Stability and equation of state of CaSiO₃-perovskite to 134 GPa

The stability and P-V equation of state of CaSiO₃ have been investigated using in situ diamond-anvil X-ray diffraction techniques to 134 GPa, a pressure equivalent to that at the core-mantle boundary. Samples were heated by YAG laser at each pressure increment at high pressures to accelerate phase transitions. X-ray diffraction measurements were carried out at 300 K using both energy-dispersive synchrotron and sealed-tube film techniques. Quenched CaSiO₃-perovskite was observed to remain metastable close to 0.1 MPa, and to convert rapidly to an amorphous phase on pressure release. The simple cubic perovskite phase of CaSiO₃ was found to be the stable phase for all lower mantle pressure conditions. All 47 P-V data points were used to obtain a third-order Birch-Murnaghan equation of state with zero-pressure parameters: unit cell volume V₀ = 45.37 ± (0.08) ų, density ρ₀ = 4.252(±0.008) Mg/m³, and bulk modulus K₀ = 281(±4) GPa, with an assumed bulk modulus pressure K₀′ = 4. -from Authors