Material properties of perovskites in the quasi-ternary system LaFeO3-LaCoO3-LaNiO3

F. Tietz, I. Arul Raj, Q. Ma, S. Baumann, A. Mahmoud, R. P. Hermann

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Abstract

An overview is presented on the variation of electrical conductivity, oxygen permeation, and thermal expansion coefficient as a function of the composition of perovskites in the quasi-ternary system LaFeO3-LaCoO3-LaNiO3. Powders of thirteen nominal perovskite compositions were synthesized under identical conditions by the Pechini method. The powder X-ray diffraction data of two series, namely La(Ni0.5Fe0.5)1-xCoxO3 and LaNi0.5-xFexCo0.5O3, are presented after the powders had been sintered at 1100 °C for 6 h in air. The measurements revealed a rhombohedral structure for all compositions except LaNi0.5Fe0.5O3 for which 60% rhombohedral and 40% orthorhombic phase was found. The maximum DC electrical conductivity value of the perovskites at 800 °C was 1229 S cm-1 for the composition LaCoO3 and the minimum was 91 S cm-1 for the composition LaCo0.5Fe0.5O3. The oxygen permeation of samples with promising conductivities at 800 °C was one order of magnitude lower than that of La0.6Sr0.4Co0.8Fe0.2O3 (LSCF). The highest value of 0.017 ml cm-2 min-1 at 950 °C was obtained with LaNi0.5Co0.5O3. The coefficients of thermal expansion varied in the range of 13.2×10-6 K-1 and 21.9×10-6 K-1 for LaNi0.5Fe0.5O3 and LaCoO3, respectively. 57Fe Mössbauer spectroscopy was used as probe for the oxidation states, local environment and magnetic properties of iron ions as a function of chemical composition. The substitution had a great influence on the chemical properties of the materials.

Original languageEnglish
Pages (from-to)183-191
Number of pages9
JournalJournal of Solid State Chemistry
Volume237
DOIs
StatePublished - May 1 2016

Funding

The research leading to these results received funding from the European Union’s Seventh Framework Program ( FP7/2007–2013 ) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no. 256730 . The authors thank colleagues at ZEA-3, Forschungszentrum Jülich, for ICP-OES measurements, M. Ziegner (IEK-2, Forschungszentrum Jülich) for XRD measurements, and Prof. F. Grandjean for helpful discussions. A. Mahmoud acknowledges Forschungszentrum Jülich for an international postdoctoral grant. Work at Oak Ridge National Laboratory was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division .

Keywords

  • Electrical conductivity
  • Mössbauer spectroscopy
  • Oxygen permeation
  • Perovskites
  • Thermal expansion

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