Crystal chemistry and redox behaviour of antimony strontium calcium perovskites |
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| Affiliation: | 1. Institut de Ciència de Materials de Barcelona (C.S.I.C.), Campus U.A.B., 08193 Bellaterra, Spain;2. Institut de Ciència de Materials de la Universitat de València, Apartado de correos 22085, 46071, Valencia, Spain;1. Ichikawa Research Center, Sumitomo Metal Mining Co., Ltd., Ichikawa, Chiba, 272-8588, Japan;2. Department of Analytical Technology, Sumitomo Metal Mining Co., Ltd., Ichikawa, Chiba, 272-8588, Japan;3. Department of Product Planning and Development, Sumitomo Metal Mining Co., Ltd., Minato-ku, Tokyo, 105-8716, Japan;1. Cinvestav Unidad Saltillo, Parque Industrial, Ramos Arizpe, Coahuila 25900, Mexico;2. CONACYT-Facultad de Ciencias Químicas, Universidad Autónoma de Coahuila, 25000 Saltillo, Mexico;3. Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Coahuila, 25000 Saltillo, Mexico;4. Materials Science and Engineering Program&Texas Materials Institute, The University of Texas at Austin, TX 78712, USA;1. Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand;2. Department of Chemical and Biomolecular Engineering, University of California Los Angeles, CA 90095, United States;1. Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, E-28049 Madrid, Spain;2. Institut Laue Langevin, BP 156X, Grenoble, F-38042, France;1. Research Center on Advanced Materials and Technologies, Interdisciplinary Research Department – Field Science, Alexandru Ioan Cuza University of Iasi, 11 Carol I Blvd., 700506 Iasi, Romania;2. Dunarea de Jos University of Galati, Faculty of Sciences and Environment, Chemistry, Physics and Environment Department, 111 Domneasca Street, 800008 Galati, Romania;1. Chemistry Division, BARC, Mumbai, 400085, India;2. Homi Bhabha National Institute, Anushakti Nagar, Mumbai, 400094, India;3. UGC-DAE Consortium for Scientific Research, B.A.R.C., Mumbai, 400085, India |
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| Abstract: | The compound Sr2Sb1.4Ca0.6O6 and their reduced forms Sr2Sb1.4Ca0.6O5.17 and Sr2Sb1.4Ca0.6O4.84 have been prepared and characterized by powder X-ray diffraction, electron diffraction, iodometric analyses and thermogravimetric analysis. The three phases with different oxygen stoichiometries are structurally related to the perovskite and show symmetry distortions from the ideal cubic structure (with cell parameter ap). The crystal structure of Sr2Sb1.4Ca0.6O6 may be refined by the Rietveld method from powder X-ray diffraction data using the space group P21/n, and the cell parameters a=5.776(2), b=5.7837(2), c=8.1718(3) Å, β=90.039(3)° with the same structural model than for previously studied Sr2Bi1.4Ca0.6O6. It shows two crystallographically independent B positions with occupancies 100% Sb (site 1) and 40% Sb/60% Ca (site 2) ordered in a 3D NaCl-type arrangement. The reduced phases, Sr2Sb1.4Ca0.6O5.17 and Sr2Sb1.4Ca0.6O4.84, are obtained from Sr2Sb1.4Ca0.6O6 by treatment in Ar or Ar/H2 at 650°C and show respectively the unit cell parameters a≈b≈5.9 Å, c≈8.4 Å (with possible space groups I2/m or Immm), and a=8.4 Å, b=6.0 Å, c=24.2 Å, β=125° (space group C2/c). The reduction process is reversible, and the initial oxidized phase can be obtained from the reduced ones by thermal treatment in oxygen or air, at temperatures close to 500°C. |
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