Nonstoichiometry, thermal expansion and oxygen permeability of SmBaCo2 − xCuxO6 − δ

• Phase relations in pseudobinary SmBaCo2-xCuxO6-δ system were studied
• At 0 ≤ x ≤ 1.2, layered perovskites with orthorhombic and tetragonal structure form
• Thermal expansion and total conductivity decrease on Cu doping
• Doping increases oxygen vacancy concentration and oxygen permeability
• Copper additions promote chemical interaction with solid oxide electrolytes

Phase relationship analysis in the pseudobinary SmBaCo2 − xCuxO6 − δ system at 1000–1100 °С in air revealed the existence of solid solutions with the layered perovskite and 123-type structures, formed within the ranges of 0 ≤ x ≤ 1.2 and 1.5 ≤ x ≤ 2.0, respectively. The substitution of Cu2 + for Co3 +/4 + was found to induce phase transition from orthorhombic (space group Pmmm) into tetragonal (P4/mmm) polymorph at x > 0.1, and to increase oxygen deficiency studied by thermogravimetry and iodometric titration. The electrical conductivity and thermal expansion of Cu-substituted cobaltites decrease on doping, while the steady-state oxygen permeability exhibits an opposite trend, in correlation with the oxygen content variations. The average thermal expansion coefficient of SmBaCo1.4Cu0.6O6 − δ ceramics, where the level of ionic transport is comparable to that in most permeable cobaltite-based mixed conductors, is 16.9 × 10− 6 K− 1 at 25–1000 °С in air. At the same time, copper additions increase chemical reactivity of the materials with doped ceria electrolytes.