Lattice preferred orientation in CaIrO₃ perovskite and post-perovskite formed by plastic deformation under pressure

Lattice preferred orientations (LPO) developed in perovskite and post-perovskite structured CaIrO₃ were studied using the radial X-ray diffraction technique combined with a diamond anvil cell. Starting materials of each phase were deformed from 0.1 MPa to 6 GPa at room temperature. Only weak LPO was formed in the perovskite phase, whereas strong LPO was formed in the post-perovskite phase with an alignment of the (010) plane perpendicular to the compression axis. The present result suggests that the (010) is a dominant slip plane in the post-perovskite phase and it is in good agreement with the crystallographic prediction, dislocation observations via transmission electron microscopy, and a recent result of simple shear deformation experiment at 1 GPa-1,173 K. However, the present result contrasts markedly from the results on MgGeO₃ and (Mg,Fe)SiO₃, which suggested that the (100) or (110) is a dominant slip plane with respect to the post-perovskite structure. Therefore it is difficult to discuss the behavior of the post-perovskite phase in the Earth's deep interior based on existing data of MgGeO₃, (Mg,Fe)SiO₃ and CaIrO₃. The possible sources of the differences between MgGeO₃, (Mg,Fe)SiO₃ and CaIrO₃ are discussed.