The experimental data for equilibrium oxygen content in double perovskite cobaltite Pr0.9Y0.1BaCo2O6-delta show that the incorporation of yttrium in place of praseodymium results in stabilization of the tetragonal structure in wide limits of oxygen pressure and temperature. The thermodynamic model calculations of defect formation reactions demonstrate that the doping is accompanied with enhanced electron and oxygen ion disordering. The observed properties combination is promising for the using of the yttrium modified cobaltite as a cathode in intermediate temperature SOFCs and a ceramic material for oxygen separation and storage. (C) 2016 Elsevier B.V. All rights reserved.