Abstract
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 ½<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 (~11 and ~42 Å 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 Ta value of ~2,000 K.
Highlights
One of the most prominent features of the D′′ layer is the observation of well-developed seismic anisotropy (Vinnik et al 1989; Lay et al 1998; Panning and Romanowicz 2004)
We investigate in detail the complex atomic structure of dissociated [001] screw and edge dislocations in MgSiO3 post-perovskite and the opposed lattice friction described through the Peierls stress
The atomic structure of the relaxed screw dislocation core is illustrated in Fig. 2 where the stacking fault between the two partials can be clearly distinguished
Summary
One of the most prominent features of the D′′ layer is the observation of well-developed seismic anisotropy (Vinnik et al 1989; Lay et al 1998; Panning and Romanowicz 2004). Linking crystal plasticity to the development of CPO and seismic anisotropy requires information on slip systems activities (Wenk et al 2011). Indirect evidence of easy slip systems derived from the CPO observed during ultrahigh pressure experiments on MgSiO3 provides conflicting results (Merkel et al 2007; Miyagi et al 2010). Based on the TEM observations of dislocations in C aIrO3, the importance of [100](010) system seems well established; experimental evidence of deformation mechanisms along [010] and [001] directions in CaIrO3 is still scarce (Miyajima et al 2006; Miyajima and Walte 2009). First-principles studies indicate that anisotropic character of elasticity
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