Abstract
This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO3 post-perovskite (Mg-ppv) at 120 GPa. We propose an approach based on a one-dimensional line tension model in conjunction with atomic-scale calculations. In this model, the key parameters, namely, the line tension and the Peierls barrier, are obtained from density functional theory calculations. We find a Peierls stress σp = 2.1 GPa and a line tension Γ = 9.2 eV/Å, which lead to a kink-pair enthalpy (under zero stress) of 2.69 eV. These values confirm that this slip system bears a very low lattice friction because it vanishes for temperatures above approximately 500 K under mantle conditions. In the Earth’s mantle, high-pressure Mg-ppv silicate is thus expected to become as ductile as ferropericlase. These results confirm the hypothesis of a weak layer in the D″ layer where Mg-ppv is present. Easy glide along [100](010) suggests strong preferred orientations with (010) planes aligned. Highly mobile [100] dislocations are also likely to respond to stresses related to seismic waves, leading to energy dissipation and strong attenuation.
Highlights
In bridgmanite, Hirel et al.[18] showed that lattice friction increases monotonically throughout the lower mantle to reach, in the lowermost mantle, values of approximately 15 GPa
We present a theoretical study based on full atomistic modelling of plastic deformation, demonstrating easy glide of [100](010) dislocations in MgSiO3 post-perovskite (Mg-ppv) at finite temperature and strain rate of the lowermost mantle
density functional theory (DFT) represents high accuracy calculations, we employ a pairwise potential to compute the minimum energy path (MEP) between two stable cores associated with dislocation glide in (010) and to carefully investigate finite size effects
Summary
Hirel et al.[18] showed that lattice friction increases monotonically throughout the lower mantle to reach, in the lowermost mantle, values of approximately 15 GPa. Shearing the structure parallel to the structural layering is much easier: lattice friction opposed to the glide of [100] screw dislocations in the (010) plane is one order of magnitude lower than that in (001). This is the reason why we focus on this slip system in the present study. We present a theoretical study based on full atomistic modelling of plastic deformation, demonstrating easy glide of [100](010) dislocations in MgSiO3 post-perovskite (Mg-ppv) at finite temperature and strain rate of the lowermost mantle
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
