Slip Systems in MgSiO ₃ Post-Perovskite: Implications for D ′′ Anisotropy

Abstract

Understanding deformation of mineral phases in the lowermost mantle is important for interpreting seismic anisotropy in Earth's interior. Recently, there has been considerable controversy regarding deformation-induced slip in MgSiO(3) post-perovskite. Here, we observe that (001) lattice planes are oriented at high angles to the compression direction immediately after transformation and before deformation. Upon compression from 148 gigapascals (GPa) to 185 GPa, this preferred orientation more than doubles in strength, implying slip on (001) lattice planes. This contrasts with a previous experiment that recorded preferred orientation likely generated during the phase transformation rather than deformation. If we use our results to model deformation and anisotropy development in the D'' region of the lower mantle, shear-wave splitting (characterized by fast horizontally polarized shear waves) is consistent with seismic observations.

High-pressure studies with x-rays using diamond anvil cells

“…When properly quantified, experiments under deviatoric stress can provide rich additional information about strength, plasticity and rheology of the samples that are unavailable with hydrostatic experiments [87]. The uniaxial compression of a DAC is suitable for quantitative studies of deviatoric stress at ultrahigh pressures [88][89][90].…”

“…With the orientation distribution information, we can calculate polycrystal physical properties based on our knowledge of single-crystal physical properties (e.g., see a review article [558] and references therein). Pole figure analysis also provides important information in understanding the mechanisms of texture, such as the dislocation glide during deformation [89,[559][560][561], dislocation mechanism of nanomaterials [308,493], recrystallization (e.g., [562]), grain boundary effect (e.g., [563]), and inherited textures through phase transformations (e.g., [564]). …”

“…The relative intensity at different angles reveals the preferred orientation of a polycrystalline sample. The inverse pole figure from such data can be used to determine sample deformation and slip mechanism (e.g., [89]). …”

Detecting grain rotation at the nanoscale

“…In material science and engineering, texture control is essential in improving the strength and lifetime of structural materials (1). In Earth science, understanding texture development of minerals is important for interpreting seismic anisotropy in the Earth's interior (2)(3)(4)(5).…”

X-Ray Diffraction under Extreme Conditions at the Advanced Light Source

“…This involved redirecting the double-sided Infrared (IR) laser beam and pyrometry optics by 90 degrees in the horizontal plane. Although measuring texture and material strength has originally been developed by the Earth Science community to elucidate the plastic behavior of the Earth's interior (e.g., Gleason and Mao [32], Miyagi et al [33], Miyagi et al [34], Miyagi and Wenk [35], Wenk et al [36]), this technique has also been applied to shed light on the strength of ultra-hard and/or nano-sized material (e.g., Chen et al [37], Xie et al [38], Xie et al [39]). One of the more challenging aspects of in-situ laser heating (axial or radial geometry) is the extraction of a reliable temperature during the heating experiment.…”