Observation of body-centered cubic iron above 200 gigapascals

Under Earth’s core-like pressures, iron’s expected hexagonal structure energetically competes with other cubic forms. This study probes the state of iron near its melting temperature using series of femtoseconds X-ray pulses of the European XFEL. Between 120–160 GPa, a stable hexagonal phase is confirmed, with brief transient disordered or cubic phases appearing. Above 200 GPa, a new diffraction peak emerges, characteristic of a body-centered cubic (bcc) structure. Following this uncommon kinetic and pressure-temperature path, the bcc structure is shown to be stable, providing exciting insights into the kinetics, stability, and transformation mechanisms of iron under these conditions.

The paper is led by our colleague Zuzana Konôpková at the European XFEL and Eric Edmund, formerly at the Earth & Planets Laboratory, Carnegie Science, and is a result of the EuXFEL #3063 community experiment on iron and iron alloys under planetary cores conditions which was led by S. Merkel. These experiments produced terabytes of data which we are still crunching on today.

Within the HotCore's project, and for the whole high pressure and deep Earth communities, these results came as a big surprise. The stable form of iron at Earth's core conditions has been assumed to be the hexagonal structure for decades, but it was known that other cubic structures could energetically compete and become stable as well. Here, we show that using a nonconventional crystallization path, by dropping temperature by several thousands of kelvins over 220 nanoseconds at pressures over 200 GPa, we can indeed stabilize a body-centered cubic (bcc) structure over the timescale of the experiment.

Whether this form of iron actually exists within the Earth's core remains an open question, but our experiments show that, in fact, one can form a cubic phase of iron under Earth's core pressures and temperatures.

The paper was published in Physical Review B on August 10, 2026: Z. Konôpková, E. Edmund, O. B. Ball, A. Dewaele, H. Ginestet, R. J. Husband, N. Jaisle, C. Strohm, M. S. Anae, D. Antonangeli, K. Appel, M. Baron, S. Boccato, K. Buakor, J. Chantel, H. Cynn, A. P. Dwivedi, L. Ehm, K. Glazyrin, H. Graafsma, E. Koemets, T. Laurus, H. Marquardt, B. Massani, J. D. McHardy, M. I. McMahon, V. Prakapenka, J. Sztuk-Dambietz, M. Tang, T. Xie, Z. Younes, U. Zastrau, A. F. Goncharov, C. Prescher, R. S. McWilliams, G. Morard & S. Merkel. Observation of body-centered cubic iron above 200 gigapascals (2026) Physical Review B  114 [doi: 10.1103/kxnf-6c5y]

It was also highlighted as the Editor's suggestion for the corresponding issue.