The α-γ-ε triple point of iron investigated by high pressure-high temperature neutron scattering

We present high pressure-high temperature diffraction data in the 0-10 GPa and 300-1000 K range of all three main iron phases. The refinements of the diffraction patterns give molar volumes to high precision and show that the alpha-gamma-epsilon triple point is located at 8.2 +/- 0.1 GPa and 678 K. These values are significantly lower than currently admitted (10.4 GPa/740 K), but are consistent with reported in situ x-ray diffraction data obtained in multianvil presses. These measurements have been made possible by the use of a high P/T cell which uses metallic toroidal gaskets and which suffers from less absorption, gives clean diffraction patterns, and shows better pressure performance than other setups. (c) 2008 American Institute of Physics.