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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

Dependence of the Peierls stress σp related to the easiest screw dislocation glide in MgSiO3 perovskite (pv) and post-perovskite (ppv) phases on pressure corresponding to lower mantle. Values for the pv phase are taken from Hirel et al. (2014)
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Fig10: Dependence of the Peierls stress σp related to the easiest screw dislocation glide in MgSiO3 perovskite (pv) and post-perovskite (ppv) phases on pressure corresponding to lower mantle. Values for the pv phase are taken from Hirel et al. (2014)

Mentions: The atomic structure of [100] dislocations in MgSiO3 post-perovskite and its anisotropic lattice friction represent an issue of primary importance for understanding anisotropic plasticity of this mineral phase stable at the CMB. We find that glide of [100] dislocations is very easy in the (010) plane within the Mg–O layer. These results are in agreement with the TEM observations of [100](010) dislocations in deformed CaIrO3 post-perovskite analog (Walte et al.2007; Miyajima and Walte 2009). To go further and to highlight the importance of this effect, it is worth comparing with MgSiO3 perovskite (bridgmanite). A previous atomic scale study of MgSiO3 perovskite (Hirel et al. 2014) has shown that in this structure, lattice friction increases significantly over the pressure range of the lower mantle. In Hirel et al. (2014), the strategy was similar to the one used here, focusing on the easiest slip systems ([100](010) and [010](100) in bridgmanite) and employing the same potential model. Figure 10 compares the Peierls stresses of the easiest screw dislocations in bridgmanite as a function of pressure and in the post-perovskite. It is shown that the change of crystal structure which results in a layering is responsible for a drop in the lattice friction (considering the easiest slip systems of course). From a completely different perspective, our calculations support the suggestion from Ammann et al. (2010) (based on a theoretical study of anisotropic diffusion in post-perovskite) that the transition to the post-perovskite may be responsible for a weaker layer in the D″ layer.Fig. 10


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)

Dependence of the Peierls stress σp related to the easiest screw dislocation glide in MgSiO3 perovskite (pv) and post-perovskite (ppv) phases on pressure corresponding to lower mantle. Values for the pv phase are taken from Hirel et al. (2014)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4643660&req=5

Fig10: Dependence of the Peierls stress σp related to the easiest screw dislocation glide in MgSiO3 perovskite (pv) and post-perovskite (ppv) phases on pressure corresponding to lower mantle. Values for the pv phase are taken from Hirel et al. (2014)
Mentions: The atomic structure of [100] dislocations in MgSiO3 post-perovskite and its anisotropic lattice friction represent an issue of primary importance for understanding anisotropic plasticity of this mineral phase stable at the CMB. We find that glide of [100] dislocations is very easy in the (010) plane within the Mg–O layer. These results are in agreement with the TEM observations of [100](010) dislocations in deformed CaIrO3 post-perovskite analog (Walte et al.2007; Miyajima and Walte 2009). To go further and to highlight the importance of this effect, it is worth comparing with MgSiO3 perovskite (bridgmanite). A previous atomic scale study of MgSiO3 perovskite (Hirel et al. 2014) has shown that in this structure, lattice friction increases significantly over the pressure range of the lower mantle. In Hirel et al. (2014), the strategy was similar to the one used here, focusing on the easiest slip systems ([100](010) and [010](100) in bridgmanite) and employing the same potential model. Figure 10 compares the Peierls stresses of the easiest screw dislocations in bridgmanite as a function of pressure and in the post-perovskite. It is shown that the change of crystal structure which results in a layering is responsible for a drop in the lattice friction (considering the easiest slip systems of course). From a completely different perspective, our calculations support the suggestion from Ammann et al. (2010) (based on a theoretical study of anisotropic diffusion in post-perovskite) that the transition to the post-perovskite may be responsible for a weaker layer in the D″ layer.Fig. 10

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