Melting and crystal structure of iron at high pressures and temperatures

High-pressure melting, phase transitions and structures of iron have been studied to 84 GPa and 3500 K with an improved laser heated diamond anvil cell technique and in situ high P-T x-ray diffraction. At pressures below 60 GPa, the lower bound on the melting curve is close to those measured by Boehler [1993] and Saxena et al. [1993]; however, at pressures above 60 GPa our data indicate melting at higher temperatures than these studies, but still lower than the melting curve of Williams et al [1990]. The epsilon-gamma-1 triple point is 60(+/-5) GPa and 2800(+/-200) K, based on our data of the epsilon-gamma phase transition and the observation of melting by in situ x-ray diffraction. No solid phases other than epsilon-Fe and gamma-Fe were observed in situ at high temperatures (>1000 K) and pressures to 84 GPa. However, the diffraction patterns of temperature quenched products at high pressure can be fit to other structures such as dhcp.