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Phase formation, crystal structures and magnetic properties of perovskite-type phases in the system La2Co1+z(MgxTi1-x)1-zO6
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2011 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, no 1, 177-190 p.Article in journal (Refereed) Published
Abstract [en]

Perovskite-type cobaltates in the system La(2)Co(1+z) (Mg(x)Ti(1-x))(1-z)O(6) were studied for z=0 <= x <= 0.6 and 0 <= x <= 0.9, using X-ray and neutron powder diffraction, electron diffraction (ED), magnetic susceptibility measurements and X-ray absorption near-edge structure (XANES) spectroscopy. The samples were synthesised using the citrate route in air at 1350 degrees C. The space group symmetry of the structure changes from P2(1)/n via Pbnm to R (3) over barc with both increasing Mg content and increasing Co content. The La(2)Co(Mg(x)Ti(1-x))O(6) (z=0) compounds show anti-ferromagnetic couplings of the magnetic moments for the Co below 15 K for x=0, 0.1 and 0.2. XANES spectra show for the compositions 0 <= x <= 0.5 a linear decrease in the L(3)/(L(3)+ L(2))Co-L(2.3) edge branching ratio with x, in agreement with a decrease of the average Co ion spin-state, from a high-spin to a lower-spin-state, with decreasing nominal Co(2+) ion content.

Place, publisher, year, edition, pages
2011. Vol. 184, no 1, 177-190 p.
Keyword [en]
Cobaltates, perovskite, X-ray diffraction, neutron diffraction, magnetic susceptibility, electron diffraction, XANES
National Category
Inorganic Chemistry Physical Chemistry Materials Chemistry
Research subject
Inorganic Chemistry; Materials Chemistry
URN: urn:nbn:se:su:diva-46139DOI: 10.1016/j.jssc.2010.11.002ISI: 000286774600026OAI: diva2:371582
Studier av koboltbaserade perovskiter för användning i bränsleceller
Swedish Research Council, 2007-4348
Available from: 2010-11-26 Created: 2010-11-21 Last updated: 2013-04-02Bibliographically 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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Shafeie, SamrandGrins, JekabsSvensson, Gunnar
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