Portal de Periódicos da CAPES

Stability and equation of state of CaSiO 3 ‐Perovskite to 134 GPa

1989; American Geophysical Union; Volume: 94; Issue: B12 Linguagem: Inglês

10.1029/jb094ib12p17889

2156-2202

H. K. Mao, L. C. Chen, Russell J. Hemley, A. P. Jephcoat, Yan Wu, William A. Bassett,

Crystal Structures and Properties

The stability and P ‐ V equation of state of CaSiO 3 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 CaSiO 3 ‐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 CaSiO 3 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 V 0 = 45.37±(0.08) Å 3 , density ρ 0 = 4.252(±0.008) Mg/m 3 , and bulk modulus K 0 = 281(±4) GPa, with an assumed bulk modulus pressure K 0 ′ = 4. These parameters are close to those of (Mg 0.88 Fe 0.12 )SiO 3 ‐perovskite and to those inferred by the Preliminary Reference Earth Model for the lower mantle. Hence, CaSiO 3 must be considered an invisible component, in terms of density and bulk modulus constraints, in the lower mantle. Mantle composition models with both high and low calcium content can satisfy existing seismological constraints for the lower mantle.