title: Low viscosity and high attenuation in MgSiO3post-perovskite inferred from atomic-scale calculations.
abstract: This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO3post-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.
authors.affiliation: Unité Matériaux et Transformations, UMR/CNRS 8207, Université de Lille 1, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Goryaeva
authors.affiliation: Unité Matériaux et Transformations, UMR/CNRS 8207, Université de Lille 1, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Carrez
authors.affiliation: Unité Matériaux et Transformations, UMR/CNRS 8207, Université de Lille 1, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Cordier