In Situ Studies of Iron under Pressure: New Windows on the Earth's Core

Experiments on iron with recently developed high-pressure techniques are providing new insights into the nature of the Earth's core. In situ high P-T synchrotron x-ray diffraction studies to above 160 GPa and 3000 K with double-sided, laser-heated diamond-anvil cells demonstrate that the hexagonal closed packed phase (ϵ-Fe) has a wide stability field extending from deep mantle to core conditions. Direct measurements of the melting line of ϵ-Fe to above 100 GPa with these techniques provide constraints on the temperature and density at the inner core boundary. Radial x-ray diffraction measurements carried out at room temperature to 220 GPa have constrained the elasticity, rheology, and acoustic velocities of ϵ-Fe at core pressures. Vibrational properties providing information on thermodynamic and elastic parameters have been measured to above 150 GPa using both synchrotron x-ray and laser Raman spectroscopies. X-ray diffraction studies of liquid iron reveal changes in short-range structure as functions of ...