THE ORTHORHOMBIC STRUCTURE OF IRON - AN IN-SITU STUDY AT HIGH-TEMPERATURE AND HIGH-PRESSURE

An in situ angle-dispersive x-ray diffraction study was undertaken of iron in a laser-heated, diamond-anvil cell up to 2375 kelvin and betwe en 30 and 100 gigapascals in Al2O3-and SiO2-pressure media. The resolu tion and reliability of diffraction peak intensities allow quantitativ e assessment of a structural model. The results confirm that iron unde rgoes a phase transformation at high pressures and temperatures. The s pace group is Pbcm for an orthorhombic lattice, and the atomic topolog y is close to that of epsilon hexagonal close-packed iron.