An ab initio study of the effect of charge localization on oxygen defect formation and migration energies in magnesium oxide

Abstract

Plane-wave density functional theory was used to study the properties of oxygen vacancies and interstitials, with different charge states, in MgO. The calculated properties were the relaxed configurations, the Frenkel defect formation energies and the energies of the migration barriers, and all properties were found to be strongly dependent on the defect charge state. The lowest energy configuration of the O 2− interstitial was found to be the cube centre; however, the O − and O 0 interstitials formed dumb-bell configurations. The Frenkel defect energies were also strongly dependent on the defect charge, with the neutral pair energy calculated to be 3 eV lower than the doubly charged Frenkel pair defect energy. The migration barriers of the oxygen vacancies were found to increase as the net charge of the oxygen vacancies decreased, which suggests that vacancies with trapped electrons are much less mobile than the F 2+ vacancies modelled by classical potentials. The migration of the oxygen interstitials showed particularly interesting behaviour. The O 0 interstitial was found to have a higher migration barrier than the O 2− interstitial but a very low barrier (0.06 eV) was found for the O − interstitial. The results have significant implications for the reliability of classical radiation damage simulations.

Diffusion of aluminium in MgO from first principles

“…Only the oxygen migration enthalpy still significantly increases with increasing supercell-size at the highest pressure-but still only by about 5 %. Again, these migration enthalpies are in good agreement with previous ab initio simulations (Gilbert et al 2007;Karki and Khanduja 2006;De Vita et al 1992;Mulroue and Duffy 2001) and the interested reader is referred to our recent review (Ammann et al 2010a) for further comparisons and details.…”

Damage processes in MgO irradiated with medium-energy heavy ions

“…In particular, some computational works have been performed for determining the defect energetics in MgO, using classical methods with selected empirical potentials [4][5][6]25] but also ab initio techniques such as the density functional theory [26][27][28]. All studies point out that (Mg and O) vacancies are immobile in MgO at RT, in terms of thermodynamic considerations, with migration energies of a few electronvolts.…”

“…This is particularly true for point defects, which have been demonstrated to be predominantly formed during collision cascades [4,5,25]. For instance, migration barrier values of 0.32 eV and 0.40 eV for O and Mg single-interstitials [4,5,25] and between 0.06, 0.33 and 1.04 eV for O À , O 2À and O 0 single-interstitials [28] were computed. In [4,5,25], di-interstitials and tri-interstitials were also found to be mobile at RT, but the migration barrier increases with the cluster size making them immobile at RT, except for the peculiar hexa-interstitial cluster with a diffusion barrier of 0.24 eV.…”

Ab initiostudy of intrinsic defects in zirconolite

“…It has been shown recently that trapping of holes and electrons at defects in MgO has a significant effect on their properties. 5 The long timescale durability of the material will depend on the evolution of the microstructure over periods of hundreds or even thousands of years, well beyond the timescale of experimental measurements. A detailed understanding of the properties of defects is, therefore, a necessary starting point for the prediction of the long-term durability of the encapsulating ceramics.…”