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Modeling defects and plasticity in MgSiO3 post-perovskite: Part 1-generalized stacking faults.

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

Bottom Line: In this work, we examine the transferability of a pairwise potential model (derived for MgSiO3 perovskite) to accurately compute the excess energies of the generalized stacking faults (GSF, also called γ-surfaces) in MgSiO3 post-perovskite.All calculations have been performed at 120 GPa, a pressure relevant to the D″ layer.Our results are in agreement with previous ab initio calculations.

View Article: PubMed Central - PubMed

Affiliation: Unité Matériaux et Transformations - UMR CNRS 8207 - Bat C6, Université Lille 1, 59655 Villeneuve d'Ascq Cedex, France.

ABSTRACT

In this work, we examine the transferability of a pairwise potential model (derived for MgSiO3 perovskite) to accurately compute the excess energies of the generalized stacking faults (GSF, also called γ-surfaces) in MgSiO3 post-perovskite. All calculations have been performed at 120 GPa, a pressure relevant to the D″ layer. Taking into account an important aspect of crystal chemistry for complex materials, we consider in detail all possible locations of slip planes in the post-perovskite structure. The γ-surface calculations emphasize the easiness of glide of slip systems with the smallest shear vector [100] and of the [001](010) slip system. Our results are in agreement with previous ab initio calculations. This validates the use the chosen potential model for further full atomistic modeling of dislocations in MgSiO3 post-perovskite.

No MeSH data available.


Related in: MedlinePlus

2D projections of γ-surfaces (in J/m2) computed in this study for (001) (a, b), (010) (c, d), (011) (e–g), (110) (h–j) and (100) (k) slip planes. The corresponding shear levels are given on each plot. Easy slip directions are highlighted with green arrows
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Fig3: 2D projections of γ-surfaces (in J/m2) computed in this study for (001) (a, b), (010) (c, d), (011) (e–g), (110) (h–j) and (100) (k) slip planes. The corresponding shear levels are given on each plot. Easy slip directions are highlighted with green arrows

Mentions: Previous ab initio studies of GSF in MgSiO3 post-perovskite provided only γ-lines (Carrez et al. 2007; Metsue and Tsuchiya 2013). In this work, full γ-surfaces are calculated for all possible slip planes and cutting levels. The shape of the obtained γ-surfaces clearly reflects the symmetry of the structure in a given glide plane for all configurations considered in this work (Fig. 3a–k). In agreement with the Cmcm space group, each γ-surface exhibits a mirror plane m perpendicular to the [100] and [001] directions. Due to the C-lattice, ½[110] translation vector is clearly seen in (001) and (110) γ-surfaces (Fig. 3a, b, h–j) such as all energy minimum valleys and maximum peaks are translated by ½ <110>. For (010) with z010 = 0.7 and (110) with z110 = 0.65 γ-surfaces, there are metastable stacking faults (Fig. 3c, h) whose presence is not caused by additional translation vectors of the lattice but by the favorable atomic arrangement in these configurations of faulted crystals. In case of (010), the stacking fault is located exactly in the middle of the γ-surface (Fig. 3c) and corresponds to a high-symmetry configuration where atoms are arranged in such a way that slip and unslip halfcrystals represent a mirror reflection of each other (due to the superposition of plane n010 and ½<101> shear component). For the (110) plane (Fig. 3h), stacking faults are centered with respect to [001] and disposed at 1/3[110] with ½<110> periodicity. Rigid shear by 1/3[110] results in a stacking fault structure where Si-octahedra are connected by corners instead of edges along the slip plane. This geometry reproduces the faulted structure related to post-perovskite–perovskite transformation previously described by (Oganov et al. 2005). Additional shear by ½[001] allows to optimize location of Mg atoms while keeping the same specific arrangement of Si close to the slip plane. Presence of metastable stacking faults in the middle of γ-surfaces may indicate simultaneous presence of ½[100] and ½[001] components for dislocations lying on (010) as well as 1/3[110] and ½[001] components for dislocations related to (110) as it is shown with arrows on Fig. 3c, h. Among all examined γ-surfaces, the (010) plane with z010 = 0.7 (Fig. 3c) is characterized by the lowest excess energies, while the highest energy barriers are observed for (100) and (001) at z001 = 0.47 along the longest [010] direction (Table 3; Fig. 3a, k).Fig. 3


Modeling defects and plasticity in MgSiO3 post-perovskite: Part 1-generalized stacking faults.

