New insights into the GdBaCo2O5+δ material: Crystal structure, electrical and electrochemical properties

• Different crystal structure is determined for GdBaCo2O5+δ depending on the oxygen content.
• A new superstructure with ap × 3ap × 2ap unit cell is observed for δ values close to 0.33.
• A total polarization resistance of 0.04 Ω cm2 is achieved at 650 °C for GdBaCo2O5+δ prepared in Ar.

Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) studies reveal that the crystal structure and microstructure of GdBaCo2O5+δ are highly influenced by the oxygen stoichiometry. In addition to layered-type ordering of the Ba and Gd atoms along the c-direction of the structure and location of anion vacancies within the (GdO)x planes giving a ap × ap × 2ap unit cell, two different perovskite related superstructures are observed. A superstructure with ap × 3ap × 2ap unit cell, probably due to extra ordering of the anion vacancies within the (GdO)x planes is formed for δ values close to 0.33 and a superstructure with √2ap × √2bp × 2ap unit cell associated to tilting of the CoO6 octahedra appears for the compound with δ values close to 1. Domain formation with perpendicular orientations of the unit cell occurs in crystals with orthorhombic symmetry of the structure. Physical properties of the aforementioned material, which is well known as a potential candidate of cathode for intermediate temperature solid oxide fuel cells, are likely to be strongly affected by its oxygen stoichiometry and therefore by its crystal structure and microstructure.