Theoretical predictions of thermodynamic properties, elastic deformation, HCP-FCC structural phase transition and melting of iron at high temperatures up to 18000 K and high pressures up to 4000 GPa

Abstract

In this work, the statistical moment method is extended to determine the thermodynamic properties, elastic deformation, HCP-FCC structural phase transition and melting of iron under extreme conditions. The analytic expressions of structural and thermodynamic quantities (the density, the molar volume, the adiabatic and isothermal compressibilities, the thermal expansion, the heat capacities at constant volume and constant pressure, the Grüneisen parameter), elastic deformation quantities (the Young's modulus, the bulk modulus, the shear modulus, the compressional and shear wave velocities, Gibbs thermodynamic potential), HCP-FCC structural phase transition temperature, and melting temperature are performed capturing the full anharmonicity of lattice thermal vibrations. Theoretical results have been numerically calculated for structural, thermodynamic and elastic deformation quantities of HCP-Fe at high temperatures up to 7000 K and high pressures up to 1400 GPa, HCP-FCC structural phase transition curves and the phase diagram of iron in the range of pressure from 2400 to 4000 GPa. Our results allow a quantitative interpretation of the experimental results, contributing to the prediction of structural features, fundamental properties and geophysical applications of the Earth's core.