Polycrystalline “112” ordered oxygen deficient double perovskites YBaCo_2−xMe_xO_5+δ (Me = Fe, Cu, Ni) were synthesized by a glycerol-nitrate route with 0.0 ≤ x ≤ 0.7 for Me = Fe, 0.0 ≤ x ≤ 0.6 for Me = Cu and x = 0.1 for Me = Ni. The combined X-ray diffraction, electron microscopy and thermo-gravimetric studies show that all these oxides exhibit the a_p × a_p × 2a_p tetragonal structure (S.G. P4/mmm); moreover, the oxygen content increases continuously with x in the iron-substituted oxide YBaCo_2−xFe_xO_5+δ, whereas the opposite is observed for the copper phase YBaCo_2−xCu_xO_5+δ. This difference, which is due to the more electropositive character of Fe³⁺ compared to Cu²⁺, is hindered in the Ni²⁺ case due to its inability to accommodate the pyramidal coordination. The changes of the conductivity of these compounds versus temperature are closely related to their oxygen loss, in agreement with a defect structure model suggested earlier. Thermal expansion measurements prove the absence of phase transition in all oxides within the temperature range studied. The chemical compatibility of YBaCo_1.4Fe_0.6O_5+δ with the electrolyte Ce_0.8Sm_0.2O_2−δ is also demonstrated.