The maximum solid solubility of Ga in the perovskite-type La1-xSrxFe1-yGayO3-δ (x = 0.40–0.80; y = 0 to 0.60) was found to vary in the approximate range y = 0.25–0.45, decreasing when x increased. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction 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 decreased with Ga additions. The average thermal expansion coefficients were in the range (11.7–16.0) x 10-6/K at 300–800K and (19.3–26.7) x 10-6/K at 800 to 1100K. At O partial pressures close to atmospheric air, the O permeation fluxes through La1-xSrxFe1-yGayO3-δ (x = 0.7–0.8; y = 0.2–0.4) membranes were determined by the bulk ambipolar conductivity; the limiting effect of the O surface exchange was found negligible. Decreasing Sr and Ga concentrations led to a greater role of the exchange processes. As for many other perovskite systems, the O ionic conductivity of La1-xSrxFe1-yGayO3-δ increased with Sr content up to x = 0.70 and decreased on further doping, probably due to association of O vacancies. Incorporation of moderate amounts of Ga into the B sub-lattice results in increasing structural disorder, higher ionic conductivity at below 1170K, and lower activation energy for the ionic transport.

Perovskite-Like System (Sr,La)(Fe,Ga)O3-δ - Structure and Ionic Transport under Oxidizing Conditions. V.V.Kharton, A.L.Shaulo, A.P.Viskup, M.Avdeev, A.A.Yaremchenko, M.V.Patrakeev, A.I.Kurbakov, E.N.Naumovich, F.M.B.Marques: Solid State Ionics, 2002, 150[3-4], 229-43