Hopping and clustering of oxygen vacancies in SrTiO3

It is shown that O vacancies (VO) in SrTiO3-? with ?<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 VO are aggregated already at ?<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: View the MathML source.