Microscopic structural change in a liquid Fe-C alloy of similar to 5GPa

The structure of a liquid Fe-3.5wt% C alloy is examined for up to 7.2GPa via multiangle energy-dispersive X-ray diffraction using a Paris-Edinburgh type large-volume press. X-ray diffraction data show clear changes in the pressure-dependent peak positions of structure factor and reduced pair distribution function at 5GPa. These results suggest that the liquid Fe-3.5wt% C alloys change structurally at approximately 5GPa. This finding serves as a microscopic explanation for the alloy's previously observed density change at the same pressure. The pressure dependencies of the nearest and second neighbor distances of the liquid Fe-3.5wt% C alloy are similar to those of liquid Fe which exhibits a structural change near the bcc-fcc-liquid triple point (5.2GPa and 1991K). Similarities between Fe-3.5wt% C and Fe suggest that a density change also occurs in liquid Fe and that this structural change extends to other Fe-light element alloys.