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Femtosecond X‐Ray Diffraction of Laser‐Shocked Forsterite (Mg 2 SiO 4 ) to 122 GPa
Author(s) -
Kim Donghoon,
Tracy Sally J.,
Smith Raymond F.,
Gleason Arianna E.,
Bolme Cindy A.,
Prakapenka Vitali B.,
Appel Karen,
Speziale Sergio,
Wicks June K.,
Berryman Eleanor J.,
Han Sirus K.,
Schoelmerich Markus O.,
Lee Hae Ja,
Nagler Bob,
Cunningham Eric F.,
Akin Minta C.,
Asimow Paul D.,
Eggert Jon H.,
Duffy Thomas S.
Publication year - 2021
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2020jb020337
Subject(s) - forsterite , crystallite , materials science , amorphous solid , laser , diffraction , phase (matter) , femtosecond , silicate perovskite , crystal (programming language) , periclase , analytical chemistry (journal) , electron diffraction , mineralogy , crystallography , optics , perovskite (structure) , chemistry , metallurgy , physics , programming language , magnesium , organic chemistry , chromatography , computer science
The response of forsterite, Mg 2 SiO 4 , 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 MgSiO 3 bridgmanite and MgO periclase, as has been suggested previously. Instead, we observe forsterite and forsterite III, a metastable polymorph of Mg 2 SiO 4 , 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 Mg 2 SiO 4 show a similar trend with compression as those observed for MgSiO 3 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.