Study on the Redox Behavior and Reactive Oxygen Site of Reducible A₂B₂O₇ Composite Oxides

ABSTRACT: In this study, a series of reducible A₂B₂O₇ composite oxides was synthesized using a simple citric acid sol-gel method. Different characterization techniques were employed to reveal the essential factors affecting the redox properties and surface chemically adsorbed oxygen species of these compounds. The results indicate that the redox properties of ionic oxides of the A-site and B-site influence the redox behavior of the corresponding A₂B₂O₇ compounds, while the rigidity and looseness of the sub-crystal phase structure, as well as the lattice disorder degree, of these compounds affect the amount of surface chemisorbed oxygen. The type of sub-crystalline structure and lattice disorder are essential factors influencing the amount of chemisorbed oxygen species, with the order being disordered solid solution/disordered defect fluorite > pyrochlore > layered perovskite. Furthermore, it was found that the lattice disorder degree of Pr₂Zr₂O₇ and Tb₂Zr₂O₇ increases due to the complete reduction of Pr⁴⁺ or Tb⁴⁺ to Pr³⁺ and Tb³⁺ in a high-temperature reducing atmosphere (>600 °C). Similarly, disordered defect fluorite structures, such as Pr₂Ce₂O₇ and Tb₂Ce₂O₇, transform into rare-earth C-type crystalline structures in the same reducing atmosphere.