Saturation of electrical resistivity of solid iron at Earth's core conditions.

Monica Pozzo,Dario Alfè

doi:10.1186/s40064-016-1829-x

Abstract

We report on the temperature dependence of the electrical resistivity of solid iron at high pressure, up to and including conditions likely to be found at the centre of the Earth. We have extended some of the calculations of the resistivities of pure solid iron we recently performed at Earth’s core conditions (Pozzo et al. in Earth Planet Sci Lett 393:159–164, 2014) to lower temperature. We show that at low temperature the resistivity increases linearly with temperature, and saturates at high temperature. This saturation effect is well known as the Mott-Ioffe-Regel limit in metals, but has been largely ignored to estimate the resistivity of iron at Earth’s core conditions. Recent experiments (Gomi et al. in Phys Earth Planet Int 224:88–103, 2013) coupled new high pressure data and saturation to predict the resitivity of iron and iron alloys at Earth’s core conditions, and reported values up to three times lower than previous estimates, confirming recent first principles calculations (de Koker et al. in Proc Natl Acad Sci 109:4070–4073, 2012; Pozzo et al. in Nature 485:355–358, 2012, Phys Rev B 87:014110-10, 2013, Earth Planet Sci Lett 393:159–164, 2014; Davies et al. in Nat Geosci 8:678–685, 2015). The present results support the saturation effect idea.

Highlights

The thermal and electrical conductivities of iron at Earth’s core conditions (pressures between 135 and 364 GPa and temperatures between 4000 and 6000 K) are the two key parameters needed to determine the fundamental time scales for diffusion of heat and magnetic field in the core of our planet
The thermal and electrical conductivities of iron at Earth’s core conditions are the two key parameters needed to determine the fundamental time scales for diffusion of heat and magnetic field in the core of our planet
The main reason for the much higher conductivities suggested by the recent experiments of Gomi et al (2013), later confirmed by direct measurements by Ohta et al (2014, 2015), was the inclusion of saturation effects in the extrapolation of the conductivities at high temperature

Summary

Introduction

The thermal and electrical conductivities of iron at Earth’s core conditions (pressures between 135 and 364 GPa and temperatures between 4000 and 6000 K) are the two key parameters needed to determine the fundamental time scales for diffusion of heat and magnetic field in the core of our planet. Recent theoretical calculations predicted resistivities of iron and iron alloys at Earth’s core conditions (de Koker et al 2012; Pozzo et al 2012, 2013, 2014; Davies et al 2015) that were later found to be very close to those estimated by Gomi et al (2013), supporting the idea of high temperature saturation.

Results

Conclusion