MELTING AND CRYSTAL-STRUCTURE OF IRON AT HIGH-PRESSURES AND TEMPERATURES

High-pressure melting, phase transitions and structures of iron have b een 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 press ures below 60 GPa, the lower bound on the melting curve is close to th ose measured by Boehler [1993] and Saxena et al. [1993]; however, at p ressures above 60 GPa our data indicate melting at higher temperatures than these studies, but still lower than the melting curve of William s et al [1990]. The epsilon-gamma-1 triple point is 60(+/-5) GPa and 2 800(+/-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 hi gh temperatures (>1000 K) and pressures to 84 GPa. However, the diffra ction patterns of temperature quenched products at high pressure can b e fit to other structures such as dhcp.