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Title: Chemical and structural changes in Ln{sub 2}NiO{sub 4+δ} (Ln=La, Pr or Nd) lanthanide nickelates as a function of oxygen partial pressure at high temperature

The chemical stability of lanthanide nickelates Ln{sub 2}NiO{sub 4+δ} (Ln=La, Pr or Nd) has been studied in the temperature range 25–1300 °C, either in air or at low pO{sub 2} (down to 10{sup −4} atm). Thermal gravimetry analysis (TGA) measurements coupled with X-ray diffraction (XRD) characterization have shown that all compounds retain their K{sub 2}NiF{sub 4}-type structure in these conditions, while remaining over-stoichiometric in oxygen up to 1000 °C. Only Nd{sub 2}NiO{sub 4+δ} starts to decompose into Nd{sub 2}O{sub 3} and NiO above 1000 °C, at pO{sub 2}=10{sup −4} atm. In addition, a careful analysis of the lanthanide nickelates structural features has been performed by in situ XRD, as a function of temperature and pO{sub 2}. For all compounds, a structural transition has been always observed in the temperature range 200–400 °C, in air or at pO{sub 2}=10{sup −4} atm. In addition, their cell volume did not vary upon the variation of the oxygen partial pressure. Therefore, these materials do not exhibit a chemical expansion in these conditions, which is beneficial for a fuel cell application as cathode layers. Additional dilatometry measurements have revealed that a temperature as high as 950 °C for Pr{sub 2}NiO{sub 4+δ} or 1100 °C formore » La{sub 2}NiO{sub 4+δ} and Nd{sub 2}NiO{sub 4+δ} has to be reached in order to begin the sintering of the material particles, which is of primary importance to obtain an efficient electronic/ionic conduction in the corresponding designed cathode layers. Besides, excellent matching was found between the thermal expansion coefficients of lanthanide nickelates and SOFC electrolytes such as 8wt% yttria stabilized zirconia (8YSZ) or Ce{sub 0.8}Gd{sub 0.2}O{sub 2−δ} (GDC), at least from 400 °C up to 1400 °C in air or up to 1200 °C at pO{sub 2}=10{sup −4} atm. - Graphical abstract: This study reports the good chemical stability of oxygen overstoichiometric Ln2NiO4+δ(Ln = La, Pr or Nd) at high temperatures (up to 1300 °C), eitherin air or at pO2down to 10-4 atm. In addition, these MSC cathode materials show a small chemical expansion as well as a good TEC compatibility with electrolyte materials (GDC or YSZ). - Highlights: • The structure of Ln2NiO4+δ compounds are studied vs. temperature and pO2 • Structural transitions are evidenced in air as well as in low pO2 atmosphere • The structural transitions do not significantly affect their TECs values • Up to 1200 °C, they show good chemical stability and no chemical expansion vs. pO2 • TECs of nickelates, 8YSZ and GDC are compared in air and in low pO2 atmosphere.« less
Authors:
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Publication Date:
OSTI Identifier:
22486736
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 228; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ATMOSPHERES; DILATOMETRY; GRAVIMETRY; LANTHANUM COMPOUNDS; LAYERS; NEODYMIUM OXIDES; NICKEL OXIDES; NICKELATES; PARTIAL PRESSURE; PRASEODYMIUM COMPOUNDS; PRESSURE DEPENDENCE; SINTERING; SOLID OXIDE FUEL CELLS; STOICHIOMETRY; TEMPERATURE DEPENDENCE; THERMAL EXPANSION; THERMAL GRAVIMETRIC ANALYSIS; X-RAY DIFFRACTION; YTTRIUM OXIDES; ZIRCONIUM OXIDES