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Published March 2022 | Supplemental Material
Journal Article Open

Measurements of the Lamb-Mössbauer factor at simultaneous high-pressure-temperature conditions and estimates of the equilibrium isotopic fractionation of iron

Abstract

Isotopic fractionation has been linked to the lattice vibrations of materials through their phonon spectra. The Lamb-Mössbauer factor (f_(LM)) has the potential to provide information about the lattice vibrations in materials. We constrain the temperature evolution of the f_(LM) of γ- and ε-Fe at in situ high-P-T conditions between 1650 K and the melting point. We find that the vibrations of γ- and ε-Fe can be described using a quasiharmonic model with a pressure- and temperature-dependent Debye temperature computed from the measured f_(LM). From the Debye temperature, we derive the equilibrium isotopic fractionation β-factor of iron. Our results show that the quasiharmonic behavior of metallic iron would lower the value of lnβ_(Fe)^(57/54) by 0.1‰ at 1600–2800 K and 50 GPa when compared to the extrapolation of room temperature nuclear resonant inelastic X-ray scattering data. Our study suggests that anharmonicity may be more prevalent in Fe metal than in lower mantle minerals at 2800 K and 50 GPa, a relevant condition for the core formation, and the silicate mantle may be isotopically heavy in iron.

Additional Information

© 2022 by the Mineralogical Society of America. The authors thank Thomas S. Toellner for his help with the experiments. We also thank Lisa Mauger for kindly providing the published phonon DOS of α-Fe from her paper. The authors acknowledge Veniamin B. Polyakov, Aleksandr Chumakov, and Paolo Sossi for their thoughtful, thorough and constructive comments, which helped to improve our manuscript. We thank the National Science Foundation (EAR-CSEDI-1316362, EARCSEDI-2009935, and EAR-1727020) for support of this research. Use of the Advanced Photon Source is supported by the Department of Energy, Office of Science (DE-AC02-06CH11357). Sector 3 operations are supported in part by COMPRES under National Science Foundation Cooperative Agreement EAR-1661511. We thank GeoSoilEnviroCARS (NSF EAR-1634415 and DOE DE-FG02-94ER14466) for the help with sample preparation. D.Z. acknowledges the Argonne Graduate Research Program to support part of this research.

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Created:
August 22, 2023
Modified:
October 24, 2023