Institution: | a Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193, Aveiro, Portugal b Institute of Physicochemical Problems, Belarus State University, 14 Leningradskaya Str., 220050, Minsk, Belarus c Institute of Solid State Chemistry, Ural Division of RAS, 91 Pervomaiskaia Str., Ekaterinburg 620219, Russia d St. Petersburg Institute of Nuclear Physics RAS, Gatchina, 188350 Leningrad Region, Russia |
Abstract: | The maximum solid solubility of gallium in the perovskite-type La1−xSrxFe1−yGayO3−δ (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−δ in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7–16.0)×10−6 K−1 at 300–800 K and (19.3–26.7)×10−6 K−1 at 800–1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La1−xSrxFe1−yGayO3−δ (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−δ 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. |