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Modeling defects and plasticity in MgSiO3 post-perovskite: Part 2-screw and edge [100] dislocations.

Goryaeva AM, Carrez P, Cordier P - Phys Chem Miner (2015)

Bottom Line: We show that despite a small tendency to core spreading in {011}, [100] screw dislocations glide very easily (Peierls stress of 1 GPa) in (010) where only Mg-O bonds are to be sheared.Whatever the planes, (010), (001) or {011}, edge dislocations are characterized by a wider core (of the order of 2b).The layered structure of post-perovskite results in a drastic reduction in lattice friction opposed to the easiest slip systems compared to perovskite.

View Article: PubMed Central - PubMed

Affiliation: Unité Matériaux et Transformations, UMR CNRS 8207, Université de Lille1, Bat C6, 59655 Villeneuve d'Ascq Cedex, France.

ABSTRACT

In this study, we propose a full atomistic study of [100] dislocations in MgSiO3 post-perovskite based on the pairwise potential parameterized by Oganov et al. (Phys Earth Planet Inter 122:277-288, 2000) for MgSiO3 perovskite. We model screw dislocations to identify planes where they glide easier. We show that despite a small tendency to core spreading in {011}, [100] screw dislocations glide very easily (Peierls stress of 1 GPa) in (010) where only Mg-O bonds are to be sheared. Crossing the Si-layers results in a higher lattice friction as shown by the Peierls stress of [100](001): 17.5 GPa. Glide of [100] screw dislocations in {011} appears also to be highly unfavorable. Whatever the planes, (010), (001) or {011}, edge dislocations are characterized by a wider core (of the order of 2b). Contrary to screw character, they bear negligible lattice friction (0.1 GPa) for each slip system. The layered structure of post-perovskite results in a drastic reduction in lattice friction opposed to the easiest slip systems compared to perovskite.

No MeSH data available.


Related in: MedlinePlus

Disregistry function S(x) and the [100] Burgers vector density ρ(x) of the stable screw dislocations (I) and (II) computed for the cation sublattice. Evaluated value of the dislocation core half-width ζ is given in the plot
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Fig4: Disregistry function S(x) and the [100] Burgers vector density ρ(x) of the stable screw dislocations (I) and (II) computed for the cation sublattice. Evaluated value of the dislocation core half-width ζ is given in the plot

Mentions: The shortest Burgers vector [100] is found to produce two possible geometries of stable screw dislocation cores. Figure 2 shows a visualization of these dislocations based on differential displacement (DD) maps. For screw dislocations, all displacements are parallel to the line and hence cannot be visualized in views parallel to this direction which are adapted to show the core. In DD maps, the relative displacement between neighboring atoms, which is produced by the dislocations and which is perpendicular to the plane of view, is represented by an arrow between those two atoms. The lengths of the arrows scale to the amplitude of the displacement vector. Both dislocations (I) and (II) exhibit pure screw cores without any edge component. The dislocation line (I) located at (∞, ±¼, 0) is characterized by a compact planar core with a little spreading in (011). The dislocation line (II) located at (∞, ±¼, ½) is very similar, but it spreads in (). In fact, these dislocations represent a mirror reflection of each other. Locations of the dislocation lines coincide with the positions of [100] screw axis 21 between two Mg atoms. Superposition of these elements creates a local structure along the dislocation line similar to the action of a 2 axis instead of the original 21 (Fig. 3). The dislocation cores tend to spread toward the empty trigonal channels located between Si- and Mg-layers. The spreading of the cores is limited by two Si-layers, and the distortion produced by the dislocation core notably affects interconnection of Mg-polyhedra only. Figure 4 shows the atomic disregistry S(x) along <011> corresponding to this [100] screw dislocation calculated for the cations sublattice. The Burgers vector density ρ(x) (derivative of the disregistry) is also presented. These functions are identical for dislocations (I) and (II). The evaluated half-width of the dislocation core ζ is 1.93 Å (Fig. 4).Fig. 2


Modeling defects and plasticity in MgSiO3 post-perovskite: Part 2-screw and edge [100] dislocations.

