In situ X-ray diffraction studies of iron to Earth-core conditions

The high-pressure, high-temperature behavior of iron has been investigated to 161 GPa and 3000 K by in situ synchrotron X-ray diffraction with double-side laser-heated diamond anvil cells. We found that only alpha-, gamma- and epsilon-Fe can be clearly verified as the stable solid phase in the P-T range studied. Only epsilon-Fe is observed from deep lower mantle (similar to 1500 km) to outer core conditions. Within the P-T range examined, we did not observe a significant change with pressure or temperature on the c/a ratio of epsilon-Fe. The melting curve of iron has been determined to 105 GPa. A Lindeman law fit gives a melting point of iron at the inner core boundary of 5800 (+/-200) K, which provides an upper bound on the temperature at that depth. We also examine numerous experimental factors that may complicate the analysis of high P-T diffraction data, and discuss the effects of sample stress on the X-ray diffraction results. (C) 2004 Elsevier B.V. All rights reserved.