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

2D projections of γ-surfaces (in J/m2) computed in this study for (001) (a, b), (010) (c, d), (011) (e–g), (110) (h–j) and (100) (k) slip planes. The corresponding shear levels are given on each plot. Easy slip directions are highlighted with green arrows
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig3: 2D projections of γ-surfaces (in J/m2) computed in this study for (001) (a, b), (010) (c, d), (011) (e–g), (110) (h–j) and (100) (k) slip planes. The corresponding shear levels are given on each plot. Easy slip directions are highlighted with green arrows
Mentions: Previous ab initio studies of GSF in MgSiO3 post-perovskite provided only γ-lines (Carrez et al. 2007; Metsue and Tsuchiya 2013). In this work, full γ-surfaces are calculated for all possible slip planes and cutting levels. The shape of the obtained γ-surfaces clearly reflects the symmetry of the structure in a given glide plane for all configurations considered in this work (Fig. 3a–k). In agreement with the Cmcm space group, each γ-surface exhibits a mirror plane m perpendicular to the [100] and [001] directions. Due to the C-lattice, ½[110] translation vector is clearly seen in (001) and (110) γ-surfaces (Fig. 3a, b, h–j) such as all energy minimum valleys and maximum peaks are translated by ½ <110>. For (010) with z010 = 0.7 and (110) with z110 = 0.65 γ-surfaces, there are metastable stacking faults (Fig. 3c, h) whose presence is not caused by additional translation vectors of the lattice but by the favorable atomic arrangement in these configurations of faulted crystals. In case of (010), the stacking fault is located exactly in the middle of the γ-surface (Fig. 3c) and corresponds to a high-symmetry configuration where atoms are arranged in such a way that slip and unslip halfcrystals represent a mirror reflection of each other (due to the superposition of plane n010 and ½<101> shear component). For the (110) plane (Fig. 3h), stacking faults are centered with respect to [001] and disposed at 1/3[110] with ½<110> periodicity. Rigid shear by 1/3[110] results in a stacking fault structure where Si-octahedra are connected by corners instead of edges along the slip plane. This geometry reproduces the faulted structure related to post-perovskite–perovskite transformation previously described by (Oganov et al. 2005). Additional shear by ½[001] allows to optimize location of Mg atoms while keeping the same specific arrangement of Si close to the slip plane. Presence of metastable stacking faults in the middle of γ-surfaces may indicate simultaneous presence of ½[100] and ½[001] components for dislocations lying on (010) as well as 1/3[110] and ½[001] components for dislocations related to (110) as it is shown with arrows on Fig. 3c, h. Among all examined γ-surfaces, the (010) plane with z010 = 0.7 (Fig. 3c) is characterized by the lowest excess energies, while the highest energy barriers are observed for (100) and (001) at z001 = 0.47 along the longest [010] direction (Table 3; Fig. 3a, k).Fig. 3

Bottom Line: In this work, we examine the transferability of a pairwise potential model (derived for MgSiO3 perovskite) to accurately compute the excess energies of the generalized stacking faults (GSF, also called γ-surfaces) in MgSiO3 post-perovskite.All calculations have been performed at 120 GPa, a pressure relevant to the D″ layer.Our results are in agreement with previous ab initio calculations.

View Article: PubMed Central - PubMed

Affiliation: Unité Matériaux et Transformations - UMR CNRS 8207 - Bat C6, Université Lille 1, 59655 Villeneuve d'Ascq Cedex, France.

ABSTRACT

In this work, we examine the transferability of a pairwise potential model (derived for MgSiO3 perovskite) to accurately compute the excess energies of the generalized stacking faults (GSF, also called γ-surfaces) in MgSiO3 post-perovskite. All calculations have been performed at 120 GPa, a pressure relevant to the D″ layer. Taking into account an important aspect of crystal chemistry for complex materials, we consider in detail all possible locations of slip planes in the post-perovskite structure. The γ-surface calculations emphasize the easiness of glide of slip systems with the smallest shear vector [100] and of the [001](010) slip system. Our results are in agreement with previous ab initio calculations. This validates the use the chosen potential model for further full atomistic modeling of dislocations in MgSiO3 post-perovskite.

No MeSH data available.


Related in: MedlinePlus