Melting and crystal structure of iron at high pressures and temperatures

Abstract

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 ε‐γ‐1 triple point is 60(±5) GPa and 2800(±200) K, based on our data of the ε‐γ phase transition and the observation of melting by in situ x‐ray diffraction. No solid phases other than ε‐Fe and γ‐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.