P-V-T equation of state for ε-iron up to 80 GPa and 1900 K using the Kawai-type high pressure apparatus equipped with sintered diamond anvils

In order to determine the P‐V‐T equation of state of ε‐iron, in situ X‐ray observations were carried out at pressures up to 80 GPa and temperatures up to 1900 K using the Kawai‐type high pressure apparatus equipped with sintered diamond anvils which was interfaced with synchrotron radiation. The present results indicate the unit cell volume at ambient conditionsV0 = 22.15(5) Å3, the isothermal bulk modulus KT0 = 202(7) GPa and its pressure derivative K′T0 = 4.5(2), the Debye temperature θ0 = 1173(62) K, Grüneisen parameter at ambient pressure γ0 = 3.2(2), and its logarithmic volume dependence q = 0.8(3). Furthermore, thermal expansion coefficient at ambient pressure was determined to be α0(K−1) = 3.7(2) × 10−5 + 7.2(6) × 10−8(T‐300) and Anderson‐Grüneisen parameterδT = 6.2(3). Using these parameters, we have estimated the density of ε‐iron at the inner core conditions to be ∼3% denser than the value inferred from seismological observation. This result indicates that certain amount of light elements should be contained in the inner core as well as in the outer core but in definitely smaller amount. Key Points Precise determination of volume at high temperature under pressure Newly developed pressure generation technique enable us to do this research Density deficit of inner core of ~3% is largely smaller than that of outer core