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Synthesis and characterisation of the novel double perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu
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).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2012 (English)In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 47, no 9, 2449-2454 p.Article in journal (Refereed) Published
Abstract [en]

The novel perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, and Cu have been synthesised at 1350 degrees C in air via the citrate route. Rietveld refinements using neutron powder diffraction (NPD) data showed that the compounds adopt the GdFeO3 type structure with space group Pbnm, and unit cell parameters a approximate to b approximate to root 2 x a(p) and c approximate to 2 x a(p), where a(p) approximate to 3.8 angstrom. Selected area electron diffraction (SAED) of B = Ni and Cu samples confirmed space group Pbnm. However, distinct reflections forbidden in Pbnm symmetry, but allowed in the monoclinic sub-group P2(1)/n and unit cell parameters a approximate to b approximate to root 2 x a(p) and c approximate to 2 x a(p), beta approximate to 90 degrees were present in SAED patterns of B = Mg sample. This indicates an ordering of the B-cations within the crystal structure of La2CrMg2/3Nb1/3O6. High-resolution electron microscopy (HREM) study indicating uniform, without formation of clusters, ordering of B-cations in the crystallites of La2CrMg2/3Nb1/3O6. Magnetic susceptibility measurements show that the compounds are antiferromagnetic (with some glass or spin clustering effects due to additional ferromagnetic interactions between the B-cations) with T-N for La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu being 90, 125 and 140K, respectively.

Place, publisher, year, edition, pages
2012. Vol. 47, no 9, 2449-2454 p.
Keyword [en]
Inorganic compounds, Oxides, X-ray diffraction, Neutron scattering, Crystal structure, Magnetic properties
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-81827DOI: 10.1016/j.materresbull.2012.05.019ISI: 000309081400052OAI: oai:DiVA.org:su-81827DiVA: diva2:565439
Note

AuthorCount:11;

Available from: 2012-11-07 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically 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.
Keyword
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
Identifiers
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)
Opponent
Supervisors
Funder
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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