Work

Equation of State Parameters of hcp-Fe Up to Super-Earth Interior Conditions

Year: 2025

Type: article

Abstract: Equation of state (EoS) parameters of hexagonal close-packed iron (hcp-Fe), the dominant core component in large terrestrial planets, is crucial for studying interior structures of super-Earths. However, EoS parameters at interior conditions of super-Earths remain poorly constrained, and extrapolating from Earth’s core conditions introduces significant uncertainties at TPa pressures. Here, we compiled experimental static and dynamic compression data and theoretical data up to 1374 GPa and 12,000 K from the literature to refine the EoS of hcp-Fe. Using the third-order Birch–Murnaghan and Mie–Grüneisen–Debye equations, we obtained V0 (unit-cell volume) = 6.756 (10) cm3/mol, KT0 (isothermal bulk modulus) = 174.7 (17) GPa, KT0′ (pressure derivative of KT0) = 4.790 (14), θ0 (Debye temperature) = 1209 (73) K, γ0 (Grüneisen parameters) = 2.86 (10), and q (volume-independent constant) = 0.84 (5) at ambient conditions. These parameters were then incorporated into an interior model of CoRoT-7b and Kepler-10b, which includes four solid compositional layers (forsterite, MgSiO3 perovskite, post-perovskite, and hcp-Fe). The model yields the core mass fractions (CMF) of 0.1709 in CoRoT-7b and 0.2216 in Kepler-10b, suggesting a Mars-like interior structure. Extrapolation uncertainties (±10–20% in density) can change CMF by −12.6 to 21.2%, highlighting the necessity of precise EoS constraints at the super-Earth interior conditions.

Source: Crystals

DOI: 10.3390/cryst15030221

Authors: Yanyao Zhang, Shichang Zhang, Dongyang Kuang, Chao Xiong

Institutions: Stanford University, Hunan University of Technology and Business, Sun Yat-sen University

Language: English

Topic: High-pressure geophysics and materials

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,534

Funder: Sun Yat-sen University