Cobalt-free perovskite with the novel composition (Ba_(0.5)Sr_(0.5))(Fe_(0.80Cu_(0.2))O_(3-δ) (BSFCu) was synthesized via a sol-gel method and studied with respect to the crystallographic structure as well as the oxygen ionic and the electronic conductivity. In situ X-ray diffraction (XRD) was applied to investigate the thermal dilatation and the phase stability of the BSFCu at high and intermediate temperatures. Additionally, time-dependent oxygen permeation performance measurements were carried out for BSFCu and Co-based (Ba_(0.5)Sr_(0.5))(Co_(0.8)Fe_(0.2))O_(3-δ) membranes at 1023 K for 200 h. The BSFCu phase was found to be a cubic perovskite by XRD and transmission electron microscopy. The BSFCu membrane exhibits a very high oxygen permeation and electrical conductivity as compared to known perovskite membranes. The oxygen permeation of the BSFCu membrane maintains its value for 200 h at 1023 K unlike (Ba_(0.5)Sr_(0.5))(Co_(0.8)Fe_(0.2))O_(3-δ) whose oxygen flux was reduced by one-half during the same interval.
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