Sol-gel synthesis, phase relationships, and oxygen permeation properties of Sr4Fe6-xCoxO13+delta (O <= x <= 3)

Sr4Fe6-xCoxO13+delta samples have been synthesized by a sol-gel procedure f or 0 less than or equal to x less than or equal to 3 and the influence of f iring temperature and procedure on the phase relationships has been investi gated systematically. For a synthesis temperature of 1000 degrees C, X-ray diffraction data reveal that the samples with x less than or equal to 1.8 a re single phase consisting of the intergrowth phase Sr4Fe6-xCoxO13+delta, w hile those with x>1.8 are composed of three phases - Sr4Fe6-xCoxO13+delta i ntergrowth phase, SrFe1-xCoxO3-delta perovskite phase, and Co3-xFexO4 spine l phase. Rietveld analysis of the X-ray diffraction data and thermogravimet ric analysis of the samples reveal that the fraction of the perovskite phas e increases as the synthesis temperature increases from 1000 to 1150 degree s C for x>1.8. For a given synthesis/annealing temperature, the sol-gel pro cedure favors a higher fraction of and higher solubility of Co in the inter growth phase compared to the conventional solid state synthesis. In the sin gle phase samples of the intergrowth oxide Sr4Fe6-xCoxO13+delta, the oxygen permeation flux at 900 degrees C decreases with increasing cobalt content x. On the other hand, the oxygen Aux increases with increasing x in the thr ee phase samples due to an increasing amount of the SrFe1-xCoxO3-delta pero vskite phase. (C) 2000 Elsevier Science B.V. All rights reserved.