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 CaIr-O-3-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 K-0 = 237(1) GPa using Anderson's gold pressure standard, when K-0(1) and V-0 were set to 4 and 162.86 angstrom(3), 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.