Phase diagrams of Fe–Si alloys at 3–5 GPa from electrical resistivity measurements

Abstract

One of the most extensively investigated properties of Fe is electrical resistivity (ρ) which features several well-established temperature (T) dependent characteristics. Based on systematic data for Fe and Fe–Si alloys and guidance from the 1 atm diagram, the T-X (composition X) phase diagram can be obtained at constant pressure (P) by plotting maps of constant ρ contours, proposed herein to be called ‘iso-ohms’, maps of constant δρ/δT, as well as maps of variations of exponent x in power law fits to ρ(T^x). Electrical resistivity measurements of Fe-(≤ 17wt%)Si alloys are available at 3–5 GPa and up to liquid temperatures. This study provides a new approach to mapping high P–T structural phase diagrams in the Fe-rich region of the Fe–Si system at moderate pressures and may be used for other compositions. Maps of iso-ohms suggest the α phase is the less resistive phase followed by α₂, α₁, η + α₁, and ε + α₁. Above ~ 11 wt% Si, the ε + α₁ displays a higher ρ than the liquid phase. This is discussed in terms of s and d electron scattering. Maps of constant δρ/δT emphasize the magnetic transition and boundary between the ε + α₁ and η + α₁ phases, while variations of exponent x outline the α₂ region. The Fe–Si system is of interest to the cores of the moon and Mercury.