Electrical resistivity of hcp Fe-Si alloy at high pressure and temperature

Silicon (Si) has been repeatedly suggested to be major light element in the Earth's core that mainly consists of iron. About 6 wt.%Si is thought to be incorporated into the Earth's core (Hirose et al., 2013). Alloying the light element(s) affects a variety of physical properties of iron. Electrical and thermal conductivities strongly constrain the dynamics and thermal evolution of Earth's core and these parameters are connected by Wiedemann-Franz law(κ= σLT; κ: thermal conductivity, σ: electrical conductivity, L: Lorenz number, T: absolute temperature). However, measurements of electrical and thermal conductivities under static condition at extremely high pressures (P) and temperature (T) are limited for pure iron (Ohta et al., 2016; Konôpková et al., 2016). The estimates of the core conductivity considering the effect of light element(s) have been done based on the resistivity saturation model, but the validity of the model at the core condition is unclear (Gomi et al., 2013; 2016).

In this study, we examined electrical resistivity (the reciprocal of electrical conductivity) of Fe-4 wt.%Si at high P-T conditions in an internally-heated diamond anvil cell. Our results of the electrical resistivity of Fe-4 wt.%Si at 45 GPa up to 1520 K showed its nonlinear temperature dependence, indicating the occurrence of the resistivity saturation. The resistivity saturation in Fe-Si alloy observed in this study supports the notion of high core conductivity and resulting molten lowermost mantle and young inner core.

Hirose et al. (2013)Annu Rev Earth Pl Sc 41, 657-691; Ohta et al. (2016) Nature 534, 95-98; Konôpková et al. (2016) Nature 534, 99-101; Gomi et al. (2013) Phys Earth Planet In 224, 88-103; Gomi et al. (2016) Earth Planet. Sci. Lett. 451, 51-61.