The structural and electronic properties of O vacancy (VO) defects in cubic and antiferrodistortive phases of bulk SrTiO3 were investigated by using results from first principles pseudopotential calculations. By systematically increasing the super-cell size from 40 to 320 atoms, it was shown that large super-cells were necessary to investigate the structural energetics of this seemingly simple defect properly. With the increase in the super-cell size, the formation energy of VO decreased by ~1.3eV due to long-ranged relaxations, and the character of the defect wave function changed from a deep to a shallow level. Calculations indicated that presence of VO decreased the relative stability of the antiferrodistortive phase over the cubic phase, consistent with recent experimental results, which find a lowering of the antiferrodistortive-cubic transition temperature in samples with higher VO concentrations.

Structural and Electronic Properties of Oxygen Vacancies in Cubic and Antiferrodistortive Phases of SrTiO3. J.P.Buban, H.Iddir, S.Öğüt: Physical Review B, 2004, 69[18], 180102 (4pp)