Equation of State, Phase Stability of (Mg0.92, Fe0.08)SiO3 Perovskite from Shock Wave Study and Its Geophysical Implications

Abstract

13 shots of shock compression data were measured for enstatite (Mg0.92, Fe0.08)SiO3 with initial density of 3.06g/cm3 up to 140 GPa, using impedance‐match method and electrical probe technique. The relationship between shock wave velocity D and particle velocity u can been described linearly by: D = 3.76 +1.48u(km/s), and no evidence of phase transition was shown in the experimental shock pressure range. Our experimental Hugoniot is about 7% denser than the model Hugoniot of (Mg0.92, Fe0.08)O (Mw.) plus SiO2(St.) calculated by additive principle. This excluded the possibility that chemical decomposition of enstatite with perovskite structure to oxides would happen during shock compression up to 140GPa. The Grüneisen parameter γobtained by fitted our experimental data to: γ=γ0 (ρ0/ρ)q, yields γ0=1.84, q=1.69, with ρ0=4.19g/cm3. By using the third‐order Birch‐Murnaghan finite strain equation of state (EOS), Our shock experimental data yield a zero‐pressure bulk modulus K0s=260.09GPa and pressure derivative K0s =4.17, given our new value of γ, with ρ0=4.19g/cm3. From density constraint only, the purely perovskite model of (Mg1−x, Fex)SiO3 (x=0∼0.1) can explain that of PREM well.