The effects of one-dimensional hydrogen on the ferroelastic transition and elasticity of stishovite are determined up to 52.5 GPa using x-ray diffraction, Raman spectroscopy, and first-principles calculations. In contrast to the well-studied hydrogen-free stishovite or that with hydrogarnetlike point defects, stishovite with hydrogen intercalation develops into the ${\mathrm{CaCl}}_2$-type phase at a remarkably low pressure of 3.3 GPa, but the shear instability is postponed to 17.3 GPa. We rationalize the decoupling of the ferroelastic transition by modeling the spontaneous strains using Landau theory, and reveal a two-stage hierarchical progression of lattice distortion. Strains are originated from ${\mathrm{SiO}}_6$ octahedra surrounding the channel-like hydrogen defects, then subsequently propagate to bulk lattice with increasing pressure. Despite being the lightest atom and x-ray invisible, the elastic properties of stishovite are highly sensitive to the hydrous defect. Hydrogen-bearing stishovite may therefore induce shear anomalies in hydrous slabs at much shallower mantle depths than previously thought.

Close

PrevNext

View figure in article

• Distortions & defects
• Earth's interior
• High-pressure studies
• Line defects
• Phase transitions
• Crystal structures
• Single crystal materials
• First-principles calculations
• Pressure techniques
• Raman spectroscopy
• X-ray diffraction