Equation of state of CaIrO3-type MgSiO3 up to 144 GPa

摘要

The structure and equation of state for CaIrO₃-type MgSiO₃ were determined using high-pressure powder X-ray diffraction from 116 to 144 GPa. The CaIrO₃-type phase remained stable over this entire pressure range. At each pressure increment, the sample was heated with a laser to relax the deviatoric stress in the sample. Pressure-volume data could be fitted to the Birch-Murnaghan equation of state with K₀ = 237(1) GPa using Anderson’s gold pressure standard, when K₀’ and V₀ were set to 4 and 162.86 Å3, respectively. This indicates that the bulk modulus of MgSiO₃ decreases when the phase transition occurs, because the bulk modulus of perovskite-type MgSiO₃ is 250–260 GPa. The b axis of the unit-cell parameter was more compressive than the a and c axes. The unit-cell volumes at high pressures, observed in high-pressure experiments, were slightly smaller than those predicted by theoretical studies.