abstract
The total conductivity, Seebeck coefficient, thermal and chemical expansions, and steady-state oxygen permeability of Sr0.7Ce0.3Mn1-yCr3-delta (y = 0-0.5) with tetragonal perovskite structure were analyzed in the oxygen partial pressure range 10(-16) to 0.3 atm at 600-1270 K. The oxygen permeation fluxes, governed by both surface exchange kinetics and bulk ionic transport limited by low oxygen-vacancy concentration, are 10-30 times higher compared to (La,Sr)MnO3-delta. While the perovskite lattice of (Sr0.7Ce0.3)(1-x)MnO3-delta (x=0-0.05) is almost intolerant with respect to A-site cation deficiency, the stability limits of Sr0.7Ce0.3Mn1-yCryO3-delta reducing atmospheres are essentially unaffected by Cr doping and correspond to oxygen partial pressures of (0.4-1.5)x 10(-11) atm at 1223 K. The substitution of chromium for manganese decreases p-type electronic conduction predominant in the whole phase stability domain, suppresses chemical expansion on reducing P(02) due to lowering oxygen stoichiometry variations, but leads also to moderately higher thermal expansion. The electrical properties indicate strong hole trapping by chromium cations and progressive charge-carrier localization. The steady-state polarization studies of porous Sr0.7Ce0.3Mn0.9Cr0.1O3-delta electrodes in contact with two apatite-type silicate electrolytes, La10Si5AlO26.5 and La6.83Pr3Si4.5Fe1.5O26+delta showed a relatively poor electrochemical performance, which may be partly associated with microstructural degradation and cation interdiffusion between the cell components. (C) 2008 Elsevier B.V. All rights reserved.
keywords
OXIDE FUEL-CELLS; ELECTRICAL-PROPERTIES; OXYGEN PERMEABILITY; ELECTRONIC CONDUCTIVITY; TRANSPORT; NONSTOICHIOMETRY; MN; EXPANSION; MEMBRANES; CATHODES
subject category
Chemistry; Physics
authors
Yaremchenko, AA; Kovalevsky, AV; Kharton, VV
our authors
Aleksey Yaremchenko
Principal Researcher
Andrei Kavaleuski
Principal Researcher
Vladislav Kharton
Invited Principal Researcheracknowledgements
This work was supported by the FCT, Portugal (projects PTDC/CFM/64357/2006 and SFRH/BPD/15003/2004), and the MatSILC project (CEC, STREP 033410). Experimental assistance of Y.V. Pivak is gratefully acknowledged.