Observation of body-centered cubic iron above 200 gigapascals

Year: 2026

Type: article

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.

Source: Physical review. B./Physical review. B

DOI: 10.1103/kxnf-6c5y

Institutions: European X-Ray Free-Electron Laser, Earth and Planets Laboratory, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Centre National de la Recherche Scientifique, Université de Lille, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement, Unité Matériaux et Transformations, Centrale Lille Institut, Deutsches Elektronen-Synchrotron DESY, Institut des Sciences de la Terre, Université Grenoble Alpes, Stony Brook University, Sorbonne Université, Muséum national d'Histoire naturelle, Institut de minéralogie, de physique des matériaux et de cosmochimie, Chimie de la Matière Condensée de Paris, Lawrence Livermore National Laboratory, Diamond Light Source, University of Oxford, University of Chicago, University of Saskatchewan, University of Freiburg

Language: English

Topic: High-pressure geophysics and materials

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: hybrid

Awards: G1088636562, G1092422733, G1356433355, G14554683, GOALS AND OBJECTIVES: THE OBJECTIVE OF THE PROPOSED WORK IS TO PROVIDE ADDITIONAL EXPERIMENTAL CONSTRAINTS FOR THE FURTHER DEVELOPMENT OF A COMPREHENSIVE BAROMETRY AND THERMOMETRY OF IMPACT STRUCTURES AND SHOCKED METEORITES. THE MINERALOGICAL RECORD PRESERVED IN IMPACT CRATERS AND SHOCKED METEORITES PROVIDE A UNIQUE WINDOW INTO SOLAR SYSTEM FORMATION AND PLANETARY EVOLUTION. THE IMPACT AND EJECTION PROCESSES CAUSE DRAMATIC CHANGES IN THE MICROSTRUCTURE CRYSTAL STRUCTURE AND POTENTIALLY THE ISOTOPE COMPOSITION OF THE MINERAL ASSEMBLAGE. HENCE THE COMMONLY USED SHOCK CLASSIFICATION MODELS ASSIGNS SHOCK LEVELS FROM UNSHOCKED (S1) TO VERY STRONGLY SHOCKED (S6) BASED ON MICROSTRUCTURE AND MINERAL PHASES. THESE CLASSIFICATION MODELS ARE MAINLY DERIVED FROM CHARACTERIZATION OF METEORITES AND ROCKS FROM KNOWN IMPACT SITES AND FURTHER CONSTRAINED BY EXPERIMENTAL DATA FROM STATIC AND DYNAMIC COMPRESSION EXPERIMENTS. HOWEVER THE EXPERIMENTAL CHARACTERISTICS IN STATIC AND DYNAMIC COMPRESSION EXPERIMENTS SUCH AS INVESTIGATED TIMESCALES AND PRESSURE-TEMPERATURE COUPLING ARE NOT A DIRECT REPLICATION OF THE NATURAL SHOCK CONDITIONS. THEREFORE THE RESULTS FROM STATIC AND DYNAMIC COMPRESSION EXPERIMENTS PROVIDE UPPER AND LOWER BOUNDARIES FOR THE BAROMETRY AND THERMOMETRY OF IMPACT STRUCTURES. FOR EXAMPLE THE EXISTENCE OF HIGH PRESSURE POLYMORPHS SUCH AS RINGWOODITE MAJORITE AND BRIDGMANITE IN SHOCKED METEORITES CANNOT BE EXPLAINED FOLLOWING THE ESTABLISHED SHOCK BAROMETER AND THERMOMETER SINCE HIGH SHOCK PRESSURE RESULTING IN HIGH BULK ROCK TEMPERATURES WOULD FAVOR A BACK TRANSFORMATION TO THE RESPECTIVE LOW PRESSURE POLYMORPHS., G1710736275, G1753116622, G2071550047, G2145270357, G249327869, G2717806384, G2908935449, Frontier Experiments in Dynamic Extreme Conditions: The Case for Light Elements, G3669113783, G3772249671, HBCU Excellence in Research: Research and Education Center for Investigation of Chemical Transformations in Host-Guest Systems at Extreme Conditions, Exploiting the European XFEL for a New Generation of High Energy Density and Materials Science, G39620777, G4301142815, G4576448283, Planetary Origins and Development (OxPOD), G4757599054, Facility Support: GeoSoilEnviroCARS: A National Resource for Earth, Planetary, Soil and Environmental Science Research at the APS, G5015276450, G5189429712, Planetary Interiors Constrained by Key Laboratory Experiments, G623270878, MINeralogical DIversity in (eXo)planets Interiors, G6441358257, G663679826, G6692798979, Deep Earth Mantle Phase Transition Maps: Studied by Time-Resolved Experiments, G687565771, G7245378827, G7415107377, TRansport in the InterioR of the Earth from Modelling and Experiments, Thermal conductivity of lower mantle minerals and outer core alloys studied by combined fast pulsed laser and optical spectroscopy techniques, G895790057, G991281326

OpenAlex ID: W4415328920