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

The structure and equation of state for CaIrO 3 -type MgSiO 3 were determined using high-pressure powder X-ray diffraction from 116 to 144 Gpa. The CaIrO 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 ’ and V 0 were set to 4 and 162.86 Å 3 , respectively. This indicates that the bulk modulus of MgSiO 3 decreases when the phase transition occurs, because the bulk modulus of perovskite-type MgSiO 3 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.