Synthesis and characterization of R{sub 2}MnTiO{sub 7} (R = Y and Er) pyrochlores oxides

Journal Article · Sun Sep 01 00:00:00 EDT 2013 · Materials Research Bulletin

DOI:https://doi.org/10.1016/J.MATERRESBULL.2013.05.003· OSTI ID:22341773

Alonso, J. A. ^[1]; Fernández, M. T. ^[2]

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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)

Graphical abstract: - Abstract: New pyrochlore-like phases of composition R{sub 2}MnTiO{sub 7} (R = Er and Y) have been synthesized by a soft-chemistry procedure involving citrates of the different metal ions followed by thermal treatments at moderate temperatures (850 °C for 12 h in air). A characterization by X-ray diffraction and neutron powder diffraction (NPD) has been carried out in order to determine the crystal structure features: these phyrochlores are cubic, space group Fd-3m, defining an intrinsically frustrated three-dimensional system. The Rietveld-refinement from NPD data at room temperature evidences an antisite cation disorder (distribution of Mn between A and B positions) that is accompanied by an increment of the oxygen-vacancy concentration due to the reduction of Mn{sup 4+} at the B position to Mn{sup 2+} at the A position. Thermogravimetric analysis (TGA) was useful to evaluate the stability of these oxides in reducing conditions up to 500 °C. Magnetic susceptibility measurements indicate a ferromagnetic behavior, due to the random distribution of Mn{sup 4+} ions in the octahedral sublattice. At lower temperatures there is a polarization of the R{sup +3} magnetic moments, which also participate in the magnetic structure. Aiming to evaluate these materials as possible electrodes for solid oxide fuel cells (SOFC) we determined that the thermal expansion coefficients between 100 and 900 °C perfectly match with those of the usual electrolytes; however, these pyrochlore oxides display a semiconductor-like behavior with poor conductivity values, e.g. 6 × 10{sup −3} cm{sup −1} at 850 °C for Er, which would prevent its use as MIEC (mixed ionic-electronic conductors) oxides in SOFC devices.

• OSTI ID: 22341773
• Journal Information: Materials Research Bulletin, Vol. 48, Issue 9; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CATIONS
ELECTROLYTES
HEAT TREATMENTS
MAGNETIC MOMENTS
MAGNETIC SUSCEPTIBILITY
MANGANESE IONS
NEUTRON DIFFRACTION
OXIDES
OXYGEN
POLARIZATION
PYROCHLORE
SOLID OXIDE FUEL CELLS
SYNTHESIS
THERMAL EXPANSION
THERMAL GRAVIMETRIC ANALYSIS
X-RAY DIFFRACTION