Viscosity of Earth's inner core constrained by Fe-Ni interdiffusion in Fe-Si alloy in an internal-resistive-heated diamond anvil cell

Diffusivity in iron (Fe) alloys at high pressures and temperatures imposes constraints on the transport properties of the inner core, such as viscosity. Because silicon (Si) is among the most likely candidates for light elements in the inner core, the presence of Si must be considered when studying difusivity in the Earth's inner core. In this study, we conducted diffusion experiments under pressures up to about 50 GPa using an internal-resistive-heated diamond-anvil cell (DAC) that ensures stable and homogeneous heating compared with a conventional laser-heated DAC and thus allows us to conduct more reliable difusion experiments under high pressure. We determined the coeficients of Fe-nickel (Ni) interdiffusion in the Fe-Si 2 wt% alloy. The obtained difusion coeficients follow a homologous temperature relationship derived from previous studies without considering Si. This indicates that the efect of Si on Fe-Ni interdifusion is not significant. The upper limit of the viscosity of the inner core inferred from our results is low, indicating that the Lorentz force is a plausible mechanism to deform the inner core.