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A first-principles study of helium storage in oxides and at oxide–iron interfaces
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10.1063/1.4707944
/content/aip/journal/jap/111/11/10.1063/1.4707944
http://aip.metastore.ingenta.com/content/aip/journal/jap/111/11/10.1063/1.4707944

Figures

Image of FIG. 1.
FIG. 1.

(a)-(c) Formation energies for point defects in alumina (a) calculated using the PBE XC functional under Al-rich conditions, and calculated using the HSE06 hybrid functional under (b) Al-rich and (c) O-rich conditions, respectively. The line slopes correspond to the defect charge states according to Eq. (1) . (d)-(e) Binding energies of He interstitials to vacancies for (d) oxygen and (e) aluminum.

Image of FIG. 2.
FIG. 2.

Formation energies for point defects in titania calculated using (a) the PBE XC functional under Ti-rich conditions as well as the HSE06 hybrid functional under, (b) Ti-rich, and (c) O-rich conditions.

Image of FIG. 3.
FIG. 3.

Formation energies for point defects in yttria calculated using the PBE XC functional under (a) Y-rich and (b) O-rich conditions. (c) Binding energies of He interstitials to vacancies.

Image of FIG. 4.
FIG. 4.

Formation energies of He interstitials in various oxides as a function of the free volume at the interstitial site. Filled symbols indicate values at the respective equilibrium volumina.

Image of FIG. 5.
FIG. 5.

Migration barriers for He interstitials in several oxides as a function of the relative change in He–nearest neighbor separation. The inset shows the same data as a function of the relative change in the Voronoi volume of the He site. The light gray stripe is intended as a guide for the eye.

Image of FIG. 6.
FIG. 6.

Binding energy of He interstitial clusters in several oxides as well as iron (Fe data from Ref. 5 ) as a function of (a) the number of He atoms in the clusters and (b) the density of He interstitial sites in the host material.

Image of FIG. 7.
FIG. 7.

(a) and (b) Illustration of the Baker-Nutting orientation relationship. Projection of (a) rocksalt MgO and (b) body-centered cubic Fe along [001]. The latter is rotated by 45° about the [001] axis such that the and directions are parallel to each other. (c) Variation of interface energy as a function of the lateral displacement of the two crystals with respect to each other.

Image of FIG. 8.
FIG. 8.

Plane-averaged charge density and out-of-plane strain for the (a),(b) Fe—MgO and (c),(d) Fe—FeO—MgO interfaces as a function of position perpendicular to the interface plane. The colored spheres in the bottom panel indicate the atomic positions.

Image of FIG. 9.
FIG. 9.

Helium interstitial formation energies and their respective Voronoi volumina for the (a) Fe—MgO and (b) Fe—FeO—MgO interfaces as a function of position perpendicular to the interface. Helium atoms placed in the range indicated by the horizontal bars relax into the interface.

Image of FIG. 10.
FIG. 10.

Schematic energy landscape for He interstitial migration in an ODS steel. In the Fe matrix formation energies are high but migration barriers are low, while the opposite applies for the oxide particles. The smallest formation energies and thus the highest solubilities are predicted in the interface region. Strain fields can lead to gradients near the interface that depending on the sign of the strain field can either increase or decrease toward the interface.

Tables

Generic image for table
Table I.

Overview of computational parameters used in calculations of properties of the ideal bulk systems as well as point defects. Migration barrier calculations for Y2O3 and the rocksalt structured oxides were carried using the parameters given in brackets.

Generic image for table
Table II.

Migration barriers in eV for He interstitials in several oxides. Note that jump directions are approximate. : change in Voronoi volume of He site between initial state and saddle point normalized by volume of initial state; : change in He–nearest neighbor distance between initial state and saddle point normalized by initial neighbor distance.

Generic image for table
Table III.

Structural and electronic properties of Al2O3, TiO2, and Y2O3 from experiment and calculations. a, c: lattice parameters (Å), : rhombohedral angle (deg), , u: internal structural parameters, : band gap(eV), : electronic contribution to dielectric constant, : ionic contribution to dielectric constant, : static dielectric constant (sum of and ). The subscripts and indicate the dielectric constant perpendicular and parallel to the rhombohedral [111] axis (equivalent to the [0001] axis in the hexagonal setting), respectively. Note that for alumina the thermal band gap is reduced with respect to the optical gap (given here) due to polaronic effects (Ref. 49 ). Experimental data for alumina from Refs. 49 and 50 , for titania from Refs. 51–53 , and for yttria from Refs. 54 and 55 .

Generic image for table
Table IV.

Structural and electronic properties of yttrium aluminum oxides. Symbols as in Table III . Experimental data for YAP, YAG, and YAM from Refs. 57–59 , respectively.

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/content/aip/journal/jap/111/11/10.1063/1.4707944
2012-06-01
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: A first-principles study of helium storage in oxides and at oxide–iron interfaces
http://aip.metastore.ingenta.com/content/aip/journal/jap/111/11/10.1063/1.4707944
10.1063/1.4707944
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