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Published January 2021 | Supplemental Material + Published
Journal Article Open

Femtosecond X-Ray Diffraction of Laser-Shocked Forsterite (Mg₂SiO₄) to 122 GPa

Abstract

The response of forsterite, Mg₂SiO₄, under dynamic compression is of fundamental importance for understanding its phase transformations and high‐pressure behavior. Here, we have carried out an in situ X‐ray diffraction study of laser‐shocked polycrystalline and single‐crystal forsterite (a‐, b‐, and c‐orientations) from 19 to 122 GPa using the Matter in Extreme Conditions end‐station of the Linac Coherent Light Source. Under laser‐based shock loading, forsterite does not transform to the high‐pressure equilibrium assemblage of MgSiO₃ bridgmanite and MgO periclase, as has been suggested previously. Instead, we observe forsterite and forsterite III, a metastable polymorph of Mg₂SiO₄, coexisting in a mixed‐phase region from 33 to 75 GPa for both polycrystalline and single‐crystal samples. Densities inferred from X‐ray diffraction data are consistent with earlier gas‐gun shock data. At higher stress, the response is sample‐dependent. Polycrystalline samples undergo amorphization above 79 GPa. For [010]‐ and [001]‐oriented crystals, a mixture of crystalline and amorphous material is observed to 108 GPa, whereas the [100]‐oriented forsterite adopts an unknown phase at 122 GPa. The first two sharp diffraction peaks of amorphous Mg₂SiO₄ show a similar trend with compression as those observed for MgSiO₃ in both recent static‐ and laser‐driven shock experiments. Upon release to ambient pressure, all samples retain or revert to forsterite with evidence for amorphous material also present in some cases. This study demonstrates the utility of femtosecond free‐electron laser X‐ray sources for probing the temporal evolution of high‐pressure silicate structures through the nanosecond‐scale events of shock compression and release.

Additional Information

© 2020. American Geophysical Union. Issue Online: 15 January 2021; Version of Record online: 15 January 2021; Accepted manuscript online: 04 December 2020; Manuscript accepted: 02 December 2020; Manuscript revised: 18 November 2020; Manuscript received: 07 June 2020. The authors are grateful to Carol Davis from the target fabrication team at Lawrence Livermore National Laboratory (LLNL) and the staff at Matter in Extreme Conditions end‐station for experimental assistance. A. M. Dillman and J. L. Mosenfelder synthesized the sintered polycrystalline samples. Gregory J. Finkelstein provided helpful comments on the manuscript. This research was supported by the U.S. Department of Energy (DE‐SC0018925) and the National Science Foundation (NSF) (EAR‐1644614). AEG acknowledges support from LANL Reines LDRD and the NSF Geophysics Program EAR‐1446969. PDA acknowledges support from NSF Geophysics Program award EAR‐1725349. M. O. Schoelmerich and K. Appel acknowledge support from the German Research Foundation DFG (AP 262/2‐1 and FOR2440). This work was also performed under the auspices of the U.S Department of Energy by LLNL under contract No. DE‐AC52‐07NA27344. The use of the Linac Coherent Light Source, SLAC National Accelerator Laboratory, is supported by the Department of Energy, Office of Science, Office of Fusion Energy Sciences under Contract no. DE‐AC02‐76SF00515. Data Availability Statement: Additional experimental parameters and details of data extraction are available in the supporting information. Data from this work are archived in the Department of Geosciences community of Princeton University's DataSpace: http://arks.princeton.edu/ark:/88435/dsp01rj4307478.

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Published - 2020JB020337.pdf

Supplemental Material - 2020jb020337-sup-0001-figure_si-s01.docx

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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023