Oxygen nonstoichiometry, thermal expansion and high-temperature electrical properties of layered NdBaCo2O5+delta and SmBaCo2O5+delta

abstract

Layered LnBaCo(2)O(5+delta) (La = Nd, Sm) with the cation-ordered double perovskite structure were synthesized by the solid-state reaction route and characterized by X-ray diffraction, thermogravimetric analysis and dilatometry. For NdBaCo2O5.73 and SmBaCo2O5.61 equilibrated with atmospheric oxygen at low temperatures, tetragonal and orthorhombic polymorphs were found to form, respectively. The oxygen content at 300-1300 K decreases with decreasing rare-earth cation size, whilst 8 variations and chemical contribution to the apparent thermal expansion in air are substantially lower compared to the disordered (Ln, A)CoO3-delta (A = Ca, Sr) analogues. The average thermal expansion coefficients are 23.1 x 10(-6) K-1 for NdBaCo2O5+delta and 20.8 x 10(-6) K-1 for SmBaCo2O5+delta at 300-1370 K and atmospheric oxygen pressure. These values are comparable to those of Bi2O3-based ionic conductors, but are incompatible with common electrolytes such as stabilized zirconia or doped ceria. The oxygen partial pressure dependencies of the total conductivity and Seebeck coefficient, studied in the P(O-2) range from 10(-10) to 1 atm, confirm predominant p-type electronic conductivity. (C) 2010 Elsevier Ltd. All rights reserved.

keywords

OXIDE FUEL-CELLS; CHEMISTRY; LN; CONDUCTIVITY; PEROVSKITES; CATHODES; CRYSTAL; PR; LA; SM

subject category

Materials Science

authors

Aksenova, TV; Gavrilova, LY; Yaremchenko, AA; Cherepanov, VA; Kharton, VV

our authors

acknowledgements

This work was financially supported in parts by RFBR grant no. 09-03-00620, Federal Agency for Science and Innovations of Russian Federation, Federal Agency for Education of Russian Federation, and the FCT, Portugal (project PTDC/CTM/64357/2006).

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