Hopping and clustering of oxygen vacancies in SrTiO3

It is shown that O vacancies(V-O) in SrTiO3-delta With delta < 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 delta < 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: Delta lambda = 0.026. (C) 2009 Elsevier B.V. All rights reserved.