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Anisotropy of Earth's D″ layer and stacking faults in the MgSiO_3 post-perovskite phase

机译：钙钛矿后MgSiO_3相中地球D''层的各向异性和堆积断层

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摘要

The post-perovskite phase of (Mg,Fe)SiO_3 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.
机译：（Mg，Fe）SiO_3的钙钛矿后相被认为是地球最下层地幔（D''层）的主要矿物相。它的特性解释了与该层有关的许多地球物理观测结果，例如D''不连续性，其地形和该层内的地震各向异性。在这里，我们使用一种新颖的模拟技术，即第一原理元动力学，来识别钙钛矿和钙钛矿后相之间的一类低能多型堆叠-断层结构。元动力学轨迹确定涉及堆积断层形成的平面滑动是相变的最有利途径，也是钙钛矿和钙钛矿后塑性变形的可能机制。特别地，钙钛矿的预测滑动面为{010}（与实验一致），钙钛矿后的预测滑动面为{110}（与之前预期的{010}滑动面相反）。主导滑移平面定义了晶格的首选方向和纹理的弹性各向异性。钙钛矿后的{110}滑动面需要较小程度的晶格优先取向，以解释D''层中剪切波各向异性的地球物理观测结果。

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