High resolution three-dimensional X-ray diffraction study of dislocations in grains of MgGeO3 post-perovskite at 90 GPa

MgGeO3 post-perovskite (pPv) is a lower pressure analogue of MgSiO3-pPv, which is believed to be the main constituent of the Earth's D ''. layer. Understanding the physical properties of this phase is critical to explain seismological observations as seismic anisotropy is likely linked to lattice preferred orientation in post-perovskite, which is governed by the motion of defects such as dislocations. Here, we apply in-situ three-dimensional X-ray diffraction to a polycrystalline sample of MgGeO3-pPv at 90 GPa. We demonstrate how the method can be used to follow individual grains within the material, including their individual orientations, positions, and strain tensors. We then use X-ray line profile analysis to characterize dislocations in the grains. The most probable slip systems are 1/2 < 110 > gliding on {(1) over bar 10} or (001) and [110](001), with a smaller contribution of [100](001) and [001] dislocations. These slip systems are shown to be consistent with observations of seismic anisotropy in D ''.