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Title: Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa

Multigrain X-ray diffraction (XRD) can be used to accurately calculate the unit cell parameters of individual mineral phases in a mineral assemblage contained in a diamond anvil cell (DAC). Coexisting post-perovskite (ppv) and H-phase were synthesized at 119 GPa and 2500 K from (Mg 0.85Fe 0.15)SiO 3 in a laser-heated DAC. The unit cell parameters of the ppv and coexisting H-phase were determined using multigrain XRD with a 5 μm spatial resolution, close to the size of the X-ray beam, to understand compositional variations across the center area (20–30 μm) in a laser-heated sample. The ppv phase was Fe-depleted and the unit cell volume of ppv decreased by only 0.16 % (corresponding to ~3 % variation of FeSiO 3) from the heating center to 10 μm off the center, while the sample pressure remained at 119 GPa in a Ne quasi-hydrostatic environment. The unit cell volume of the H-phase decreased by 0.54 % (~10 % variation of FeSiO 3 content) over the same 10 μm distance. Both phases were more Fe-enriched in the slightly hotter center. This observation suggests that thermal diffusion may not be the major driver for the compositional variations of ppv and H-phase in the center portionmore » of a laser-heated sample. Instead, these variations could be caused by a temperature effect on the partitioning between the ppv and H-phase over the small gradient.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China)
  2. Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab., High Pressure Collaborative Access Team (HPCAT)
  3. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China); Carnegie Inst. of Washington, Washington, DC (United States). Geophysical Lab.
Publication Date:
Grant/Contract Number:
NA0001974; AC02-06CH11357; FG02-94ER14466; FG02-99ER45775
Type:
Accepted Manuscript
Journal Name:
Progress in Earth and Planetary Science
Additional Journal Information:
Journal Volume: 3; Journal Issue: 1; Journal ID: ISSN 2197-4284
Publisher:
Springer Open
Research Org:
Carnegie Inst. of Washington, Washington, DC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Lower mantle; Multigrain XRD; Diamond anvil cell; Post-perovskite; H-phase; Unit cell; Synchrotron X-ray
OSTI Identifier:
1466599

Zhang, Li, Meng, Yue, and Mao, Ho-kwang. Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa. United States: N. p., Web. doi:10.1186/s40645-016-0091-8.
Zhang, Li, Meng, Yue, & Mao, Ho-kwang. Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa. United States. doi:10.1186/s40645-016-0091-8.
Zhang, Li, Meng, Yue, and Mao, Ho-kwang. 2016. "Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa". United States. doi:10.1186/s40645-016-0091-8. https://www.osti.gov/servlets/purl/1466599.
@article{osti_1466599,
title = {Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa},
author = {Zhang, Li and Meng, Yue and Mao, Ho-kwang},
abstractNote = {Multigrain X-ray diffraction (XRD) can be used to accurately calculate the unit cell parameters of individual mineral phases in a mineral assemblage contained in a diamond anvil cell (DAC). Coexisting post-perovskite (ppv) and H-phase were synthesized at 119 GPa and 2500 K from (Mg0.85Fe0.15)SiO3 in a laser-heated DAC. The unit cell parameters of the ppv and coexisting H-phase were determined using multigrain XRD with a 5 μm spatial resolution, close to the size of the X-ray beam, to understand compositional variations across the center area (20–30 μm) in a laser-heated sample. The ppv phase was Fe-depleted and the unit cell volume of ppv decreased by only 0.16 % (corresponding to ~3 % variation of FeSiO3) from the heating center to 10 μm off the center, while the sample pressure remained at 119 GPa in a Ne quasi-hydrostatic environment. The unit cell volume of the H-phase decreased by 0.54 % (~10 % variation of FeSiO3 content) over the same 10 μm distance. Both phases were more Fe-enriched in the slightly hotter center. This observation suggests that thermal diffusion may not be the major driver for the compositional variations of ppv and H-phase in the center portion of a laser-heated sample. Instead, these variations could be caused by a temperature effect on the partitioning between the ppv and H-phase over the small gradient.},
doi = {10.1186/s40645-016-0091-8},
journal = {Progress in Earth and Planetary Science},
number = 1,
volume = 3,
place = {United States},
year = {2016},
month = {5}
}