The compressibility of a natural composition calcium ferrite-type aluminous phase to 70 GPa

In situ X-ray diffraction (XRD) experiments of a calcium ferrite-type aluminous phase that is a sodium host mineral of subducted oceanic crusts into the Earth’s lower mantle have been carried out using a laser-heated diamond anvil cell (LHDAC), up to a pressure of 70 GPa with synchrotron radiation source at the Photon Factory (PF) in Japan. The sample was heated using a Nd:YAG laser at each pressure increment to relax the deviatoric stress in the sample. XRD measurements were carried out at 300 K using an angle-dispersive technique. The pressure was determined from an internal platinum pressure calibrant. A Birch–Murnaghan equation of state (EOS) was determined from the experimental unit cell parameters: volume V0=244.07 (±55) Å3, density ρ0=4.143 g/cm3, bulk modulus K0=253 (±14) GPa, and K0′=3.6 (±0.6). When the first pressure derivative of the bulk modulus K0′ was fixed at 4, the value of K0=243 (±2) GPa was obtained. The density of the calcium ferrite-type aluminous phase is lower than those of co-existing Mg-, Ca-perovskite, and hexagonal aluminous phase in subducted oceanic crusts.