The effects of Nb doping on the chemical stability of Ba0.5Sr0.5Co0.8Fe0.2O3 - delta based solid solutions under high oxygen partial pressure (p(O-2)) and CO2-containing atmospheres were studied. BSCF and Ba0.5Sr0.5Co0.9Nb0.1O3 - delta (BSCN) and Ba0.5Sr0.5Co0.8Fe0.1Nb0.1O3 (- delta) (BSCFN) were prepared and investigated by using TG-DTA analysis under p(O-2) = 1 and 10(-3) bar with or without CO2. The results showed that the Nb substitution effectively improved the chemical stability under high oxidation condition and also improved the CO2-tolerance of BSCF-based materials. (C) 2014 Elsevier B.V. All rights reserved.