resumo
The maximum solid solubility of gallium in the perovskite-type La1-xSrxFe1-yGayO3-delta (x=0.40-0.80; y=0-0.60) was found to vary in the approximate range y = 0.25-0.45, decreasing when x increases. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction (XRD) and neutron diffraction and identified as cubic. Doping with Ga results in increasing unit cell volume, while the thermal expansion and total conductivity of (La,Sr)(Fe,Ga)O3-delta in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7-16.0) x 10(-6) K-1 at 300-800 K and (19.3-26.7) x 10(-6) K-1 at 800-1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La1-xSrxFe1-yGayO3-delta (x=0.7-0.8; y=0.2-0.4) membranes are determined by the bulk ambipolar conductivity; the limiting effect of the oxygen surface exchange was found negligible. Decreasing strontium and gallium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La1-xSrxFe1-yGayO3-delta increases with strontium content up to x=0.70 and decreases on further doping, probably due to association of oxygen vacancies. Incorporation of moderate amounts of gallium into the B sublattice results in increasing structural disorder, higher ionic conductivity at temperatures below 1170 K, and lower activation energy for the ionic transport. (C) 2002 Elsevier Science B.V All rights reserved.
palavras-chave
DOPED LANTHANUM GALLATE; HIGH-TEMPERATURE; ELECTRONIC CONDUCTION; NEUTRON-DIFFRACTION; OXYGEN-TRANSPORT; OXIDES; FE; STRONTIUM; MEMBRANES; CRYSTAL
categoria
Chemistry; Physics
autores
Kharton, VV; Shaulo, AL; Viskup, AP; Avdeev, M; Yaremchenko, AA; Patrakeev, MV; Kurbakov, AI; Naumovich, EN; Marques, FMB
nossos autores
Aleksey Yaremchenko
Investigador Principal
Fernando Manuel Bico Marques
Professor Catedrático