Structure of b-iron at High Temperature and Pressure

D. Andrault et al. (1) conducted an in situ x-ray study of heated iron at high pressure (P) and found a structural transformation of « (hexagonal close packed, hcp) iron to another phase, which they assign to an orthorhombic lattice. There are two problems with this con-clusion. First, their method, applying struc-tural refinement for the purpose of “quantita-tive assessment of a structural model, ” is invalid. Second, we question whether phase analysis of collected x-ray patterns can be interpreted as a mixture of known iron phases [ « (hcp), or b (dhcp, double hexagonal close packed), or both], iron oxide, and pressure medium