Mass Transport and Structural Properties of Binary Liquid Iron Alloys at High Pressure

Abstract

AbstractWe determine mass transport and structural properties of binary liquid iron alloys over a wide density (5.055–11.735 g·cm−3) and temperature range (2,500–6,500 K) using first‐principles molecular dynamics. Compositions consist of 96 at% Fe and 4 at% ϕ, where ϕ = H, C, N, O, Mg, Si, S, or Ni. Self‐diffusion coefficients (D) of Fe and ϕ range from 3.5·10−9 to 1.9·10−7 m2·s−1. Results show a relation between mean atomic radius and diffusivity ratio for the alloying element and iron: Si and Ni are “iron‐like” with similar atomic radii and D compared with those of Fe; H, C, N, O, and S are “small non‐iron‐like” with smaller atomic radii and larger D; and Mg transitions from “large non‐iron‐like” with a larger atomic radius and smaller D at low density to iron‐like under conditions of the Earth's core. The effect of pressure on D for C, N, and O is negligible for densities below ~8 g·cm−3, accompanied by an increase in average coordination numbers to ~6, and an increase in mean atomic radii. For densities above ~8 g·cm−3, diffusivities and atomic radii of these elements decrease monotonically with pressure, which is typical for the iron‐like alloying elements as well as for H, Mg, and S over the whole compression range. While atomic radius ratios move toward unity with compression, diffusivity ratios for the alloying element relative to iron tend to increase for the “non‐iron‐like” elements with density.