Thermal equation of state of Al- and Fe-bearing phase D

Pressure-volume-temperature relations have been measured to 20.6 GPa and 1273 K for Fe- and Al-bearing phase D (Mg_0.99Fe_0.12 Al_0.09Si_1.75H_2.51O₆) using synchrotron X-ray diffraction with SPEED-MkII multianvil press at SPring-8 facility. The analysis of room temperature data fitted to a third-order Birch-Murnaghan equation of state (EOS) yields V₀ = 85.32 ± 0.02 ų; K₀ = 141.5 ± 3 GPa and K' = 6.2 ± 0.4. The pressure was calibrated using the Au EOS by Anderson et al. (1989). Fixing K'to, 4.0, gives K₀ = 155.3 ± 0.8 GPa. These values are consistent with thermal EOS analysis as well as previous estimations for Fe-Al-bearing and Fe-Al-free phase D. A fit to high-temperature P-V-T data using Birch-Murnaghan EOS yields V₀ = 85.32 ± 0.02 ų ; K₀ = 139.6 ± 3.0 GPa; K'= 6.6 ± 0.4; (∂K_T/∂T)p= - 0.023 (8) GPa K^-1 and zero-pressure thermal expansion α = a₀ + a₁ T with a₀ = 3.4 (2) × 10^-5 K^-1 and a₁ = 0.4 (6) × 10^-8 K^-1. The estimated Anderson-Grüneisen parameter is δT = 4.9. Lattice dynamical approach using the Mie-Grüneisen-Debye EOS yields Grüneisen parameter γ₀ = 1.09 ± 0.09 and q = 0.42 ± 0.97, if Debye temperature χ₀ fixed at 920 K, as calculated from sound velocities. The EOS from this study enables the accurate estimation of the density of phase D in a pyrolitic composition under deep mantle conditions. The density reduction of hydrated subducting, slab (∼1 wt.% H₂O) in the lower mantle due to the presence of ∼7% of phase D would be 1.0%.