Local structure and oxygen ion dynamics in La doped ceria: 17O NMR study

The local order and oxygen dynamics in La doped ceria (LDC) has been studied by 17O NMR techniques. High resolution 17O MAS NMR spectra show several oxygen resonances which are assigned to the lattice sites with 0, 1 and 2 nearest neighbor (nn) La3+ ions. The site with 1 nn La contributes two different lines depending on the presence or absence of oxygen vacancy. The sites with 2 nn La ions are represented by one single line, which indicates that two neighboring La3+ ions always bind one vacancy. Spin-lattice relaxation (T1) measurements on static samples were carried out between 293 K and 1073 K. The temperature dependence of T1 has been interpreted assuming two independent relaxation paths. The relaxation below 600 K is assigned to the oxygen dynamics in the lattice without involving vacancy diffusion. The relaxation at a higher temperature is interpreted to be caused by the oxygen hopping between vacant and occupied sites.