abstract
The effects of doping the mixed-conducting (La,Sr)FeO3-delta system with Ce and Nb have been examined for the solid-solution series, La0.5-2xCexSr0.5+xFeO3-delta (x = 0-0.20) and La0.5-2ySr0.5+2yF1-yNbyO3-delta (y = 0.05-0.10). Mossbauer spectroscopy at 4.1 and 297 K showed that Ce4+ and Nb5+ incorporation suppresses delocalization of p-type electronic charge carriers, whilst oxygen nonstoichiometry of the Ce-containing materials increases. Similar behavior was observed for La0.3Sr0.7Fe0.90M0.10O3-delta at 923-1223 K by coulometric titration and thermogravimetry. High-temperature transport properties were studied with Faradaic efficiency (FE), oxygen-permeation, thermopower and total-conductivity measurements in the oxygen partial pressure range 10(-5) -0.5 atm. The hole conductivity is lower for the Ce- and Nb-containing perovskites, primarily as a result of the lower Fe4+ concentration. Both dopants decrease oxide-ion conductivity but the effect of Nb-doping on ionic transport is moderate and ion-transference numbers are higher with respect to the Nb-free parent phase, 2.2 x 10(-3) for La0.3Sr0.7Fe0.9Nb0.1O3-delta cf. 1.3 x 10(-3) for La0.5Sr0.5FeO3-delta at 1223 K and atmospheric oxygen pressure. The average thermal expansion coefficients calculated from dilatometric data decrease on doping, varying in the range (19.0-21.2) x 10(-6) K-1 at 780-1080 K. (c) 2006 Elsevier Masson SAS. All rights reserved.
keywords
MOSSBAUER-SPECTRA; LA1-XSRXFEO3-DELTA MEMBRANES; CHARGE DISPROPORTIONATION; ELECTRICAL-CONDUCTIVITY; OXYGEN STOICHIOMETRY; MIXED CONDUCTIVITY; THERMAL-EXPANSION; NONSTOICHIOMETRY; PERMEATION; STABILITY
subject category
Chemistry; Physics
authors
Kharton, VV; Waerenborgh, JC; Kovalevsky, AV; Mather, GC; Viskup, AP; Patrakeev, MV; Gaczynski, P; Yaremchenko, AA; Samakhval, VV
our authors
Aleksey Yaremchenko
Principal Researcher
Andrei Kavaleuski
Principal Researcher