Hopping and clustering of oxygen vacancies in

It is shown that O vacancies ( V O ) in SrTiO 3 − δ with δ < 0.01 give rise to at least three anelastic relaxation processes associated with hopping of isolated vacancies (activation energy of 0.60 eV), reorientation of pairs (0.97 eV) and formation/dissolution of pairs and other clusters. Most of the V O are aggregated already at δ < 0.01 , so explaining why an activation energy of 1 eV is generally found in experiments probing the O mobility. The anelastic spectra are well interpreted in terms of a model taking into account the formation of pairs and chains of length ≤ 4 , whose concentrations are calculated with a method based on the construction of an approximated grand-partition function. The anisotropic component of the elastic dipole of an isolated O vacancy is rather small: Δ λ = 0.026 .