The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms were studied in La1−xSrxGa1−xMgxO3−x (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that 71Ga, 25Mg and 17O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appeared exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO5/2-□-GaO5/2. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O5/6□1/6)6/2. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites was found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as was observed from both the motional narrowing of 17O NMR spectra and the 17O nuclear spin-lattice relaxation rate. The obtained results showed that two types of motion exist, a slow motion and a fast one. The former was a long-range diffusion whereas the latter was a local back and forth oxygen jumps between two adjacent anion sites. These sites were strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x <0.15.

Vacancy Ordering and Oxygen Dynamics in Oxide Ion Conducting La1−xSrxGa1−xMgxO3−x Ceramics: 71Ga, 25Mg and 17O NMR. A.Buzlukov, A.Trokiner, V.Kozhevnikov, S.Verkhovskii, A.Yakubovsky, I.Leonidov, A.Gerashenko, A.Stepanov, I.Baklanova, A.Tankeyev: Journal of Solid State Chemistry, 2011, 184[1], 36-43