The defect chemistry of lanthana–ceria mixed oxides by MASNMR

Detailed 17O and 139La MASNMR studies have been made of the mixed lanthanide system La2O3–CeO2. Specifically, it has been found that there is a defect chemistry dominated by the formation of anion vacancies in the lattice. By carrying out work at several calcination temperatures good evidence for an anion defect-cation association energy of 0.26 eV was provided and is close to values predicted in theoretical studies. For the first time evidence is provided which conclusively shows the anions are mobile in the structure, that local ordering occurs and that there is dramatic structural rearrangement around each vacancy. Data are interpreted in view of well-known cubic and hexagonal structural rearrangements in the system.