Fine particle. strontium and iron substituted lanthanum gallates La0.4Sr0.6Ga1-yFeyO3-delta, and La0.6Sr0.4Gai-yFeyO3-delta, where y=0.4, 0:6, and 0.8, have been synthesized by a modified citrate method. The membranes were prepared by pressing the powders using a uniaxial pressing machine to form a disc (13 mm diameter, 1 mm thickness) and sintering at 1250-1380 degreesC for 10 h. Formation of these powders and membranes were confirmed by the X-ray powder diffraction and scanning electron microscopy. The membranes remained the cubic structure under the sintering temperature below 1400 degreesC with the above 90% of theoretical density. Oxygen permeabilities of the as high as 1.5 cm(3)/min cm(2) was obtained for LSGF4646 at 925 degreesC. (C) 2003 Elsevier Science B.V. All rights reserved.