Observation of Body-Centered Cubic Iron above 200 Gigapascals
Abstract
The crystallographic structure of iron under extreme conditions is a key benchmark for cutting-edge experimental and numerical methods. Moreover, it plays a crucial role in understanding planetary cores, as it significantly influences the interpretation of observational data and, consequently, insights into their internal structure and dynamics. However, even the structure of pure solid iron under the Earth's core conditions remains uncertain, with the commonly expected hexagonal close-packed structure energetically competitive with various cubic lattices. In this study, iron was compressed in a diamond anvil cell to above 200 GPa, and dynamically probed near the melting point using MHz frequency X-ray pulses from the European X-ray Free Electron Laser. The emergence of an additional diffraction line at high temperatures suggests the formation of an entropically stabilized bcc structure. Rapid heating and cooling cycles captured intermediate phases, offering new insights into iron's phase transformation paths. The appearance of the bcc phase near melting at extreme pressures challenges current understanding of the iron phase diagram under Earth's core conditions.
Cite
@article{arxiv.2505.15397,
title = {Observation of Body-Centered Cubic Iron above 200 Gigapascals},
author = {Zuzana Konopkova and Eric Edmund and Orianna B Ball and Agnes Dewaele and Helene Ginestet and Rachel J Husband and Nicolas Jaisle and Cornelius Strohm and Madden S Anae and Daniele Antonangeli and Karen Appel and Marzena Baron and Silvia Boccato and Khachiwan Buakor and Julien Chantel and Hyunchae Cynn and Anand P Dwivedi and Lars Ehm and Konstantin Glazyrin and Heinz Graafsma and Egor Koemets and Torsten Laurus and Hauke Marquardt and Bernhard Massani and James D McHardy and Malcolm I McMahon and Vitali Prakapenka and Jolanta Sztuk-Dambietz and Minxue Tang and Tianqi Xie and Zena Younes and Ulf Zastrau and Alexander F Goncharov and Clemens Prescher and Ryan S McWilliams and Guillaume Morard and Sebastien Merkel},
journal= {arXiv preprint arXiv:2505.15397},
year = {2025}
}