title: Anisotropy of Earth's D'' layer and stacking faults in the MgSiO3 post-perovskite phase.
abstract: The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D'' layer). Its properties explain numerous geophysical observations associated with this layer-for example, the D'' discontinuity, its topography and seismic anisotropy within the layer. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D'' layer.
authors.affiliation: Laboratory of Crystallography, Department of Materials, ETH Zurich, HCI G 515, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland. a.oganov@mat.ethz.ch
authors.forename: Artem R
authors.initials: AR
authors.lastname: Oganov
authors.forename: Roman
authors.initials: R
authors.lastname: Martonák
authors.forename: Alessandro
authors.initials: A
authors.lastname: Laio
authors.forename: Paolo
authors.initials: P
authors.lastname: Raiteri
authors.forename: Michele
authors.initials: M
authors.lastname: Parrinello