Microscopic structure of Fe-Ni and Fe-Ni-S molten alloys of geophysical interest

Abstract : The static S(Q) liquid structure factors for binary Fe_xNi_1-x, x=0.90, 0.85, and ternary Fe_0.85Ni_0.05S_0.15 molten alloys are investigated by means of the concurrent use of neutron diffraction and reverse Monte Carlo simulations. The measured G(r) radial distributions reveal atomic orderings varying from that present in the Fe_0.90Ni_0.10 alloy, reminiscent of the ideal bcc structure of solid Fe, to a far more open structure found in Fe_0.85Ni_0.05S_0.15. From data at hand no clear evidence of the clustering of sulfur within the Fe-Ni matrix is found. In contrast, the addition of sulfur leads to significant changes in structural and some dynamical properties that can be inferred from knowledge of the static structure factors. Such dynamical changes seem to arise as a result of a strong decrease of the elastic moduli of the alloys resulting from interactions with a light element rather than from a density effect.