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Observation of body-centered cubic iron above 200 gigapascals

Zuzana Konôpková1,*,†, Eric Edmund2,*,‡, Orianna B. Ball3, Agnès Dewaele4,5, Hélène Ginestet6, Rachel J. Husband1,7, Nicolas Jaisle8, Cornelius Strohm7, Madden S. Anae9 et al.

Daniele Antonangeli10, Karen Appel1, Marzena Baron11, Silvia Boccato10, Khachiwan Buakor1, Julien Chantel6, Hyunchae Cynn12, Anand P. Dwivedi1, Lars Ehm9, Konstantin Glazyrin7, Heinz Graafsma7, Egor Koemets13,14, Torsten Laurus7, Hauke Marquardt13, Bernhard Massani3, James D. McHardy3, Malcolm I. McMahon3, Vitali Prakapenka15, Jolanta Sztuk-Dambietz1, Minxue Tang7, Tianqi Xie16,9, Zena Younes3, Ulf Zastrau1, Alexander F. Goncharov2, Clemens Prescher17, Ryan S. McWilliams3, Guillaume Morard10,8, and Sébastien Merkel6

  • *These authors contributed equally to this work.
  • †Contact author: zuzana.konopkova@xfel.eu
  • ‡Present address: Universität Münster, Münster, Germany.
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Phys. Rev. B 114, 094103 – Published 10 August, 2026

DOI: https://doi.org/10.1103/kxnf-6c5y

Abstract

The crystallographic structure of iron under extreme conditions is a key benchmark for state-of-the-art experimental and computational methods. Moreover, it plays a crucial role in our understanding of planetary cores, as it strongly influences the interpretation of observational data and, consequently, our knowledge of their internal structure and dynamics. However, even the crystal structure of pure solid iron under Earth's core conditions remains uncertain, with the commonly expected hexagonal close-packed phase being energetically competitive with several cubic structures. In this study, iron was compressed in a diamond anvil cell to pressures exceeding 200 GPa and dynamically probed near its melting point using MHz-frequency x-ray pulses from the European X-ray Free-Electron Laser. In the pressure range between 120 and 160 GPa, the high temporal resolution of the structural snapshots at elevated temperatures revealed the face-centered cubic phase, extending its observed stability to higher pressures than previously reported. Brief appearances of intermediate or disordered phases, including body-centered cubic (bcc) and stacking-faulted structures, were also observed. Above 230 GPa, new diffraction reflections emerged at high temperatures and are interpreted as evidence for the nucleation of a previously unreported phase, which subsequently evolved into a powderlike diffraction pattern characteristic of the bcc structure. The unprecedented time resolution of the structural data acquired during rapid heating and cooling cycles provides insights into the kinetics and mechanisms of phase transformations in iron at these extreme pressures.

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Phys. Rev. B 114, 094103– Published 10 August, 2026
  • Received 21 February 2025
  • Revised 13 July 2026
  • Accepted 15 July 2026
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