Hopping and clustering of oxygen vacancies in SrTiO3 by anelastic relaxation

The complex elastic compliance s11,T of SrTiO3-d has been measured as a function of the O deficiency d<0.01. The two main relaxation peaks in the absorption are identified with hopping of isolated O vacancies over a barrier of 0.60 eV and reorientation of pairs of vacancies involving a barrier of 1 eV. The pair binding energy is 0.2 eV, and indications for additional clustering, possibly into chains, is found already at d~0.004. The anisotropic component of the elastic dipole of an O vacancy is Dlambda = 0.026. The possible role of electrostatic repulsion between vacancies in slowing the kinetics for their aggregation is discussed.