Modelling the effect of pressure on the critical shear stress of MgO single crystals

Abstract

We use a hierarchical multi-scale model to study the effect of high pressure on the critical shear stresses of MgO. The two main slip systems, ½<110>{110} and ½<110>{100} are considered. Based on a generalized Peierls-Nabarro model, we show that the core structure of ½<110> screw dislocations is strongly sensitive to pressure. Mostly planar and spread in {110} at ambient pressure, the core of screw dislocations tends to spread in {100} with increasing pressure. Subsequently, one observes an inversion of the easiest slip systems between 30 and 60 GPa. At high pressure, the plasticity of MgO single crystals is expected to be controlled by ½<110>{100} slip systems, except at high temperature where both slip systems become active. Pressure is also found to increase the critical resolved shear stresses and to shift the athermal temperature toward higher temperatures. Under high pressure, MgO is thus characterized by a significant lattice friction on both slip systems.

Two-phase deformation of lower mantle mineral analogs

“…Amodeo et al, 2012;Kraych et al, 2016;Girard et al, 2016). Here we find the strength contrast between NaMgF 3 and NaCl at pressures near 4 GPa and temperatures 200-400 • C to be ∼10.…”

“…Amodeo et al, 2012;Kraych et al, 2016;Merkel et al, 2003). For deformation in a two-phase system with large strength contrast, microstructure greatly influences rheology (e.g.…”

Dislocations and Plastic Deformation in MgO Crystals: A Review

“…A comparison between these observations and simulations using VPSC models indicate that such textures are compatible with slip on 1 ⁄2<110>{110} [252,253]. In the study of Amodeo and colleagues [261], the authors investigate the pressure sensitivity of dislocation cores in MgO from ambient up to 100 GPa hydrostatic P using the multi-scale modeling approach described Section 2. Due to the increase of P, the Illustration of polycrystalline MgO compression textures (IPF of the compression axis) at various pressure modeled using the CPFEM approach, starting from a random distribution of crystal orientations.…”

“…Screw dislocation core (relative displacement mapping) and CRSS evolution under hydrostatic pressure computed using the multiscale modeling approach of Amodeo and collaborators [23,261]. (a-d) Screw dislocation core structure from ambient up to 100 GPa pressure computed using the PNG model (see Section 2).…”

Materials under pressure

“…This is further complicated by the presence of defects-point defects, dislocations, and grain boundaries-in materials, and to the dependence of these defects on the class of material. The authors draw on examples from calculations on the pressure response to defect behavior in body-centered-cubic (bcc) metals, 35,36 and in ionic 37 and covalent systems to illustrate the wide variation possible. They extend this discussion to illustrate the contrasting behavior of two forms of MgSiO 3 , the perovskite 38 and the post-perovskite.…”