Vacancy defect positron lifetimes in strontium titanate
  The results of positron annihilation lifetime spectroscopy measurements on undoped, electron irradiated, and Nb doped SrTiO3 single crystals are reported. Perfect lattice and vacancy defect positron lifetimes were calculated using two different first-principles schemes. The Sr vacancy defect related positron lifetime was obtained from measurements on Nb doped, electron irradiated, and vacuum annealed samples. Undoped crystals showed a defect lifetime component dominated by trapping to Ti vacancy related defects. 
R.A. Mackie, S. Singh, J. Laverock, S.B. Dugdale, and D.J. Keeble