Oxygen vacancy diffusion in bulk SrTiO3 from density functional theory calculations

Abstract

Point defects and their diffusion contribute significantly to the properties of perovskite materials. However, even for the prototypical case of oxygen vacancies in SrTiO 3 (STO), the predictions of oxygen vacancy activity vary widely. Here we present a comprehensive and systematic study of the diffusion barriers for this material. We use density functional theory (DFT) and assess the role of different supercell sizes, density functionals, and charge states. Our results show that vacancy-induced octahedral rotations, which are limited by the boundary conditions of the supercell, can significantly affect the computed oxygen vacancy diffusion energy barrier. In addition, we find that the diffusion energy barrier of a charged oxygen vacancy is lower than that of a neutral one. This difference is magnified in small supercells. We find that with increasing supercell size, the effects on the migration energy barrier of the oxygen vacancy charge state, the type of DFT exchange and correlation functional is diminishing, and all migration energy barriers of DFT prediction asymptote to a range of 0.39-0.49 eV, which is smaller than the reported experimental values. This work provides important insight and guidance that should be considered for investigations of point defect diffusion in perovskite materials and in oxide superlattices.

Ab initio description of oxygen vacancies in epitaxially strained $$\hbox {SrTiO}_{{3}}$$ at finite temperatures

“…These results appear to be in agreement with the scarce experimental data that is available for compressive biaxial strains 37 but in apparent disagreement with previous DFT results reported by Al-Hamadany et al 38 . The reasons for the disagreements between our theoretical NEB estimations and analogous computational results previously reported 38 could be the use of different exchange-correlation energy functionals and simulation supercells, which are known to affect the description of polar and antiferrodistortive oxygen octahedral distortions in functional oxide perovskites 47 , 79 . In order to fully test the reliability of our zero-temperature NEB results, we performed complementary ab initio molecular dynamics (AIMD) simulations in which lattice thermal excitations are fully taken into account and no particular diffusion path needs to be guessed 59 .…”

“…For integrations within the Brillouin zone (BZ), we used a -centered -point grid of for the 20-atoms simulation cell and scaled it conveniently to maintain an equivalent -point density for the rest of cases. All oxygen vacancies were assumed to be neutrally charged and non-magnetic ( ) as in previous DFT studies this configuration has been shown to render the lowest energy for bulk off-stoichiometric 9 , 47 , 48 .…”

“…Ab initio nudged-elastic band (NEB) calculations 58 were performed to estimate the activation energy for diffusion in expitaxially strained (001) at zero temperature. Our NEB calculations were performed for reasonably large or supercells containing several tens of atoms 47 . We used -point grids of or and an energy plane-wave cut-off of 650 eV.…”

Oxygen Diode Formed in Nickelate Heterostructures by Chemical Potential Mismatch

“…V O formation energies of BTO, [55,56] LAO, [57,58] and STO [59][60][61][62][63][64] are much greater than that of LNO. Therefore, one would expect that the V O would form preferentially in the underlying LNO layer rather than in the capping layers.…”

“…It is worth noting that the migration energies of our capping layers are lower than that of LNO (Table I), [35,56,57,59,65] facilitating oxygen diffusion out of the LNO layer, resulting in oxygen deficiency in LNO. STO has the smallest migration energy, thus, it is not too surprising to see that the largest valence and lattice volume changes in LNO occur upon capping with STO (see Figure 1 and Figure 3).…”