Radial x-ray diffraction experiments were conducted under nonhydrostatic compression on [Formula presented] to 60 GPa in a diamond anvil cell. This ratio of differential stress to shear modulus [Formula presented] is 0.019(3)–0.037(5) at [Formula presented]. The ratio for octahedrally coordinated stishovite is lower by a factor of about 2 than observed in four-coordinated silicates. Using a theoretical model for the shear modulus, the differential stress of stishovite is found to be 4.5(1.5) GPa below 40 GPa and to decrease sharply as the stishovite–[Formula presented]-type phase transition boundary is approached. Inversion of measured lattice strains provides direct experimental evidence for softening of [Formula presented].
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)