The structure of amorphous iron at high pressures to 67 GPa measured in a diamond anvil cell

We report the results of room temperature compression studies of amorphous iron up to 67 GPa. The experiments were performed with a modified diamond anvil cell (DAC) that allows for measurements of X-ray scattering to a maximum momentum of 86.6 nm^-1 using a monochromatic beam at a wavelength of 0.3311 Å. It is shown that accurate structural determination can be made for amorphous materials in a DAC to ultra high pressures. The dense random-packing model is favored to interpret our observations for amorphous iron. The resultant structure factor and the pair distribution function show that the dominant peak does not significantly change in shape and in intensity with the increase of pressure, except for peak positions. This observation is consistent with essentially zero pressure dependence of the coordination number and ratios of distances derived from the obtained pair distribution functions at high pressures. It is thus proposed that the structural contraction with the increase of pressure for amorphous iron is isotropic, which allows us to estimate volume changes as a function of pressure from the positions of the first peak in the pair distribution function. The compression behavior is found to be similar to those of b.c.c.-Fe and h.c.p.-Fe.