P-V-T equation of state of epsilon iron and its densities at core conditions

TL;DR

This paper introduces a new p-V-T equation of state for epsilon iron, tested against experimental data, showing comparable or better accuracy than existing models, and used to estimate inner core densities.

Contribution

A novel p-V-T equation of state for epsilon iron is developed and validated, providing improved or comparable fits to experimental data and implications for Earth's inner core composition.

Findings

New EoS achieves RMSD of 0.021 cm3 in molar volume

Calculated inner core densities are lower than current estimates

New parameters suggest possible light elements in the core

Abstract

The author's new p-V-T Equation of State is tested against the available experiments of epsilon iron. The root-mean-square-deviations (RMSD) of the molar volume, pressure, and temperature are 0.021 cm3, 2.0 GPa and 144.9 K respectively. Separating the experiments into 200 K ranges the new EoS was compared to the most widely used finite strain, interatomic potential, and empirical isothermal EoSs such as the Burch-Murnaghan, the Vinet, and the Roy-Roy respectively. Correlation coefficients, RMSDs of the residuals and Akaike Information Criteria were used for evaluating the fittings. Based on these fitting parameters the new p-V-T EoS is equal or better than the conventional isothermal EoSs. The newly defined parameters were used to calculate the density of the inner core. The calculated densities are significantly lower than the current consensus indicating that it might be too early excluding the possibility of a pure iron-nickel core with no light elements.