A laser-heated diamond-anvil cell that is capable of operating up to a pressure of 63 GPa, with X-ray diffraction facilities using a synchrotron radiation source at the SPring-8, has been developed to observe the compressibility of a hexagonal aluminous phase, Si1.98] ∑9.27O12. The hexagonal aluminous phase is a potassium host mineral from the subducted oceanic crust in the Earth's lower mantle. A sample was heated using a YAG laser at each pressure increment to relax the deviatoric stress in the sample. X-ray diffraction measurements were carried out at 300 K using an angle-dispersive technique. Pressure was measured using an internal platinum pressure calibrant. The observed unit-cell volumes were used to obtain a third-order Birch-Murnaghan equation of state: unit-cell volume Vo = 185.94(±16) Å3, density ρo = 4.145 g/cm3, and bulk modulus Ko = 198(±3) GPa when the first pressure is derivative of the bulk modulus K′0 is fixed to 4. The density of hexagonal aluminous phase is lower than that of coexisting Mg-perovskite in the subducted oceanic crust.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Geochemistry and Petrology