Europhys. Lett., 52 (2), pp. 151–157 (2000) EUROPHYSICS LETTERS 15 October 2000 Structural changes in liquid Fe at high pressures and high temperatures from Synchrotron X-ray Diffraction C. Sanloup 1,3 , F. Guyot 2 , P. Gillet 1 , G. Fiquet 2 , R. J. Hemley 3 , M. Mezouar 4 and I. Martinez 5 1 Laboratoire de Sciences de la Terre, ENSL 46, all´ ee d’Italie, 69364 Lyon cedex 07, France 2 Laboratoire de Min´ eralogie-Cristallographie, IPGP 4, place Jussieu, 75252 Paris cedex 05, France 3 Geophysical Laboratory and Center for High Pressure Research Carnegie Institution of Washington - 5251 Broad Branch Road NW Washington DC 20015, USA 4 ESRF, Experiments Division - B.P. 220, 38043 Grenoble cedex, France 5 Laboratoire des Isotopes Stables, IPGP - Paris, France (received 13 June 2000; accepted 31 August 2000) PACS. 62.50.+p – High-pressure and shock-wave effects in solids and liquids. PACS. 61.10.-i – X-ray diffraction and scattering. PACS. 61.20.-p – Structure of liquids. Abstract. – High-energy synchrotron X-ray diffraction measurements on liquid iron in the vicinity of the δ-γ-liquid triple point (to 2300 K and 5 GPa) reveal significant changes in the structure of the liquid upon increasing pressure and temperature. The second and third neighborshellsinthe g(r)shifttoshorterdistancesanddevelopnewstructurewithincreasing pressure. The results can be interpreted in terms of the liquid acquiring bcc-like local order which evolves to a mixture of bcc- and fcc-like local order as pressure and/or temperature are raised. The properties of iron at high pressure are of great current interest because it is a classic d-electron metal, it exhibits extensive polymorphism at high pressures and temperatures [1–4], and it is the dominant component of planetary cores. Despite this fundamental, technological and geophysical importance, information on the structure of liquid Fe at high pressure has long been prevented because of the low signal levels relative to background and of experimental difficulties arising from the extreme conditions required (above 1810 K, melting temperature of iron at ambient pressure) [5,6]. The advent of third generation synchrotron facilities has opened the prospect for diffraction studies of liquids at high pressure, providing information on possible structural rearrangements induced by pressure and temperature [7,8]. Here we report the first direct study of the structure of liquid iron at high pressures and temperatures using new synchrotron X-ray diffraction methods. Structural changes at high pressure have recently been observed in molten KCl and KBr at temperatures above the subsolidus B1-B2 transition, with the 2nd neighbor ion distance c  EDP Sciences