δ (M=Cr, Mn, Ni and y=0.2, 0.33, 0.5), were synthesized and characterized with respect to structure, oxygen content, thermogravimetry, TEC, conductivity and magnetic properties. Powder patterns of phases agree with cubic  perovskite structures. NPD data for x=0.75 reveal anisotropic displacement for the O atom, related to local effects from Fe3+/Fe4+ ions. SAED patterns for x=0.75 reveal the presence of an incommensurate modulation. The compounds start to lose oxygen in air at ~ 400°C. The TEC up to ~400°C for x=0.75 is ~10.5 ppm/K and increase to ~17.5 ppm/K at higher temperatures. The conductivity for x=0.91 is 164 S/cm at 400°C. Partial substitution of Fe by Cr, Mn or Ni does not increase the conductivity or decrease TEC.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2013. 92 p.
Perovskite, XANES, XRPD, NPD, TEC, TEM, SEM, TGA, SAED, HREM, thermal expansion, Seebeck coefficient, electronic conductivity, SOFC materials, magnetic susceptibility, Perovskit, XANES, XRPD, NPD, TEC, TEM, SEM, TGA, SAED, HREM, termisk expansion, Seebeck koefficient, elektrisk ledningsförmåga, SOFC material, magnetiska egenskaper
National Category
Materials Chemistry
Research subject
Materials Chemistry
urn:nbn:se:su:diva-88793 (URN)978-91-7447-672-9 (ISBN)
Public defence
2013-04-29, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Swedish Research CouncilThe Foundation for Baltic and East European StudiesKnut and Alice Wallenberg Foundation
Available from: 2013-04-08 Created: 2013-03-28 Last updated: 2013-04-02Bibliographically approved

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Biendicho, Jordi JacasShafeie, SamrandGrins, JekabsSvensson, Gunnar
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