Melting, density, and anisotropy of iron at core conditions: new x-ray measurements to 150 GPa

Abstract

Melting temperatures of iron up to 130 GPa and compressibility to 150 GPa were measured by X-ray diffraction in the double-sided laser-heated diamond cell. New experimental features are the very tightly focused X-ray beam, in situ alignment of X-ray beam and hot spot, and rapid data acquisition. The melting temperatures are in good agreement with previous optical measurements supporting 'low' melting temperatures in the core. Above 70 GPa only the (hcp)-Fe phase is found. The measured densities of the annealed iron samples yield an accurate equation of state. The c/a ratio of iron decreases with pressure but shows an increase with temperature and at core conditions is nearly the same as at low pressure.