Modeling defects and plasticity in MgSiO3 post-perovskite: Part 3-Screw and edge 001 dislocations

AM Goryaeva and P Carrez and P Cordier, PHYSICS AND CHEMISTRY OF MINERALS, 44, 521-533 (2017).

DOI: 10.1007/s00269-017-0879-0

In this study, we investigate the complex structure of 001 screw and edge dislocation cores in MgSiO3 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 1/2 < 101 > partials, while for the screw dislocations the < 100 > component reaches only 15%. Under applied stress, both 001(010) screw and edge dislocations behave similarly. Above the Peierls stress, the two partials glide together while keeping their stacking-fault widths (similar to 11 and similar to 42 angstrom for the screw and edge dislocations, respectively) constant. The Peierls stress opposed to the glide of 001(010) screw dislocations is 3 GPa, while that of edge dislocations is 33% lower. Relying on the observed characteristics of the dislocation cores, we estimate the efficiency of 001(010) dislocation glide under the P-T conditions relevant to the lowermost mantle and demonstrate that dislocation creep for this slip system would occur in the so-called athermal regime where lattice friction for the considered slip system vanishes when the temperature rises above the critical T-a value of similar to 2,000 K.

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