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The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo₂O 5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo₂O 5+δ double perovskite was obtained by annealing cubic A-site cation disordered La 0.5 Ba 0.5 CoO 3-δ perovskite at 1100 °C in N₂. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo₂O 5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N₂ and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo₂O 5+δ was demonstrated. La 0.5 Ba 0.5 CoO 3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo₂O 5+δ is metastable with respect to La 0.5 Ba 0.5 CoO 3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La 0.5 Ba 0.5 CoO 3-δ resulting in a higher electrical conductivity relative to LaBaCo₂O 5+δ . The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior.

Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo2O5+δ Double Perovskite