Periclase deforms more slowly than bridgmanite under mantle conditions.

Transport of heat from the interior of the Earth drives convection in the mantle, which involves the deformation of solid rocks over billions of years. The lower mantle of the Earth is mostly composed of iron-bearing bridgmanite MgSiO and approximately 25% volume periclase MgO (also with some iron). It is commonly accepted that ferropericlase is weaker than bridgmanite.

Ultimate mechanical properties of enstatite.

Unlabelled: The ultimate mechanical properties of MgSiO orthoenstatite (OEN), as characterized here by the ideal strengths, have been calculated under tensile and shear loadings using first-principles calculations. Both ideal tensile strength (ITS) and shear strength (ISS) are computed by applying homogeneous strain increments along high-symmetry directions ([100], [010], and [001]) and low index shear planes ((100), (010), and (001)) of the orthorhombic lattice. We show that the ultimate mechanical properties of OEN are highly anisotropic during tensile loading, with ITS ranging from 4.

A critical assessment of interatomic potentials for modelling lattice defects in forsterite Mg SiO from 0 to 12 GPa.

Unlabelled: Five different interatomic potentials designed for modelling forsterite Mg SiO are compared to and experimental data. The set of tested properties include lattice constants, material density, elastic wave velocity, elastic stiffness tensor, free surface energies, generalized stacking faults, neutral Frenkel and Schottky defects, in the pressure range  GPa relevant to the Earth's upper mantle. We conclude that all interatomic potentials are reliable and applicable to the study of point defects.

The role of diffusion-driven pure climb creep on the rheology of bridgmanite under lower mantle conditions.

The viscosity of Earth's lower mantle is poorly constrained due to the lack of knowledge on some fundamental variables that affect the deformation behaviour of its main mineral phases. This study focuses on bridgmanite, the main lower mantle constituent, and assesses its rheology by developing an approach based on mineral physics. Following and revising the recent advances in this field, pure climb creep controlled by diffusion is identified as the key mechanism driving deformation in bridgmanite.

Prediction of Mechanical Twinning in Magnesium Silicate Post-Perovskite.

The plastic properties of MgSiO post-perovskite are considered to be one of the key issues necessary for understanding the seismic anisotropy at the bottom of the mantle in the so-called D" layer. Although plastic slip in MgSiO post-perovskite has attracted considerable attention, the twinning mechanism has not been addressed, despite some experimental evidence from low-pressure analogues. On the basis of a numerical mechanical model, we present a twin nucleation model for post-perovskite involving the emission of 1/6 <110> partial dislocations.

Pure climb creep mechanism drives flow in Earth's lower mantle.

At high pressure prevailing in the lower mantle, lattice friction opposed to dislocation glide becomes very high, as reported in recent experimental and theoretical studies. We examine the consequences of this high resistance to plastic shear exhibited by ringwoodite and bridgmanite on creep mechanisms under mantle conditions. To evaluate the consequences of this effect, we model dislocation creep by dislocation dynamics.

Modeling defects and plasticity in MgSiO post-perovskite: Part 3-Screw and edge [001] dislocations.

In this study, we investigate the complex structure of [001] screw and edge dislocation cores in MgSiO post-perovskite at the atomic scale. Both [001] screw and edge dislocations exhibit spontaneous dissociation in (010) into two symmetric partials characterized by the presence of <100> component. In case of edge dislocations, dissociation occurs into ½<101> partials, while for the screw dislocations the <100> component reaches only 15%.

Screw-Dislocation-Induced Strengthening-Toughening Mechanisms in Complex Layered Materials: The Case Study of Tobermorite.

Nanoscale defects such as dislocations have a profound impact on the physics of crystalline materials. Understanding and characterizing the motion of screw dislocation and its corresponding effects on the mechanical properties of complex low-symmetry materials has long been a challenge. Herein, we focus on triclinic tobermorite, as a model system and a crystalline analogue of layered hydrated cement, and report for the first time how the motion of screw dislocation can influence the strengthening-toughening relationship, imparting brittle-to-ductile transitions.

Low viscosity and high attenuation in MgSiO post-perovskite inferred from atomic-scale calculations.

This work represents a numerical study of the thermal activation for dislocation glide of the [100](010) slip system in MgSiO 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.

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

In this study, we propose a full atomistic study of [100] dislocations in MgSiO post-perovskite based on the pairwise potential parameterized by Oganov et al. (Phys Earth Planet Inter 122:277-288, 2000) for MgSiO perovskite. We model screw dislocations to identify planes where they glide easier.

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

In this work, we examine the transferability of a pairwise potential model (derived for MgSiO perovskite) to accurately compute the excess energies of the generalized stacking faults (GSF, also called -surfaces) in MgSiO 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.

Modelling the rheology of MgO under Earth's mantle pressure, temperature and strain rates.

Plate tectonics, which shapes the surface of Earth, is the result of solid-state convection in Earth's mantle over billions of years. Simply driven by buoyancy forces, mantle convection is complicated by the nature of the convecting materials, which are not fluids but polycrystalline rocks. Crystalline materials can flow as the result of the motion of defects--point defects, dislocations, grain boundaries and so on.

Implications for plastic flow in the deep mantle from modelling dislocations in MgSiO3 minerals.

The dynamics of the Earth's interior is largely controlled by mantle convection, which transports radiogenic and primordial heat towards the surface. Slow stirring of the deep mantle is achieved in the solid state through high-temperature creep of rocks, which are dominated by the mineral MgSiO3 perovskite. Transformation of MgSiO3 to a 'post-perovskite' phase may explain the peculiarities of the lowermost mantle, such as the observed seismic anisotropy, but the mechanical properties of these mineralogical phases are largely unknown.