Oganov Artem R, Martonák Roman, Laio Alessandro, Raiteri Paolo, Parrinello Michele
Laboratory of Crystallography, Department of Materials, ETH Zurich, HCI G 515, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
Nature. 2005 Dec 22;438(7071):1142-4. doi: 10.1038/nature04439.
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.
（Mg,Fe）SiO₃的后钙钛矿相被认为是地球最底层地幔（D''层）的主要矿物相。它的性质解释了与该层相关的众多地球物理观测结果，例如D''不连续面、其地形以及该层内的地震各向异性。在此，我们使用一种新颖的模拟技术——第一性原理元动力学，来识别一系列介于钙钛矿相和后钙钛矿相之间的低能量多型堆垛层错结构。元动力学轨迹表明，涉及堆垛层错形成的平面滑动是最有利于相变的途径，并且是钙钛矿和后钙钛矿塑性变形的可能机制。特别是，预测的钙钛矿滑移面为{010}（与实验一致），后钙钛矿的滑移面为{110}（与先前预期的{010}滑移面相反）。主导滑移面决定了织构的晶格优选取向和弹性各向异性。后钙钛矿中的{110}滑移面所需的晶格优选取向程度要小得多，才能解释D''层中剪切波各向异性的地球物理观测结果。