Goryaeva AM, Carrez P, Cordier P - Phys Chem Miner (2015)

Disregistry function S(x) and the [100] Burgers vector density ρ(x) of the stable screw dislocations (I) and (II) computed for the cation sublattice. Evaluated value of the dislocation core half-width ζ is given in the plot
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4643660&req=5

Fig4: Disregistry function S(x) and the [100] Burgers vector density ρ(x) of the stable screw dislocations (I) and (II) computed for the cation sublattice. Evaluated value of the dislocation core half-width ζ is given in the plot
Mentions: The shortest Burgers vector [100] is found to produce two possible geometries of stable screw dislocation cores. Figure 2 shows a visualization of these dislocations based on differential displacement (DD) maps. For screw dislocations, all displacements are parallel to the line and hence cannot be visualized in views parallel to this direction which are adapted to show the core. In DD maps, the relative displacement between neighboring atoms, which is produced by the dislocations and which is perpendicular to the plane of view, is represented by an arrow between those two atoms. The lengths of the arrows scale to the amplitude of the displacement vector. Both dislocations (I) and (II) exhibit pure screw cores without any edge component. The dislocation line (I) located at (∞, ±¼, 0) is characterized by a compact planar core with a little spreading in (011). The dislocation line (II) located at (∞, ±¼, ½) is very similar, but it spreads in (). In fact, these dislocations represent a mirror reflection of each other. Locations of the dislocation lines coincide with the positions of [100] screw axis 21 between two Mg atoms. Superposition of these elements creates a local structure along the dislocation line similar to the action of a 2 axis instead of the original 21 (Fig. 3). The dislocation cores tend to spread toward the empty trigonal channels located between Si- and Mg-layers. The spreading of the cores is limited by two Si-layers, and the distortion produced by the dislocation core notably affects interconnection of Mg-polyhedra only. Figure 4 shows the atomic disregistry S(x) along <011> corresponding to this [100] screw dislocation calculated for the cations sublattice. The Burgers vector density ρ(x) (derivative of the disregistry) is also presented. These functions are identical for dislocations (I) and (II). The evaluated half-width of the dislocation core ζ is 1.93 Å (Fig. 4).Fig. 2

Bottom Line: We show that despite a small tendency to core spreading in {011}, [100] screw dislocations glide very easily (Peierls stress of 1 GPa) in (010) where only Mg-O bonds are to be sheared.Whatever the planes, (010), (001) or {011}, edge dislocations are characterized by a wider core (of the order of 2b).The layered structure of post-perovskite results in a drastic reduction in lattice friction opposed to the easiest slip systems compared to perovskite.

View Article: PubMed Central - PubMed

Affiliation: Unité Matériaux et Transformations, UMR CNRS 8207, Université de Lille1, Bat C6, 59655 Villeneuve d'Ascq Cedex, France.

ABSTRACT

In this study, we propose a full atomistic study of [100] dislocations in MgSiO3 post-perovskite based on the pairwise potential parameterized by Oganov et al. (Phys Earth Planet Inter 122:277-288, 2000) for MgSiO3 perovskite. We model screw dislocations to identify planes where they glide easier. We show that despite a small tendency to core spreading in {011}, [100] screw dislocations glide very easily (Peierls stress of 1 GPa) in (010) where only Mg-O bonds are to be sheared. Crossing the Si-layers results in a higher lattice friction as shown by the Peierls stress of [100](001): 17.5 GPa. Glide of [100] screw dislocations in {011} appears also to be highly unfavorable. Whatever the planes, (010), (001) or {011}, edge dislocations are characterized by a wider core (of the order of 2b). Contrary to screw character, they bear negligible lattice friction (0.1 GPa) for each slip system. The layered structure of post-perovskite results in a drastic reduction in lattice friction opposed to the easiest slip systems compared to perovskite.

No MeSH data available.


Related in: MedlinePlus