Ba effect in doped Sr(Co0.8Fe0.2)O3-delta on the phase structure and oxygen permeation properties of the dense ceramic membranes

BaxSr1-xCo0.8Fe0.2O3-delta (x = 0 similar to 1.0) composite oxides were pre pared by a combined EDTA and citrate complexing method. The doping effect o f Ba on the phase structure, phase stability and oxygen permeation properti es of the mixed conductors was investigated with combined XRD, H-2-TPR, O-2 -TPD techniques and oxygen permeation studies. It was found that the perovs kite structure was sustained in the whole range of the oxygen activity inve stigated (0.21 similar to 10(-6) atm) when 0.3 less than or equal to x less than or equal to 0.5. But for the materials with a differed doping content of Ba (x = 0 similar to 0.1, 0.7 similar to 1.0), a phase transition was a ccompanied which was deleterious to the integrality of the membrane during operation. The relationship of phase structure and stability with tolerance factor was proposed. The doping of Ba in Sr(Co0.8Fe0.2)O3-delta could not lead to the improvement of these materials in the resisting of reduction, b ut the synergetic effect between cobalt and iron in the material was improv ed. Considerable high oxygen permeation rates were found for the BSCFO memb ranes in the whole range of Ba doping content. The Ba0.3Sr0.7Co0.8Fe0.2O3-d elta membrane had the highest oxygen permeation flux, (1.19 ml/cm(2) min fo r 1.50 mm thickness membrane at 850 degreesC), the lowest activation energy for oxygen transportation (37.8 KJ/mol at the temperature range of 731 deg reesC similar to 950 degreesC), and the lowest critical temperature for the change in the activation energy (731 degreesC). (C) 2001 Elsevier Science B.V. All rights reserved.