Electrical conductivity of warm dense silica from double-shock experiments

M Guarguaglini,F Soubiran,R Bolis,T Vinci,A Ravasio,E Brambrink,A Benuzzi-Mounaix,J.-A Hernandez

doi:10.1038/s41467-021-21046-1

Abstract

Understanding materials behaviour under extreme thermodynamic conditions is fundamental in many branches of science, including High-Energy-Density physics, fusion research, material and planetary science. Silica (SiO2) is of primary importance as a key component of rocky planets’ mantles. Dynamic compression is the most promising approach to explore molten silicates under extreme conditions. Although most experimental studies are restricted to the Hugoniot curve, a wider range of conditions must be reached to distill temperature and pressure effects. Here we present direct measurements of equation of state and two-colour reflectivity of double-shocked α-quartz on a large ensemble of thermodynamic conditions, which were until now unexplored. Combining experimental reflectivity data with numerical simulations we determine the electrical conductivity. The latter is almost constant with pressure while highly dependent on temperature, which is consistent with simulations results. Based on our findings, we conclude that dynamo processes are likely in Super-Earths’ mantles.

Highlights

Understanding materials behaviour under extreme thermodynamic conditions is fundamental in many branches of science, including High-Energy-Density physics, fusion research, material and planetary science
For SiO210 and more complex silicates[11], experimental results obtained along the principal Hugoniot exhibit changes in optical properties compatible with the semi-conducting to semi-metallic transition predicted by ab initio calculations
A VISARindependent time-resolved reflectivity measurement at 532 nm was implemented in the setup to corroborate the reflectivity measurements obtained from the Velocity Interferometer Systems for Any Reflector (VISAR) fringe system

Summary

Introduction

Understanding materials behaviour under extreme thermodynamic conditions is fundamental in many branches of science, including High-Energy-Density physics, fusion research, material and planetary science. Recent ab initio calculations[7,8] suggested that, under pressures and temperatures typical of hot young super-Earths’ interiors, the electrical conductivity of molten silica is high enough (~100 Ω−1cm−1) to generate a magnetic field from a self-sustaining dynamo. Further theoretical investigations have predicted that warm dense SiO2 electrical conductivity does not evolve monotonically as a function of the pressure in the megabar regime[9], which is possibly related to coordination changes[7,9]. Experimental validations of these numerical predictions can be obtained using shock compression, where multimegabar pressures and several thousand Kelvin temperatures can be routinely achieved. We confirm that a dynamo process is very possible in a long-lived SiO2-rich magma ocean

Methods

Results

Conclusion