Resistivity saturation of hcp Fe-Si alloys in an internally heated diamond anvil cell: A key to assessing the Earth's core conductivity

Abstract

Electrical resistivity and thermal conductivity of iron (Fe)-light element alloys at high pressure and temperature are key parameters to constrain the dynamics and thermal evolution of the Earth's core. We determined the electrical resistivity of hcp Fe-2, 4 and 6.5 wt.% silicon (Si) alloys up to 117 GPa and 3120 K using a four-terminal method in an internally heated diamond-anvil cell. The temperature dependence of electrical resistivity of hcp Fe-Si alloys was suppressed as both Si concentration and temperature increased, which indicates the resistivity saturation phenomenon: the electrical resistivity of metal asymptotically approaches the “saturation resistivity”. Our results are fully reproduced by a highly resistive saturation model, and the obtained saturation resistivities for hcp Fe-Si alloys are comparable to those for hcp pure Fe at around 100 GPa. If Si is a major light element in the Earth's core, the pure Fe like saturation resistivity would keep the core conductivity high enough to induce active dynamics there and rapid growth of the inner core.