Relationship between structural variation and spin transition of iron under high pressures and high temperatures

• X-ray diffraction patters of iron were measured by the synchrotron experiments.
• High-pressure experiments were performed by a laser-heated diamond anvil cell.
• An abnormal change in cell parameter ratio of hcp-Fe was confirmed.
• Structural change indicates the spin transition of iron at high temperatures.

The high-pressure and high-temperature behavior of the spin state in hexagonal close-packed (hcp) Fe has been examined using synchrotron X-ray diffraction up to 180 GPa pressure and 2000 K temperature using the diamond anvil cell technique. The spin transition of the high-pressure Fe phase with the hcp structure from high to low state was confirmed. A significant change in the c/a ratio of the cell parameters of hcp-Fe was observed at the transition boundary. The spin transition pressure, P, increased as the temperature increased. The transition boundary was estimated to be P (GPa)=51+0.045×T (K).