PHASE-DIAGRAM OF IRON BY IN-SITU X-RAY-DIFFRACTION - IMPLICATIONS FOR EARTH CORE

The phase diagram of iron has been studied to 130 gigapascals (1 gigapascal = 10(4) atmospheres) and 3500 kelvin by a combined laser-heated diamond-anvil cell and x-ray diffraction technique that provides direct identification of the solid phases. Iron in the hexagonal close-packed (hcp) phase (epsilon-Fe) is stable from 50 to at least 110 gigapascals at high temperatures. The wide stability field of epsilon-Fe indicates that this polymorph should currently be considered the most relevant solid phase for Earth's core. The triple point between the gamma, epsilon, and liquid phases is located at 2500 +/- 200 kelvin and 50 +/- 10 gigapascals, There is evidence for a phase with a double hcp structure below 40 gigapascals and for another transition above 110 gigapascals and 3000 kelvin.